Best posts made by Korina

Update: 21st of May, 8:00 a.m. UTC

After hammering India and Bangladesh, Amphan is forecasted to move north-northeastward and weaken into a depression later today. The maximum sustainable winds, which may be carried by the storm, are 50 km/h (27 KT).

Thunderstorms with gusty winds are likely to occur over Bihar and isolated places such as Assam, Arunachal Pradesh and Meghalaya.

Due to the correct timing of rescue teams deployment, there is a minimum human loss.
The worst damages has been concentrated in the West Bangal districts and Sunderbans, which suffered immense destruction.

Update: 20th of May, 4:00 p.m. UTC

The super cyclone Amphan hits India and Bangladesh with its landfall between Indian town of Digha and Hatiya Islands in Bangladesh. Storm is dumping heavy rain and damaging winds on Kolkata leaving a trails of destruction. Reported damages are destroyed houses, power cuts and downed trees.

Cyclone is now moving at 31km/h (17 KT) near 22.2N 88.3E, roughly 25 NM from Kolkata with maximum sustainable winds 138 km/h (75 KT) and gusts 166 km/h (90 KT).

Amphan will move north-northeasterly passing trough the Sunderbans and gradually weaken.

Update: 20th of May, 8:00 a.m. UTC

TC Amphan was moving at 25 km/h (14 KT) near 20.5N 87.9E approximately 129 NM South-Southwest of Kolkata in the last 6 hours. Maximum sustained winds were 157 km/h (85 KT) and gusts 194 km/h (105 KT), which makes it a Category 2 Atlantic hurricane and the strongest storm ever recorded in the Bay of Bengal.

Anticipated landfall still remains for Wednesday evening hours local time (5:30 pm Wednesday IST) near or just east of Hooghly River south of Kolkata.

Impacts

Cyclone could bring very strong storm surges up to 5 meters (16.4 feet), causing roadblocks, power link outages and destruction of houses and crops.

Evacuation of people continues, but a pandemic situation puts a great stress on the whole operation as it became difficult to maintain social distancing.

Update: 19th of May, 02:00 p.m. UTC

Super cyclone Amphan has been already marked as extremely intense in the region and the second strongest storm since 1999. Cyclone is due to make the landfall into West Bengal, Digha and Hatiya Island in Bangladesh during Wednesday morning.

In the last 6 hours, cyclone was moving 16 km/h (09 knots), located at 17.0N 86.9E, 377 NM South-Southwest of Kolkata, India with maximum sustainable winds 203 km/h (110 KT), gusts 250 km/h (135 KT).

Impacts

Storm is expected to weaken before the landfall, but the results could be still devastating with heavy rainfall and tidal waves causing flooding and strong winds resulting in significant physical damage.

Update: 19th of May, 00:00 a.m. UTC

Amphan has strengthened to a Category 5 hurricane, its position is approximately 480 NM south-southwest of Kolkata, India - 15.2N 86.6E, the current movement has been at 14 km/h (08 knots) in the past 6 hours.

The maximum sustained winds are 240.76 km/h (130 KT) and gusts 296.32 km/h (160 KT). The landing will be likely between Kolkata, India, and Chittagong, Bangladesh on Wednesday afternoon or evening. Cyclone is expected to be a hurricane Category 3, when it makes the landfall.

There are already signs of eyewall replacements, which could halt the Amphan's further intensifying. However even if the winds weaken, the real dangers is going to be a potential catastrophic storm surge up to 4–6 meters (13–20 feet).

Update: 18th of May, 12:00 a.m. UTC

TC Amphan is moving near 13.6N 86.4E with maximum sustainable winds 259 km/h (140 KT) and gusts 314 km/h (170 KT).

The cyclone is expected to hit Odisha states and West Bengal on Wednesday noon local time as a super cyclonic storm. Amphan will gain strength in the next 12 hours, but could weaken as it reaches the coasts.

Odisha state is already evacuating citizens to a cyclone shelters, more than a milion people is planned to be evacuated from coastal areas.

Update: 17th of May, 4:00 p.m. UTC

Tropical cyclone Amphan is currently strengthening in the Bay of Bengal near position 12.0N 86.4E with maximum sustainable winds 138 km/h (075 KT) and gusts 166 km/h (090 KT).

At the moment the cyclone is a category 1 on a hurricane scale and could likely become a hurricane category 3, when it reaches coasts in the northeast. The landfall is predicted to occur from Tuesday night through Wednesday.

The movement for next 12 hours is forecasted to be near 13.1N 86.5E and winds 157 km/h (085 KT), gusts 194 km/h (105 KT).

Impacts

Amphan will bring a strong winds and heavy rainfall, causing dangerous flooding with a possibility of a storm surge for vulnerable areas, especially for Bangladesh.

https://www.windy.com/upload/5ec16efe6d85e3001d6ecd01?satellite,20.108,85.761,6,internal

Reading the latest news, everybody has to be concerned about the Coronavirus and its impact on daily life of billions of people. The Coronavirus (virus is officially labeled as SARS-CoV-2 and its disease as COVID-19) is spreading quickly around the world, causing unprecedented lockdowns of huge regions and cities, havoc on markets and overload of health facilities in affected areas.

Some countries seem to have already contained the major spread of virus (China, South Korea), some are currently experiencing the initial extreme increase of patients with severe cases (Italy, Iran), with the rest of the world expecting it in upcoming weeks and trying to prepare for it.

Question is, will the rate of spread slow down or even disappear at all? It definitely will.

Check this nice video demonstrating the principle of exponential growth and epidemics

It’s essential to understand that even a very small decrease in “probability of exposure becoming an infection” (referred as p in the video) can reduce the growth of the spread significantly or even stop it completely.

But why do we discuss it at Windy.com, we normally talk just weather, right?

The reason is the outside temperature. Spread of typical flu highly correlates with weather, having its season peak in cold months, declining during spring with almost no cases during the warmest part of the year. Recent studies show that high temperatures and especially high humidity slows the influenza spread. More moisture in warmer air behaves as a barrier for airborne viruses so droplets of cough or sneeze cannot travel as far as they would in colder, dry air.
Of course, more factors can play a role in this flu seasonality (longer sunlight exposure, less clustering of people indoors), but temperature is considered as the major one.

There is a whole family of coronaviruses, some of them already known to humans, causing mild colds and behaving similar to the flu - in warmer climate, they tend to decline. That is the reason why many people believe that same will happen with COVID-19. As stated above, even the slight decrease in person to person transfer rate of the virus has a huge impact on overall number of cases. Will a higher temperature and humidity help us in this way? There are many opinions on that subject, but most experts agree, that it’s too early to judge and only hard data from summer season and their detailed analysis will tell us the truth.

But until then, we have no other option than to make assumptions based on data we have now.

Posts discussing weather patterns (temperature/humidity):

Also check out:
Coronavirus outbreakt

The perspective

As mentioned, the COVID-19 is not all that unknown to us, we had coronavirus strain SARS back in 2003. SARS had its peak in winter months and faded away during May. Typically influenza season falls sometimes between the beginning of fall and the end of spring. So the SARS did not really exceed the usual influenza season trend. But can we expect COVID-19 to follow this path as well?

The current spreading rate tells us a fact, that the COVID-19 has more incidences in places with dryer and colder environment than in more humid and warm locations. For instance let´s take a look at Japan, we would expect the virus to be spreading mainly in big cities like Tokyo, due to a number of foreign visitors and population. But this is not the case, COVID-19 is actually spreading in Hokkaido, despite it has a much lower frequency of travellers. However the weather conditions there are favorable, dry and less humid environment. The same goes for Italy and its epicenter Milan. North of the country is significantly more affected than the south.

On the other hand, it would not be wise to expect the novel coronavirus to behave as the ones before.
It is necessary to say, that SARS 2003 did not go away just because weather got warmer. It was followed by national interventions to isolate cases and everyone, who had the possibility to be infected.

We have already said that the environment plays a key role in influenza activity and dry/cold weather with low humidity favors the transmission. But influenza epidemics often appears in a tropical and subtropical regions during rainy seasons with obviously high humidity values. In other words, there are two types of influenza environments. In cold-dry environment, where humidity/temperature goes below 11–12 g/kg and 18–21°C, influenza peaks during cold months. In humid-rainy case, if humidity/temperature does not go under those values, influenza peaks during rainy season.

Immunity is another factor, which is worth a consideration. Our immunity is significantly worse in winter than in summer and we also lack vitamin D, because of less ultraviolet light exposure in cold months. Vitamin D benefits our immune system and helps us to be durable against numerous diseases, even so this factor can be observed as not so important in relation to influenza activity.

But then again, new viruses are likely to persist longer than a common ones, which have been in the population for years or decades.

Available data

We at Windy.com are no experts in the area of viruses, but we have access to the best weather data available.

We have assembled temperature records for each country (taken from the area of major spread of the virus within the country or the capital of that country) and pictured them along with recent Coronavirus spread data (daily amount of new cases, sourced from Coronavirus COVID-19 Global Cases by Johns Hopkins CSSE) to see if there could be any correlation.

Based on the charts above, we can see a slight correlation in relation with a higher temperature and virus decrease, and opposite a lower temperature and faster spread of COVID-19.

Of course, there are many drawbacks in this approach:

• data coming from different countries aren’t easily comparable (some countries test much more than the others, some have much highly populated areas, also quality of data coming from some countries is more than questionable)

• the virus has quite a long incubation period, therefore “new” cases are being reported several days after the people were actually infected (but at least average temperature at given location can help to mitigate this effect)

• there are still not that many daily observations, the data window is quite too small

• correlation does not imply causation” - even if there seems to be a visual dependency between the temperature and the increase/decrease rate of new cases, it is absolutely no proof that there is a correlation between those two

As always there are many opinions and very little data to predict anything for sure. So the truth will be somewhere in the middle. It should be essential to avoid any catastrophic predictions as well as not to underestimate it.

The latest data for China shows a retreat of Coronavirus cases and high amount of recovered patients in a comparison to the total amount. Other countries will hopefully have the same progress.

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Not happy with the findings? Don’t despair. If the weather won’t help us, there are still many ways, how each of us can help - avoid crowded places, work remotely if possible, stay fit, wash your hands, do not touch your face.
Avoid face to face social contacts for a while - read a couple of books or go online! There is still a lot to explore, also at Windy.com.

Update: 4th June 00:00 UTC

TC Nisarga is now moving northeastwards towards Nashik and continues to weaken, the current sustainable winds are 75km/h (40 KT). Movement speed was 27 km/h (14 KT) in the last 6 hours.

Dhule and Nandurbar districts may experience heavy rainfall and gusty winds.

Track the latest severe weather predictions with the most accurate data, subscribe to Windy Premium and get 1 hour forecast with detailed informations.

Update: 3rd June 3:00 p.m. UTC

Tropical cyclone Nisarga, the equivalent of a Category 1 hurricane, battered western India with torrential rainfall and strong winds. It is also the first cyclone to strike the city of Mumbai in history.

The landfall itself did not cause major damages, despite the winds speeds more than 100km/h (53 KT) as it reached the land.

Moving further inland, cyclone lost its strength quickly and was downgraded to a deep depression. However the next few hours are still crucial.

Cyclone is now moving at 25 km/h (14 KT) with position 19.6N 74.2E. east of Mumbai, maximum sustainable winds are 60 km/h, gusts 90km/h (48 KT). Expected movement in the next 12 hours is 21.0N 75.8E.

Update: 3rd June 9:00 a.m. UTC

Nisarga has made a landfall around noon local time near Maharastra’s Raigad district with stronger maximum sustainable winds than expected 140 km/h (75 KT) and gusts 166 km/h (90 KT).

However the landfall is far from gone, it will take 3 hours to complete, the current position is 18.3N 73.3E, cyclone is located approximately 65 NM south of Mumbai.

The cyclone will move gradually over the land, the next expected direction is 19.5N 74.5E towards Panvel, Maharastra. Winds speeds should weaken to 92 km/h (50 KT), gusts 120 km/h (65 KT).

Update: 3rd June 5:00 a.m. UTC

Cyclone Nisarga has been moving at 13 km/h (7 KT) in the past 6 hours and its position is 17.2N 72.1E, 130km south-southwest of Alibagh, town in Maharashtra’s Raigad district.

The storm has intensified to maximum sustainable winds 110 km/h (59 KT) and gusts 120 km/h (64 KT).

Predicted landfall is today between 12pm and 3pm IST just the south of Alibagh. Heavy rainfall is expected with a storm surge of about 1-2 metres height.

This will affect low laying areas of Ratnagiri district mainly and Mumbai, which is on the path of the cyclone.

Update: 2nd June 9:00 a.m. UTC

A deep depression has intensified into a cyclonic storm in the Arabian Sea and is predicted to become a severe cyclonic storm named Nisarga in the next several hours. Storm has been moving at 11 km/h (5 KT) northwards in the past 6 hours.

The current maximum sustainable winds are 70 km/h (37 KT) and gusts 90 km/h (48 KT) with a position LAT 16.0/LON 71.5.

The strom could possibly bring a devastating winds of 110 km/h (59 KT) and gusting to 120 km/h (64 KT).

The expected landfall is either on Tuesday night or early Wednesday morning 3rd of June over Mumbai, north Maharashtra and Gujarat coasts.

https://www.windy.com/upload/5ed7547c18b9f0001d7b3c59?satellite,15.739,72.993,7,internal

We are proud to strengthen our partnership with The Copernicus Atmosphere Monitoring Service (CAMS) with 3 new CAMS layers being implemented on Windy.com. The official press release from Copernicus here.

Our ongoing partnership since 2019 has already brought visualization of several CAMS layers and empowering general public to observe climate changes at a global scale.

From now on, users can access CAMS data via three new layers: fire intensity, surface ozone and total column sulphur dioxide (SO2). The overal objective is to rise awareness of air pollution and provide air quality data in easy and understandable way.

“We are delighted to be working with Windy to integrate CAMS data, so that its many users can access our global and European-scale forecasts,” says Vincent-Henri Peuch, Director of CAMS.

“If air quality forecasts were as common as weather forecasts it would help inform the public and make people more aware about the need to combat air pollution. The way that Windy visualises CAMS data helps people to understand that air pollution is not simply a local problem, but can be transported hundreds or thousands of kilometres by winds. Using Windy, users can easily follow where air pollution is transported and where it accumulates.”

Surface ozone

Ozone is formed in the lower atmosphere through chemical reactions triggered by sunlight involving nitrogen oxides and volatile organic compounds.

Ozone is generally highest in spring and summer, downwind of areas with high levels of emissions. It is a toxic gas that causes cardiopulmonary and respiratory problems, and can affect crop yields, so being aware of local levels can be vital.

Total column Sulphur dioxide (SO2)

Sulphur dioxide is emitted from several sources, including volcanic eruptions and combustion of unrefined fossil fuels. This layer will show the amount of sulphur dioxide from the ground to the top of the atmosphere.

Fire intensity

This layer uses coloured pixels to indicate active fires. Thermal radiation from actively burning vegetation (including wildfires and agricultural open burning) is related to the rate at which fuel is being consumed and smoke produced, and so are also linked to emissions of trace gases and small airborne particles.

And it truly was.. Windy team once again went on an adventure, and this time we decided to conquer Norway and its snowy hills covered with picturesque cottages.

Our journey started on Prague’s airport, where we had a flight to Oslo and from there we took a long ride by car (5,5 hours) until we arrived in Ustaoset, Buskerud, where we stayed for a week on our colleague’s cottage. (Many thanks again to Honza for the invitation and the hospitality!).

There was really no shortage of snow. Ustaoset is 990m above the sea level and is the finish spot for the cross country ski event Skarverennet. So the scenery was great and view from cottage’s living room, even better.

Due to coming storm Dennis the weather was not ideal especially in the beginning of our week. So the first day we spent working and making plans for the upcoming days.

When the weather got better, there was a plenty of options what we could do!

Kiting

Probably the most tempting activity we all wanted to try was snowkiting. 
Since most of us are complete beginners, we had our instructors nearby to teach us the basic techniques to operate the kite and help us. 

Kiting is certainly not one of the easiest sports you can do, in the beginning, you spend quite a bit of time untangling your kite, because it tends to get out of control a lot and you have to put it in the air over and over again.
It frankly requires a bit of patience, but once you get into it, you will love it. 

It was a great feeling to chase winds on a snowy plains either on skies or snowboard.

A little different camping

Since we saw a chance to get the true nordic night experience firsthand, we took the challenge and a few of us decided to spend a night outside. 

We did have all the necessary equipment and experienced instructor to guide us through. So the fun could begin!

We had to start building two tents early in the afternoon to get things done in time. 
KP for aurora borealis was 4 at that time, so there was a little chance, but we still secretly hoped to catch it. 
A few hours later, the two tents were standing, tops of mountains started to get a pink tint and we were about to call it a day, cooked dinner and went to a bed early.

Nevertheless, since we know how to command weather, we did see aurora borealis in the end. 
In the morning, still in a shadow of the past night, green as an emerald, just as we all pictured it. :)

Skiing and the surprise

Norway has quite a few skiing resorts and the one we went to was Geilo. It happens to be the 5th best resort in Norway, located just a few kilometres from Ustaoset. The first impression was half empty slopes with a fresh powder snow, so actually really nice.

After we enjoyed a full day of sunny weather in the mountains, we joined an evening surprise, which was a night sledding and a hot bath outside for the more venturesome among us.

Here is a little sneak peek on how we pulled it off in the end:

Update: 28th of May 02:00 p.m. UTC

SpaceX launch of NASA Astronauts is postponed over the weather

Thunderstorms and light rain caused by Tropical Storm Bertha were the reason why mission Commercial Crew Demo-2 was aborted only 17 minutes before liftoff.

The Next attempt is scheduled for Saturday, 30 May at 7.22 PM UTC (3.22 PM EDT).

Although chances for success look similar, stormy weather with cloud cover is predicted, upper winds, which can drive thunderstorms to the coast, might be better. On the day of supposed launch, upper winds were moderate (13 kt/24 km/h), on Saturday will be light (4kt, 8 km/h).

In case the launch will be postponed again, the backup launch window for Falcon 9 is available 31 May at 7 PM UTC (3 PM EDT), with the same probability for success.

Update: 27th of May 01:00 p.m. UTC

The SpaceX first-ever crewed spaceflight is scheduled to take off from Cape Canaveral in Florida later today as a mission Commercial Crew Demo-2.

The launch is currently set to 08:30 p.m. (4:33 PM EDT) from Kennedy Space Center, however the weather conditions are not looking very favorable. There is currently a 50% chance that clouds and stormy weather will delay the proceedings due to violating the safety guidelines.

The Crew Dragon capsule will initially spend 19 hours orbiting the Earth till reaching the International Space Station on Thursday.

If the launch ends up to be postponed, another opportunity to send the capsule into the orbit will be on Saturday 30th May.

https://www.windy.com/upload/5ece9129f8e856001d015140?radar,28.229,-81.088,9,internal

Update: 14th of May, 10:00 p.m.

VongFong (Ambo) is moving westward across Samar Island with position 12.5N 123.6E and maximum sustained winds 74 km/h (065 KT) and gusts 92 km/h (080 KT). Typhoon has slightly weakened, however is still striking the island with extreme rainfall and typhoon-force winds.

Typhoon should continue loosing its strength further with a position at 13.5N 122.3E in the next 12 hours.

An estimated number of 200 000 people needs to be evacuated from their homes to avoid life-threatening flooding and landslides, but local authorities are already facing problems with finding shelters along with pandemic situation.

Update: 14th of May
Tropical typhoon VongFong with the current position near 12.2N 125.3E and maximum sustainable winds 185 km/h (100 KT) and gusts 231 km/h (125 KT) has arrived to Philippines.

The upcoming movement is near 12.8N 123.7E with winds 166 km/h (090 KT) and gusts 203 km/h (110 KT) and going deeper into Bicol regions and Visayas in the next 24 hours. The predicted scenario is VongFong striking Luzon during the Friday night, the largest island of the country, with heavy rains.

The situation is even more difficult since the country is under COVID 19 lockdown, so potential emergency efforts could be complicated by a strict social distancing of the evacuated citizens.

Update: 13th of May
The pacific typhoon season of 2020 has officially began, during the past few days a new tropical typhoon has developed in the Philippine Sea and was given an international name Vongfong, locally known as Ambo. The initial tropical depression was indicated on Sunday and progressed into Tropical Cyclone Formation Alert later on.

The former tropical storm is likely to reach Philippines ports on Thursday 14th of May and will most likely affect the Catanduanes Island with heavy wind and rainfall.

Vongfong is currently moving near 12.0N 128.5E with maximum sustainable winds 129 km/h (070 KT) and gusts 157 km/h (085 KT) with possibility of strenghtening as it gets closer to the northern ports.

Warning for heavy rainfall, landslides and flooding has been issued for the affected areas. Wind threat can also cause corrupting electricity, knocking down trees and roadblocks.

https://www.windy.com/upload/5ebc2b1f6d85e3001d6ecce9?satellite,16.220,123.871,5,internal

Update: 7:00 a.m. UTC 9th April

TC Harold is on its path to completely weaken and getting torn apart by a jet stream over the South Pacific open waters.
After his rampage track through the pacific nations Vanuatu and Fiji, Harold intensified to Category 5 hurricane and passed Tonga on Thursday 9th of April.

The current movement in the last 6 hours is 23.8S 172.1W with approximate position 545 NM Southeast of Suva, Fiji and wind speed 102 kts (188km/h) to 127 kts (235km/h). Cyclone is moving away from any land areas.

Update: At 9:00 p.m. UTC 8th April, Harold was moving at 22.5S 174.3W located approximately 408 NM Southeast of Suva, Fiji.

Cyclone slammed Tonga with gusts 150km/h, which were recorded near the Nuku'alofa, the Tongan Capital. However the center of Harold happened to pass about 100 miles south of Tongatapu and Eua islands and saving them from the most severe conditions.

Harold should continue to weaken in the next days over the South Pacific waters.

Update: At 5:00 p.m. UTC on April 8th

STC Harold category 4 hurricane is aiming towards Tongatapu and 'Eua tonight. High swells up to 20 ft (6 m) and tides with height of 1.87mm. The most severe conditions are expected to occur overnight and in the morning.

The current position is near 21.1S 176.9W. Cyclone is predicted to move 90km south-west of Nuku'alofa and 100km west south-west of 'Ohunua 'Eua Thursday morning.

Update: At 8:00 Zulu (8:00 a.m. UTC) on April 8th

Harold (category 5 hurricane) slams into the largest island of Fiji, Viti Levu and the capital city Suva, which has suffered with heavy flooding and buildings being demolished or damaged.

Tropical cyclone is moving near 19.4S 178.7E with maximum sustained winds 120 kt (222.24 km/h) gusts 145 kt (268.54 km/h).

Cyclone is expected to be moving to Tonga in the upcoming 48 hours, therefore a warning has been issued for extreme high tides on Thursday and Friday.

Update: At 10:00 a.m. EDT (15:00 UTC) on April 7th
Harold was issued with category 3 hurricane with maximum sustained winds 110 kt (203 km/h).
The cyclone centre was located 17.4S 174.0E and moving east-southeast to Fiji.

In the next 24hrs the maximum sustained winds should remain the same 110 kt (203 km/h) and gusts 135 kt (250 km/h).

The landfall of Harold is predicted on 8th April at 8:00 p.m. EDT (00:00 UTC) and move to the southeast near Tonga.*

Update: At 8:48 p.m. VUT Tuesday 7th April (9:48 a.m. UTC)

Tropical cyclone Harold [927hPa] is moving 17.1S 172.6E. This is about 430km east-northeast of Erromango and 465km east of Efate, which is part of Shefa Province in Vanuatu.
The current estimated maximum sustained winds are 110 kt (203 km/h) and gusts 135 kt (250 km/h).
Further predicted movement in the next 12 hrs is 18.5 South 175.9 East. Check out the latest Advisory at metoc.navy.mil*

Update to 6.4.2020 afternoon CET (evening in Vanuatu)

Tropical cyclone Harold arrived to Vanuatu with flooding surge, hurricane-force winds and heavy rainfall. Morning local time, the cyclone Harold reached Espiritu Santo, the largest island of Vanuatu with population of 40 000 people. And later moved towards the Pentecost Island.

As the cyclone is expected to move through the islands of Vanuatu, the warning has been issued. Heavy swells and high sea wind could be anticipated for coastal and open waters of Vanuatu. People are strongly adviced to avoid affected areas and not to go out on sea.

On Wednesday 8th of April, the cyclone Harold is expected to pass near Viti Levu, the Fiji's most populated island or just its southern parts.

The heavily affected area is Sanma province, the reported damages have been destroyed or lost buildings.

Date: 5.4.2020 (evening CET)

A tropical cyclone in the South Pacific Ocean named Harold is expected to hit Vanuatu in the upcoming hours. As of Sunday evening CET, the cyclone is now moving near the northern parts of Republic of Vanuatu is likely to intensify as it approaches the islands.

Heavy rain, strong damaging winds with surge flooding are expected. The current maximum sustained winds are expected to be 190km/h and could raise to 220km/h once it gets closer.

Harold can also target near or south of Fiji later this week, but the details are still uncertain.

The cyclone has formed last Wednesday in the area of Solomon Islands and Papua New Guinea.

Residents of Sanma, Penama and Malampa provinces should take proper actions to prepare themselves for heavy rainfall and hurricane-force winds.

We are thrilled to deliver our users tens of thousands of live webcams with new ones being added every day, and let them explore places as well as be informed about weather conditions anywhere and anytime through an eye of countless weather cams.

Windy Webcams is vividly growing platform of webcam owners, who make their webcams available to millions of users around the world, therefore we would like to encourage you to join our community!

Add your webcam on Windy.com and:

• have a quick access to your webcam from Windy along with beautiful weather animation
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How to add your webcam

The whole process is very easy and intuitive. The primary conditions are that your webcam must be up-to-date, weather oriented (indoor webcams are not suitable) and be publicly available on your site in order to be able to submit your webcam.

Detailed registration process is described in this article with registration form here.

Amid the COVID-19 measurements, Copernicus monitors a 10% per week reduction in NO2 surface concentrations since mid-February.

While the question of improved air quality is a secondary concern with the world facing the COVID-19 crisis, satellite observations detected abrupt changes in activity levels in Northern Italy, where dense surface observation of the pollutant nitrogen dioxide (NO2) shows a gradual reduction trend of about 10% per week over the last four to five weeks.

The Copernicus Atmosphere Monitoring Service (CAMS), implemented by the European Centre for Medium-Range Weather Forecasts on behalf of the European Commission, provides daily analyses of hourly concentrations of regulatory air pollutants, which can serve as “ground truth” to assess quantitatively and in more details the changes in concentrations identified from satellites and attributed to the effects of COVID-19 measures across the world.

The CAMS regional air quality analyses come in the form of hourly gridded maps and are obtained by combining satellite observations, surface in situ observations and numerical modelling. Taking the point covering the city of Milano, the hourly timeseries of surface concentration of NO2 since January 1st is shown below.

While no clear trend is visible over the first five weeks of the year, a decreasing trend can be seen starting during week 6 and continuing to date. Average NO2 concentrations were around 65 mg.m-3 in January, 45 mg.m-3 in February, and around 35 mg.m-3 for the first half of March. The linear decreasing trend on the daily average since week 6 is of the order of -4 mg.m-3 per week. Similar decreasing trends are found for other cities in Northern Italy, such as Torino or Bergamo. In the East, there seems to be rather a step change: in Bologna, concentrations were on average around 30 mg.m-3 in January and are on average around 15 mg.m-3 since the beginning of February (35 mg.m-3 and 15 mg.m-3 for Venezia).

“What the satellite observes is proportional to the vertically integrated amount of pollutants from the ground up to the top of the atmosphere”, explains Vincent-Henri Peuch, Director of Copernicus Atmosphere Monitoring Service. “This is quite different from the concentrations at the surface and even more so from the emissions. Given these limitations, it is quite remarkable that a signal of decreasing activity levels could be detected. This shows the extent of the measures taken by Italy.”

NO2 is a short-lived pollutant. Once emitted, it will stay in the atmosphere generally less than a day before being deposited or reacting with other gases. This means that this pollutant remains fairly close to where it has been emitted. Most of its emissions sources are located at the surface and are generated by human activities such as traffic, energy production, residential heating, industries, etc. The sources vary greatly during the day, as well as depending on the day in the week and the month. It also depends on factors such as weather, as a cold spell will trigger increased residential heating and energy demand.

CAMS is continually monitoring the air quality over Europe and on a global scale, providing the data to most leading websites and smartphone applications such as Windy, The Weather Channel, Breezometer or Plume Labs.

What is CAMS?

CAMS is implemented by ECMWF on behalf of the European Commission.
CAMS regional air quality analyses are operationally produced by a consortium of contractors led by Météo-France and INERIS (France). These partners rely on surface air quality observations provided by the European Environment Agency, which gathers them from each individual country.

The CAMS regional air quality analyses come in the form of hourly gridded maps and are obtained by combining satellite observations, surface in situ observations and numerical modelling that mimic the laws of physics and chemistry in the atmosphere. The data collected is of high quality and can be considered as “ground truth”. The main limitation of this dataset is that it cannot account for fine spatial variability and local effects that occur within a few meters to hundred meters near a source, like a road segment with heavy traffic or a power plant chimney stack. The data is representative of the average background values over a grid with a scale of 10km by 10km. The data can be obtained openly and freely from CAMS’ Atmosphere Data Store.

Can satellites really observe air pollution at the surface?

The European Commission’s Copernicus Sentinel-5 Precursor (S-5P) TROPOMI instrument benefits from an unprecedented spatial resolution of 3.5km x 5km, which allows to see fine maps of a number of air pollutants such as NO2. Satellite observations have however some limitations on the level of detail at which they can be used for monitoring air pollutants.

Firstly, they make their measurements from satellites in Low-Earth-Orbit and provide only one measurement per day for each location on Earth: for example, the overpass time of S-5P is 13:30 Mean Local Solar time. Second, the physics of the atmosphere is such that for pollutants like NO2, measurements are not possible or significantly degraded in the presence of clouds and of fine particles suspended in the air (aerosol). During the winter in Europe, this means that only about 25% of the data can be used.

To overcome this issue, observations can be averaged over longer periods of time (typically a running average of 10 days), in order to have at least one or two measurements for each location in each average period. Finally, and most importantly, what the satellite observes is proportional to the vertically integrated amount of pollutants from the ground and up to 10 km (tropopause); this is obviously different from the concentrations at the surface, let alone the emissions by human activities. Given these limitations, it is striking that a clear signal of decreasing activity levels could be detected. Over Europe, high-quality surface observations are made by each individual country and gathered by the European Environment Agency in Near-Real-Time. These observations can serve as “ground truth” to assess the reality of the signal detected by satellite.

What is the situation in other parts of Europe?

In other parts of Europe, the detection of statistically robust trend is yet more challenging, as shown below for some capitals in North-Western Europe. Weather-related episodes of high (between weeks 3 and 4; week 6) and low NO2 surface concentrations are the main features that can be seen.

What are the plans of Copernicus for monitoring emissions using satellites in the future?

As part of the Copernicus programme, CAMS is currently developing a capacity to derive emissions directly, using further advanced modelling techniques. An essential ingredient for this will be the new generation of satellites monitoring air pollutants. These will be embarked on geostationary platform and will provide hourly observations over selected part of the world.

The Korean Aerospace Research Institute’s Cheollian 2B satellite, which was launched into orbit aboard an Arianespace Ariane 5 rocket on February 18th, hosts the first instrument of this kind, GEMS (Geostationary Environment Monitoring Spectrometer); scientifically useful data covering parts of Asia is expected to be available at the end of this year. Similar instruments are planned over the US (TEMPO) and Europe. As part of Copernicus, the Sentinel-4 instrument onboard Eumetsat’s Meteosat Third Generation will launch in late 2022 or 2023. Sentinel-4 will be the backbone for the planned emissions information service of CAMS, which will be operated by ECMWF.

Valid: Thu 09 Apr 2020 06:00 to Fri 10 Apr 2020 06:00 UTC
Issued: Wed 08 Apr 2020 19:29
Forecaster: PUCIK

A level 2 was issued across eastern Iraq and western Iran mainly for large to very large hail and damaging wind gusts.

A level 1 was issued across Iraq, eastern Syria and southeastern Turkey mainly for large hail and severe wind gusts.

A level 1 was issued across eastern Algeria mainly for large hail and severe wind gusts.

SYNOPSIS

Stable weather conditions are forecast across much of western and central Europe under the influence of an extensive high pressure system centered over the Northern Sea. A cold front is forecast to cross the Baltic Sea and continue moving SE-wards across Poland, northern Ukraine and Belarus. Due to the dry conditions, the front will be mostly devoid of any precipitation.

More active weather pattern, at least concerning the convective storms, is forecast across southern parts of the forecast domain. Isolated to scattered storms are forecast ahead of an ill-defined trough over Spain and in northwesterly flow across northern Africa.

More widespread thunderstorms are anticipated over Turkey and parts of the Middle-East, under the influence of a deep mid-tropospheric low centered over Cyprus and southern Turkey.

DISCUSSION

SE Turkey, E Syria, Iraq and Iran

Ahead of the deep mid and upper tropospheric low, strong southwesterly flow is simulated over the region, increasing from southeastern Turkey towards Iran. Especially over Iraq, moist airmass combined with steep-lapse rates exceeding 7 K/km and 0-6 km shear around 25 m/s will create favorable conditions for severe convective storms. Given the strong shear, any initiating storm may become supercell with threat of large to very large hail and damaging wind gusts.

However, initiation remains questionable over the area of the best CAPE / shear overlap and NWP simulates only isolated storms. Thus, it seems that the hail threat will be more prominent than the wind gust threat.

Towards Iran and Turkey, models are more consistent regarding scattered to widespread initiation of the storms. Over Turkey, 0-6 km shear around 15 m/s will allow for multicells or some marginal supercells with threats of large hail or severe wind gusts.

E Algeria

Isolated to scattered storms are forecast in northwesterly flow, strongly increasing above 3 km. While 0-6 km shear will reach up to 25 m/s, 0-3 km shear will stay mostly below 10 m/s over the region.

Given EL mostly around 500 hPa and skinny CAPE profiles, it is questionable whether the shear confined to above 3 km will aid the storm organisation or mostly only enhance the dry air entrainment through the updrafts. At least few stronger updrafts may become well organised with primary threat of large hail and a low-end Lvl 1 is introduced.

Valid: Sat 04 Apr 2020 06:00 to Sun 05 Apr 2020 06:00 UTC
Issued: Fri 03 Apr 2020 20:35
Forecaster: GATZEN

• A level 1 has been issued across the Aegean Sea region mainly for excessive precipitation and large hail, tornadoes and severe wind gusts.

SYNOPSIS

A European polar trough is filled with cold and dry air masses that expand into most of the Mediterranean. A trough across the west Mediterranean moves east and starts to cut off as mid-level ridging increases across Central Europe. Ahead of the progressing Mediterranean trough, a strong south-westerly flow affects the Aegean and Turkey that turns south-east when the trough center passes late in the period.

DISCUSSION

An elevated mixed layer advects northward ahead of a cold front. At low levels, moisture is limited and given rather low temperature in the boundary layer, large CIN is present. However, along a mid-level front that moves eastward late in the period, weakening CIN is expected to extent into the moist air mass close to the cold front, and some weakly-capped CAPE can develop.

However, most CAPE will still be elevated as indicated by all available models. Therefore, chances of severe wind gusts and tornadoes are reduced.

Strong vertical wind shear is present along the cold front and overlaps with CAPE especially across the Aegean Sea. Curved hodographs indicate a good potential for rotating storms if sufficient boundary-layer rooting takes place.

Therefore, a few well-organized storms are not ruled out, capable of producing large hail. Severe wind gusts and tornadoes are not ruled out. Given the limitations discussed above, the overall potential is quite low, though.

Most significant severe weather threat will be excessive precipitation, though. To the north of the trough center, south-easterly flow advects moist air masses into the Aegean region. Latest models suggest neutral lapse rates, and non-convective precipitation is forecast, although some embedded storms may develop.

Main threat is along the western Aegean coasts due to upslope flow. Due to the mostly non-convective nature of precipitation, a level 1 has been issued.

Update: 13th of June 21:00 P.M. UTC

Tropical storm Nuri is located at 21.2N 112.8E, approximately 103 NM South-Southwest of Hong Kong and moving further towards the coast, which should reach in a several hours on Sunday.

Tropical typhoon warning has been issued as Hong Kong prepares to be disrupted by the cyclone.

The maximum sustainable winds are expected to be 63 km/h (34 KT) and gusts over 110 km/h (59 KT).

Update: 13th of June 12:00 P.M. UTC

Storm Nuri has formed in the Philippine Sea and later passed over the Luzon, Philippines on June 12th.

Nuri is now in South China Sea with a position at 20.0N 114.7E and travelling at speed 24 km/h (13 KT) past 6 hours.

Maximum sustainable wind speed is 64 km/h (35 KT) and gusts 83 km/h (45 KT).

Tropical storm Nuri is forecasted to make landfall this weekend 14th of June, to the southwest of Hong Kong, China.

https://www.windy.com/upload/5ee4c831b021b60012f27c5d?satellite,19.830,111.517,6,internal

Each model has a different update time and it could be confusing what connection does it have with the update time.

Here is the explanation:

• Reference time - is the time when a model starts a new forecast block.

It consists of:

Initialisation - data are entered into the model, this creates Initial conditions (initialisation time) and then model starts calculating conditions.
Assimilation - normalisation on data and assembling data for computation.
Computation - calculating the future atmospheric rates of change in time increments.
Data extraction - extracting data into regular forecast intervals.
Data storage - data are stored and written in accessible format.
Data postprocessing - special postprocessing routines

For example model ECMWF has an update interval 12 hours, that means the first reference time will be 00:00:00Z (Zulu time) and second one 12:00:00Z.

• Update time is time between the reference time and the actual update.
  The whole process of data computation takes approximately from 8 to 9 hours.

So for ECMWF model the update times are 07:15:00Z and 19:15:00Z.
See the exact update times here - When and how often are the weather data updated?.

Where to find info about reference and update time:

Desktop

App

@jpohorelicky Hi, Windy has been absolutely free for several years now, bringing a broad spectrum of new features every year for its users and creating a unique community of weather enthusiasts around the world. However as we gain more and more users, the costs of resources and infrastructure double every year, therefore we need to find sustainable income to keep going, such as every company needs to do. But as you can see, we didn't choose an option to make Windy a completely paid app nor we don't have any kind of advertisement like the majority of apps, instead we offer our contributors something extra and useful in return for their support.

One aspect of the COVID-19 pandemic has been a reduction in aircraft flights and thus of the aircraft-based observations available to weather prediction centres. The observations are used together with many others to help estimate the state of the Earth system at the start of forecasts.

At ECMWF, aircraft reports are second only to satellite data in their impact on forecasts. However, recently added satellite wind observations will help to mitigate the drop in the number of aircraft-based observations.

The reduction

The image below shows how the number of aircraft-based observations over Europe received and used at ECMWF has evolved since the start of March.

Number of aircraft reports over Europe received and used at ECMWF per day. Some reports are not used because they are near-duplicates, and a small proportion are rejected as poor quality. By 23 March there was a reduction of 65% in reports received compared to 3 March. Globally the reduction was about 42%.

One of the main sources of aircraft-based observations (ABOs) in operational weather forecasting is the WMO’s Aircraft Meteorological Data Relay (AMDAR) programme. The following two charts illustrate how the reduction in flights has affected European AMDAR reports.

European AMDAR coverage for 2 March 2020 (top) and 23 March 2020 (bottom). Colours indicate the altitude, with red indicating low altitudes. There is a general reduction in report density, particularly over Italy and parts of Eastern Europe. (Figures courtesy of Stewart Taylor, EUMETNET)

Many aircraft reports are provided by US airlines, with particularly dense coverage over the USA, but European and other programmes also make significant contributions. European aircraft reports, which are co-ordinated by EUMETNET, were particularly badly hit last week, but other programmes have declined substantially in the last few days.

To reduce costs, AMDAR reports may be switched off where there are already plenty of aircraft reports. This gives some resilience to the overall number of observations.

“The latest information available from airlines suggests that European AMDAR coverage will be reduced by 65% or more over the coming month, which is currently expected to continue into the summer,” says Steve Stringer, EUMETNET ABO Programme Manager.

The numbers and geographical coverage are also expected to be reduced elsewhere over the coming weeks.

“We are anticipating the substantial reduction in the availability of US AMDAR data to continue over the coming weeks, likely to generate some measure of impact on the output of our numerical weather prediction systems,” says Christopher Hill from the US National Oceanic and Atmospheric Administration (NOAA).

The Australian AMDAR programme has been normal up to now. “However, this is expected to change significantly soon, with Qantas suspending all international flights from the end of March and reducing Australian domestic flights by 60%,” says Douglas Body, from the Australian Bureau of Meteorology (BoM).

A small proportion of aircraft reports come from cargo flights, which are less affected than passenger flights.

The impact of aircraft observations at ECMWF

In 2019 a test was run: a series of forecasts without using aircraft reports (but with all other data) to estimate the state of the Earth system, compared to using all data (i.e. including aircraft reports).

As illustrated in the figure below, the largest impacts on forecasts are centred around 250–200 hPa (about 11–12 km in height), which is a typical aircraft cruising altitude. Geographically the largest impacts are in the northern hemisphere for both wind and temperature.

Impact of aircraft data on wind forecasts. The plots show the difference in vector wind root-mean-square (RMS) error between forecasts with and without aircraft observations, verified against ECMWF operational analyses (our best estimate of the state of the atmosphere based on all the available information). Yellow/red colours indicate worse forecasts without aircraft reports, and hatching indicates statistically significant differences at the 95% confidence level. The largest impacts are in the range up to 24-hours ahead, but a significant impact is seen in forecasts up to 7 days ahead.

As shown in the figure below, compared with radiosonde observations, 12-hour temperature forecasts in the northern hemisphere are more than 9% worse at cruise levels.

Impact on fit to radiosonde temperatures. The plot shows the impact of withholding aircraft-based observations on the quality of 12-hour temperature forecasts compared to radiosonde observations, in terms of the normalised difference in standard deviation. Values above 100% indicate bigger errors without aircraft-based observations.

“Removing half the aircraft reports would be expected to give slightly less than half the impact of removing all aircraft,” says ECMWF scientist Bruce Ingleby.

One estimate of how important different observations are is provided by the FSOI statistic (Forecast Sensitivity to Observation Impact). On this measure, aircraft observations provided 13% of the impact of all observations used at ECMWF averaged over 2019. About two thirds of this comes from aircraft wind observations.

The impact depends to some extent on the forecast system used. In their global forecasting systems, the Met Office (UK) sees about 8% of FSOI from aircraft data and NRL/FNMOC (USA) about 9%. Regional forecasting systems used by many European meteorological services also show a large impact from aircraft data.

In summary, the number of aircraft observations has gone down significantly over the last couple of weeks both over Europe and globally. In the coming days and weeks, we expect a further decrease in numbers, which will have some impact on forecast quality in the short range, particularly around the polar jet stream level (10–12 km altitude).

Sensitivity studies at ECMWF have shown that removing all aircraft data degrades the short-range wind and temperature forecasts at those levels by up to 15%, with significant degradations at all forecast ranges up to seven days. There is a smaller, but still statistically significant, impact on near-surface fields, up to 3% on surface pressure.

Mitigating the impact

Other types of observations are likely to be less affected by the COVID-19 disruption than aircraft reports, and there may be some additional radiosonde launches to try to mitigate the lack of aircraft data.

Satellite data provide a lot of information on temperature and humidity fields, but less on wind fields. In January 2020, ECMWF started using wind information from the Aeolus satellite.

“The Aeolus results demonstrate that there is still plenty of room to improve wind initial conditions,” says Lars Isaksen, the Head of the Actively Sensed Observations Group at ECMWF. “The Aeolus data will partly fill the gap due to fewer aircraft reports.”

Dear users,

in case you are having issues activating your Windy Premium subscription, please follow the steps below:

If you purchased on App Store or Google Store

1. Make sure you have the newest version of Windy, go to App/Google store and check there is no update, if yes, update it

2. Open Windy on a device, where you made the purchase, and log in with your Windy account, if you have not done so already

3. Initiate a window with subscription offer -> go to menu -> Windy Premium or click on the 1h forecast button in the detail of a certain location

4. Under the Monthly and Annual subscription options, you will find a button called 'Restore purchases'

5. Click the button

After clicking the button 'Restore purchases', you Windy Premium should be assigned to your account in case you have already bought it, but for some reason, it was not assigned.

If even this results in error, check you have a stable internet connection and try again. In case, you are still having troubles, contact us at support@windy.com and we will fix it. Please prepare your username.

If you subscribed via Desktop

1. Go to desktop and log in with your Windy account

2. Open the subscription offer window (e.g. click on the 1h forecast button in the detail of a certain location)

3. Click on 'Restore purchases'

3. On the next page, insert the subscription Order Reference code, you will find in your mail box

In case this option fails, please let us know your username and email, you made the purchase with at support@windy.com.

@nba Hello, I do not think there is something non-transparent in our communication. Windy has started as a DIY project of Ivo years ago. He had the idea and made it happen on his own and programmed the first version of Windy. Later he invited a few other colleagues to the project, but it was still a team of couple of people. Now, we are still a small team and we want to stay like that, we don't want to become a large company and loose the sense of what we do and what matters. Also, we stated, that the costs of infrastructure increase year by year, which is true and it is our biggest expense, so it is not a misinterpretation of any kind.

I understand there are always a mixed feelings, when a paid service is presented, but as mentioned, Windy remains free.

However it is important not to loose the message of this post, and it is to inform our users that COVID situation affected us and the launch itself too. Nevertheless, also to explain the background and reason for Windy Premium and how how our users may help.

Windy Webcams is another direction which has emerged from our endeavours of making the world even more accessible for everyone.

Our vision represents delivering access to thousands of webcams all over the globe capturing worlds places and giving you the opportunity to be informed by up-to-date images of a diverse locations. We are eager to connect webcam owners with users on one platform.

Webcams for users

Travel and have the world in the palm of your hand

• Look around and see what is happening
• See how it looks right now
• See how it looked in the past
• Explore beautiful locations from one spot
• Get a better idea about the weather conditions at the very moment
• Search for visual content by category, locations or description

Get your own API

You are interested in using webcams for your own website or App?

Have easy API access to thousands of webcams and be well-informed. Enhance your business with visual and authentic content and choose from the world's biggest inventory.

Implement your API and we will take care of the rest

• We add new webcams every day
• We test webcams regularly and handle inactive ones
• We check webcams quality
• We are in touch with webcams owners

Features

We keep things organised, all the webcams data is at one place and you are able to get webcams by -

• Category
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Find more information about options on Windy Webcams API

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Join the community and make your webcam go live for broad user audience with possibilities of an enormous reach.

For more details go to How to add a webcam and submit your application here

Valid: Fri 12 Jun 2020 06:00 to Sat 13 Jun 2020 06:00 UTC
Issued: Fri 12 Jun 2020 01:45
Forecaster: PISTOTNIK

• A level 1 and level 2 area issued for a large belt from SW Russia, the Ukraine, N Romania, Hungary, Slovakia, the Czech Republic, E Germany, Poland, Lithuania and Belarus mainly for large hail, excessive convective precipitation, severe convective wind gusts and to a lesser degree for tornadoes.

• A level 2 is issued for south-central France mainly for excessive convective precipitation and to a lesser degree for large hail, severe convective wind gusts and tornadoes.

• A level 1 was issued for S and E France mainly for excessive convective precipitation, large hail and to a kesser degree for severe convective wind gusts.

• A level 1 was issued for SE Romania, Bulgaria, N and central Turkey mainly for excessive convective precipitation and large hail.

• Level 1 was issued for NE Algeria, NW Tunisia and S Turkey for large hail and severe convective wind gusts.

Synopsis

A blocking pattern is in place. A large anticyclone over Scandinavia is opposed by an active cyclone over the Bay of Biscay and a filling mid-level low from the S Balkans to Turkey.

Very warm air from Russia is advected westward into E and central Europe at the northern flank of the cut-off lows.

Discussion

Northern Black Sea region, Poland and Germany

Similar to Thursday, the highest severe weather potential arises in the belt of maximized warm air advection, where low-level moisture accumulates to robust CAPE and synoptic lift works on the erosion of the (initially pronounced) capping inversion.

With expected dewpoints in the upper tens, CAPE between 500 to 1500 J/kg should be available again after some hours of daytime heating.

Vertical wind shear is rather weak with values around or below 10 m/s even across deep layers, but warm air advection creates veering low-level hodographs with moderately enhanced 0-3 km storm-relative helicity between 50 and 150 m^2/s^2.

All in all, this environment seems prime for some well-organized storms with a strong tendency to grow upscale and produce all kinds of severe weather, which was already confirmed by numerous severe weather events on Thursday (including hailstones up to 7 cm in size).

To the NE of this boundary, low-level moisture is expected to be shallow and vulnerable to thermal mixing processes, which should create dry and deeply mixed vertical profiles and reduce CAPE to a few hundred J/kg as soon as daytime heating takes over.

Hence this boundary will attain the characteristics of a dryline and will not only be the prime site of convective initiation, but also the northeastern margin of the area at the highest severe weather risk.

Under a pronounced cap and limited synoptic lift (aside from the ongoing warm air advection), convective initiation will happen rather late, possibly not before early to mid-afternoon, and may even completely fail across some areas. However, once it happens, it will likely set off a cascade of secondary initiations at outflow boundaries.

Best chances for the "convective nucleus" to form exist over and around Moldova, from where storms would likely move into N Romania and the SW Ukraine and possibly enter Hungary, Slovakia and Poland if they survive into the night.

In general, storms can contain embedded supercells and will quickly grow upscale into large clusters. The main risk at early stages is large to very large hail, followed by cold-pool-driven severe wind gusts and very heavy precipitation later on.

One or two brief tornadoes are not ruled out in case of favourably colliding gust fronts or outflow boundaries.
Signals for convective initiation are less convincing further eastward along the sea breeze front in the Ukraine and SW Russia and further northwestward towards central Europe.

Scattered storms can form over mountains in Romania, Slovakia, the Czech Republic and SW Poland, but may struggle against the cap once they detach from them.

A low-probability scenario, shown only by WRF, is a surviving overnight MCS over Hungary whose outflows could improve the chances for new storms on Friday also over flat terrain and further westward. However, at the time of writing (Thu 23 UTC), there are no indications for this outlier scenario to materialise.

In E and N Germany, stratus clouds will probably break up too late to allow surface-based storms already in the afternoon.

Chances for scattered storms to form or to move in from the Czech Republic and Poland increase in the evening and overnight, but they will likely be elevated and their severe weather risk is limited.

Poland, Kaliningrad, Lithuania, Belarus, Ukraine and Russia

Ahead of the western cut-off low, a few hundred J/kg CAPE in moist and moderately warm air overlap with strong vertical wind shear (15-20 m/s across the 0-3 km layer). Synoptic lift from a short-wave trough and frontal lift of a slowly advancing cold front across France will likely create scattered storms in the course of the day.

The highest severe weather risk evolves over south-central France, where constantly backbuilding storms originating from the Massif Central could create more than 100 mm rain within a few hours and produce a very dangerous flash flood situation (probably maximalized in the creeks discharging northwards).

With higher CAPE up to 1000 J/kg and enhanced 0-1 km shear under a southerly low-level jet, tail-end storms can contain mesocyclones with a risk of large hail, severe wind gusts or tornadoes.

Further north and east, the lower CAPE magnitude and the almost front-parallel storm motion limit the severe weather risk and shift it betimes to heavy rainfall. Convection will gradually become elevated and weaken in the evening and overnight while it spreads into BeNeLux, Germany and Switzerland.

Balkans and most of Turkey

Beneath the eastern cut-off low, scattered daytime-driven storms form in an environment of low to moderate CAPE and weak vertical wind shear. The main risks are heavy rain and localized marginally large hail.

Algeria, Tunisia and Turkey

Daytime heating of moist onshore and upslope circulations create some hundred J/kg CAPE, which overlap with enhanced vertical wind shear beneath the subtropical jet (up to 15 m/s in S Turkey, up to 25 m/s in Algeria and Tunisia).

Afternoon storms will stay isolated to scattered, but pose a main risk of large hail (especially with good access to coastal moisture) and severe downbursts (especially in the drier, more deeply mixed air further inland).