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    Štěpán Šubík

    @Štěpán Šubík

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    Best posts made by Štěpán Šubík

    • Beware of the Cumulonimbus capillatus

      As the last low-level cloud species will be Cumulonimbus capillatus (Cb cap), which is a really huge storm cloud. It is still counted as a low-level cloud because its base is usually below 2 km hight, but its top can reach the tropopause, which is about 10 km high in the middle latitudes and in equatorial areas it is about 16 km high. In extremes, the Cumulonimbus reaches the lower stratosphere at 20 km altitude. So, how does it look like, and why should we be careful?

      photo: Pxhere;
desc: Cumulonimbus capillatus storm cloud type low level.;
link: https://pxhere.com/en/photo/590124;
licence: cc

      Cumulonimbus capillatus looks like an anvil because it has a wide top which looks like a hair. And a word "hair" in Latin is "capillatus"! It sometimes remotely resemble a ruffled hair on a cloud, which can be long through all of the clouds. It is a nice look at it, but only from a distance.

      When it comes to precipitation, Cumulonimbus capillatus rarely causes showers. Usually, it makes heavy rain, thunderstorms, strong wind and hail. For all this, it is one of the most dangerous clouds you can spot in the sky!

      photo: Bidgee;
desc: Cumulonimbus capillatus storm cloud type low level.;
link: https://commons.wikimedia.org/wiki/File:Cumulonimbus_capillatus_3.jpg;
licence: cc

      Cumulonimbus is more likely to occur in summer and in some cases it comes with a cold front, rarely with a warm front.

      Watch out for the Cumulonimbus capillatus and send your photos!

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • How to recognize a cloud type?

      Have you ever looked at the sky and wondered what kind of clouds are there? In this and next episodes we will tell you about 10 basic types of clouds!

      At first, there are clouds right above our heads, so called low-level clouds, which are from the surface to 2,000 m (6,500 ft). These are Stratus, Stratocumulus and Cumulus.

      Higher we can find mid-level clouds, which are up to 7,000 m (23,000 ft). They are called Altostratus, Altocumulus and Nimbostratus, although Nimbostratus can have an extension into the lower level.

      The highest clouds are in the upper Troposphere, which ends around 12,000 m (40,000 ft). They are Cirrus, Cirrocumulus and Cirrostratus.

      
photo: commons.wikimedia.org;
link: https://commons.wikimedia.org/wiki/File:Cloud_types_en.svg;
licence: cc;
desc: Cloud classification, cloud types, according to WMO, according to height.;

      The last cloud is special, because it reaches from the low-level up to the high-level of the Troposphere and is called Cumulonimbus - the biggest beast among them.

      Next episodes will tell you more about them! We will open it with the most beautiful cloud - the Cumulus!


      23 January 2019

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • A cold spell will strike this weekend!

      Since Thursday, a cold spell has been cooling the whole of Europe except Spain. This weekend it will reach its maximum and warming is coming next week!

      A strong anticyclone above Scandinavia dictates the weather now. It brings cold air mass from Siberia and thus lower temperature (generally slightly above 0°C, in some places even under 0°C).

      weather forecast cold spell

      The anticyclone also blocks all cyclones and takes them northerly to west-northerly, so preventing from a big change in weather. For those reasons is possible to have the last ski weekend this winter.

      weather forecast cold spell

      The only warm European country will be Spain with a light touch of warm and cold fronts with temperatures around 0°C in the night and up to 18°C in the day. But on Sunday, the temperature will rise in all of Europe by ca 5°C.

      weather forecast cold spell

      Precipitation is expected in central Europe and the Balkan area. In mountains can be snow precipitation, but it will start melting. From next Wednesday we expect the temperature close to normal or higher.

      weather forecast cold spell

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      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Weather Phenomena: What's the difference between sustained winds and wind gusts

      A wind is the flow of air, formed by uneven heating of the earth's surface by the sun, usually from a high pressure-area to a low-pressure area. In the case of hurricanes or typhoons, ie. tropical cyclones, the wind is the most important physical quantity in the atmosphere.

      Wind can be measured by its speed and the direction of the flow. In the meteorology agencies’ warnings and advisories, or in the scientific papers and studies, the wind means (sustained) winds speed or it’s direction in the most cases, depending on the context.

      photo:Windy.com;desc:The picker on Windy’s wind forecast layer shows both, the direction and the (max. sustained) speed of the wind;licence:cc

      The hurricane, typhoon or cyclone warnings and advisories typically report maximal sustained winds and the gusts. What does maximum sustained wind speed and the wind gust mean? Let’s answer those questions.

      What is sustained wind speed

      Sustained winds (or simply winds) means winds sustained for a minimum time of at least 1 minute. Optimal mean wind speed is measured mostly for 1 to 15 minutes to avoid the influence of little turbulences in the atmosphere. Basic rule of thumb is that if not stated otherwise, the term max. sustained winds means maximum 10-minute sustained winds.

      What is the wind gust

      In meteorology, the wind is bounded with another quantity – the wind gusts, or simply gusts. Wind gusts are the highest immediate wind speeds measured in some time. That gives another point of view on the wind.

      Take Typhoon Kammuri (Tisoy in PAR) (seen below) as an example. On December 2nd at 6 p.m. UTC, typhoon Kammuri's maximum sustained winds were 105 kts km/h (194 km/h or 121 mph) with gusts of up to 130 kts (241 km/h or 150 mph). That means that the average wind speed was 194 km/h (121 mph), but for a few seconds in that one minute, the wind speed was at 241 km/h (150 mph).

      photo:JTWC/SATOPS;desc:Typhoon Kammuri over Philippines;

      Aside from how the wind is measured, another important metric that helps to determine or forecast cyclone’s intensity is the air pressure. Let’s get back to metrics of the wind itself.

      Wind direction and the track

      In the case of the tropical cyclone, which is rotating, another important item to forecast is its track and the extent of its winds. National meteorological agencies in the affected areas are issuing warning cones, typically once the storm intensifies at least to a tropical depression (learn more about the four stages of the tropical cyclones here). The cone shows the forecast track, the storm’s intensity (ie. tropical storm, hurricane, tropical depression), and the extent of the winds (radius).

      Even in the case of regular non-hurricane wind, it’s helpful to know its direction, or the track direction in the case of a cyclone. That’s typically reported in degrees or as an abbreviation, such as SW for southwest, NNE for north-north east, etc. The wind direction shown on Windy's picker can be set to degrees or an abbreviation in the Settings. Please note what's shown there is the direction of the wind, not the track (in the case of tropical cyclones).

      photo:Windy.com;desc:The picker's wind direction can be set to degrees or an abbreviation;

      Štěpán Šubík

      Prague based student of meteorology eager for science, who likes to learn, but also wants to live to the fullest every day. Follow me on Twitter.

      https://www.windy.com/-Satellite-satellite?satellite,7.787,115.115,6,internal

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Altocumulus - another nice cloud

      In the previous articles, we spoke about Nimbostratus and Altostratus which are not nice at all, so this time we will learn something about Altocumulus. Some say it is even more beautiful cloud than Cumulus! Let's find out.

      photo: pxhere;
desc: Altocumulus cloud classification middle level.;
link: https://pxhere.com/en/photo/1581403;
licence: cc;

      Altocumulus looks like balls, fluffs, rolls, ... just round masses. Many small round masses travelling together. It can be white, grey or both. And the rolls can be connected to each other or not. So you may now think it looks exactly like Stratocumulus. But the difference is that Altocumulus is higher in the sky and looks really smaller.

      photo: Grey Arsalian;
desc: Altocumulus cloud classification middle level.;
link: https://www.pexels.com/photo/ash-cloud-beautiful-clouds-blue-eyes-blue-sky-760691/;
licence: cc;

      While Altostratus can be observed just ahead of a warm front, Altocumulus usually comes right after a cold front and in the warm sector (between fronts) with 2-6 km (6.5 to 19.5 ft) altitude. Altocumulus is created when an upward stream has high humidity. Five different species are created by orography (mainly mountains).

      photo: pxhere;
desc: Altocumulus cloud classification middle level.;
link: https://pxhere.com/en/photo/1581363;
licence: cc;

      Altocumulus brings rarely precipitation and when it does, the rain does not reach the ground. This effect is called virga. When the water in those clouds freezes, halo effects can be observed.

      So next time we will discuss the Altocumulus species! Some of then can forecast an incoming storm!

      photo: He is sunny;
desc: Altocumulus cloud classification middle level.;
link: https://commons.wikimedia.org/wiki/File:A_Beautiful_cloud.jpg;
licence: cc;

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Nimbostratus - the second highest cloud

      Nimbostratus is the first mid-level cloud in our series, but you can evaluate it like a low-level cloud! Why? Let us find out!

      Nimbostratus is the second highest cloud. The highest (vertically most developed) is Cumulonimbus, that appeared in our previous article. Nimbostratus can reach 4 km (13 000 ft) in high and thousands of kilometres horizontally. Its base is below 3 km (10 000 ft) from the ground, and sometimes it can be created below 2 km (6 500 ft), which would make it a low-level cloud. But how does one look like?

      photo: Maurice Flesier;
desc: Nimbostratus mid level cloud type.;
link: https://commons.wikimedia.org/wiki/File:Nimbostratus_in_Istanbul.jpg;
licence: cc

      It is basically a thick grey or even darker layer. For its thickness, you cannot see Sun through it, which is the most notable difference between Nimbostratus and Stratus. Also, Nimbostratus is not so uniform and mainly causes persistent precipitation that cannot be associated with Stratus. But the precipitation can be caught in a layer above the ground and the rain can vaporize just before falling down on us.

      Nimbostratus occurs along a warm or occluded front, where warm air rises and the cloud is created just like cumulus, but in a way larger area. It can also appear from the transformation of Altostratus, Altocumulus or Cumulus.

      Nimbostratus can sometimes hide Cumulonimbus inside and therefore it can be associated with storms. There are special meteorological warnings for flights about the chances of thunderstorms in Nimbostratus and only meteorological radars can detect it for its detailed scan of the structure of clouds.

      Nimbostratus has no species and even no varietes.

      photo: LivingShadow;
desc: Nimbostratus mid level cloud type.;
link: https://commons.wikimedia.org/wiki/File:Nimbostratus_virga_grey_with_hills.jpg;
licence: cc

      Have you seen this big boy? Send your photos!

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Altocumulus stratiformis is the most frequent species

      As we wrote about Altocumulus, we must mention all of its species. The first to come is Altocumulus stratiformis (Ac str).

      photo: GerritR;
desc: Altocumulus stratiformis cloud classification mid-level.;
link: https://commons.wikimedia.org/wiki/File:Altocumulus_stratiformis_perlucidus_undulatus_virga.jpg;
licence: cc;

      Altocumulus stratiformis consists like any other Altocumulus of small fluffs in the shape of round clouds. It is the thinnest Altocumulus. But the main difference is that the little clouds form lines and spaces. It all looks like sheep in a military formation marching through the sky.

      photo: Wdwdbot;
desc: Altocumulus stratiformis cloud classification mid-level.;
link: https://de.m.wikipedia.org/wiki/Datei:Wolkenformation_Bonn-Kessenich_201610231510.jpg;
licence: cc;

      It is not a surprise to observe a Virga with this species - precipitation that evaporates before it reaches the ground. And also this species can cover a few thousands of kilometres squared in the sky.

      Altocumulus stratiformis typically indicate a change in the weather either from sunny weather to more unstable conditions or it can be the last part of bad weather on a cold front.

      photo: GerritR;
desc: Altocumulus stratiformis cloud classification mid-level.;
link: https://commons.wikimedia.org/wiki/File:Altocumulus_stratiformis_undulatus_translucidus_perlucidus_radiatus_über_Edinburgh.jpg;
licence: cc;

      So what about another species? See in the next articles!

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Is it UFO or Altocumulus Lenticularis?

      Altocumulus lenticularis is a lens-shaped cloud that forms in mountains or hilly areas. It is created just like Stratocumulus lenticularis. When moist air rises up, a cloud is created due to lowering the pressure and thus condensation of the moist air into droplets. And when this process is creating the cloud, surrounding hills or mountains can affect its shape and lenticular cloud type is created.

      Photo: Marc Veraart;
desc: Altocumulus lenticularis cloud type classification.;
link: https://www.flickr.com/photos/marcveraart/4723153673/;
licence: cc;

      Unlike Stratocumulus lenticularis, Altocumulus lenticularis is not connected with any precipitation except virga and it looks smaller because of its distance.

      Photo: JotaCartas;
desc: Altocumulus lenticularis cloud type classification.;
link: https://commons.wikimedia.org/wiki/File:Lenticular_clouds_(Altocumulus_lenticularis)_(30368465690).jpg;
licence: cc;

      In conclusion, Altocumulus lenticularis has a very special shape. It is also the most common cloud species mistaken for UFO. It can be roundish and it can have sharp edges so in some light from some ankle it looks just like UFO.

      Photo: NOAA Photo Library;
desc: Altocumulus-lenticularis-cloud-type-classification.;
link: https://www.photolib.noaa.gov/htmls/wea00010.htm;
licence: cc;

      Have you ever seen this wonder in the sky? Send your photos!

      Photo: Mike Lewinski;
desc: Altocumulus lenticularis cloud type classification.;
link: https://www.flickr.com/photos/ikewinski/8692246016;
licence: cc;

      Photo: Walter Baxter;
desc: Altocumulus lenticularis cloud type classification.;
link: https://www.geograph.org.uk/photo/3549467;
licence: cc;

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Cumulonimbus - the biggest beast it the sky

      The last cloud type in the low-level troposphere is Cumulonimbus, the highest cloud. How can we recognize it and most importantly what does it mean when Cumulonimbus is coming our way?

      Cumulonimbus is a heavy and dense cloud that can reach from the low level up to the high-level troposphere (from 1 km to 12 km). It is a white and grey massive cloud tower with smooth, fibrous or striated parts of its upper portion. The base is often really dark and bad looking at all.

      photo: jacinta lluch valero;
link: https://www.flickr.com/photos/70626035@N00/15115948415;
desc: Cumulonimbus cloud type a low level cloud.;
licence: cc
      Image credits: jacinta lluch valero

      Usually, the Cumulonimbus brings heavy rain that can last for hours! And there's more! Cumulonimbus is responsible almost for every thunderstorm, tornados and other dangerous phenomenona. So, when you see it, find yourself a good shelter, stay at home or hide in a bar.

      Have you seen the Cumulonimbus at its best? Send your photos!

      photo: Piyapon Poottima;
link: https://www.pexels.com/photo/before-rain-cb-cloud-cumulonimbus-573949/;
desc: Cumulonimbus cloud type a low-level cloud.;
licence: cc
      Image credits: Piyapon Poottima

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • What is a tropical cyclone

      A tropical cyclone is a low-pressure place in the atmosphere located near the equator. It can be recognized by its structure and origin.

      Tropical cyclones have an unquestionable impact on the lives of people living in the tropics. But why do they appear only in certain places and how are the tropical cyclones formed in the first place?

      photo: NASA’s Aqua satellite;
desc: Tropical cyclone Winston;
link: https://en.wikipedia.org/wiki/List_of_retired_South_Pacific_cyclone_names#/media/File:Winston_2016-02-20_0130Z_(cropped).jpg;
licence: cc;

      How tropical cyclones are formed

      Tropical cyclones can be formed only in the tropics because they need a huge amount of energy, which can be present only in the tropics above an ocean when six conditions are satisfied:

      1. Temperature – the temperature of the ocean must be above 26 °C (79 °F). This condition leads to strong evaporation of the oceanic water and the water vapour is the most important source of energy for the hurricanes through its condensation.

      2. Distance from the equator – the hurricane cannot be created right on the equator. Hurricanes need some force to start it's spinning and that force is the Coriolis force. Coriolis force is zero on the equator and rises when moving towards the poles. That is why hurricanes can’t be present within 5 degrees latitude.

      3. Saturated lapse rate gradient near its centre – for the efficiency of using energy. When water vapour is present in the centre of the cyclone, it condensates and releases latent heat at a maximum rate due to a saturated lapse rate.

      4. High relative humidity – for evaporated water and avoiding trade wind inversion. Trade wind inversion means subsidence of air mass which is present mainly in anticyclones. That destroys cyclones. And evaporated water must be present, but with low humidity, the ocean evaporates more and its temperature decreases and can drop below the condition one temperature.

      5. Low vertical wind shear – a low difference of wind speed and direction vertically. If there is a strong wind in the upper atmosphere or in the opposite direction, the tropical cyclones won’t form in the upper levels and will lose energy quickly.

      6. Final condition is the presence of a tropical wave. It can be any disturbance in the atmosphere, for example, a thunderstorm that moves off the coast of Africa to the east.

      When all these conditions are met, a tropical cyclone is created.

      photo: NASA;
desc: Hurricane Florence;
link: https://www.flickr.com/photos/gsfc/42828604840;
licence: cc;

      Moreover, we can distinguish between two types of cyclones - tropical and extratropical. A subtropical cyclone is something in between.

      Tropical cyclones are created a few degrees from the equator and are quite small on the horizontal scale. They are deeper, which means that there is a bigger gradient of pressure. They cannot have any frontal system and they move from east to west because they are pushed by the trade winds flowing close to the equator.

      In their centre, tropical cyclones are warm because they collect energy from condensing water droplets and the process of condensation means warms the surrounding air.

      Tropical cyclones are dangerous because of its huge energy hidden in water vapour that can release its potential by condensation and the heat can be transformed to lower pressure causing really strong winds capable of taking even cars and houses.

      When a tropical cyclone is fully developed, with its eye, eyewall, wind speed above 74 mph (119 km/h), it is classified depending mainly on the wind speed and its location as a hurricane, typhoon or simply cyclone.

      photo: David Hayden;
desc: Tropical cyclone;
link: http://www.restaurantlaughs.com/wp-content/uploads/2011/02/perfect-storm.jpg;
licence: cc;

      Before we get to hurricanes and typhoons, we’ll examine the anatomy of the tropical cyclone. See you in the next chapter soon.

      Next chapters:

      • Four stages of Tropical Cyclone. From Tropical Disturbance to a Hurricane
      • What is the difference between tropical and extratropical cyclone
      • What’s the difference between hurricane, typhoon, cyclone

      Previous chapters:

      • What is a cyclone
      posted in Articles
      Štěpán Šubík
      Štěpán Šubík

    Latest posts made by Štěpán Šubík

    • Weather Explained: What’s the difference between a hurricane, typhoon, cyclone and tornado

      In the previous article, we mentioned the differences between extratropical and tropical cyclones. But what is the difference between hurricane, typhoon, cyclone and tornado?

      Hurricane, typhoons and cyclones are just different names for the same objects. They all mean tropical cyclone, but historically the cyclones are distinguished by the region of appearance. It is an object in the atmosphere which has very low pressure in its centre and therefore causes the wind to spin around.

      What is a tornado?

      Tornado is a phenomenon which appears in convective storms mostly in supercells. it is created differently than the tropical cyclone. It forms from a downburst in a storm when cold air subsides and warm air rises from the Earth. Tornado is even smaller and lasts not as long as a cyclone.

      What direction hurricane spins

      Hurricane is widely known for its destructive power. The destruction is mainly caused by its winds speed, which reaches 74 mph (119 km/h) and more. The casualties caused by tropical cyclone going from ocean to land depend on the orography of the coast and direction of the wind circling around its centre. So, what direction does a hurricane spins?

      Hurricane or a tropical cyclone is a low-pressure object in the atmosphere. Simply said, the centre has the lowest pressure and therefore the wind should go straight from the edge to the centre. This could be true only if the Earth doesn’t spin. Since the Earth rotates every 24 hours around its axis, we must add physics in a form of Coriolis force to our little model.

      Coriolis force is a force that affects only those particles that move in a system that is moving itself. Even when you walk down the street, the Coriolis force is present, but it is small due to slow movement and friction. On the northern hemisphere, the Coriolis force causes all particles to change the direction of movement slightly to the right, on the southern hemisphere, to the left.

      Adding the Coriolis force to our little model, the wind on the northern hemisphere will be moving still radially from the edge to the centre of the cyclone, but it will also turn right (in the southern it’s to the left). The little deviation in the motion causes the wind in the northern hemisphere to circle anticlockwise and in the southern hemisphere to circle clockwise.

      photo:Windy.com;desc:Anatomy of a hurricane; licence:cc;

      Where do hurricanes form

      Hurricane is a name for tropical cyclones in the Atlantic Ocean and north-eastern Pacific Ocean. The Hurricanes in the Atlantic Ocean form close to the shores of Africa. The best place there is near Sahara where are extreme differences between hot and dry desert and colder and humid ocean. There are common waves in the atmosphere too, which is one of the seven conditions needed to form a tropical cyclone.

      In the north-eastern Pacific Ocean, the hurricanes form near the west shores of Middle America (from Panama to Mexico) or can be once again strengthened hurricane from the Atlantic. They all head westerly and therefore they usually end in the Pacific Ocean. They can in rare situations turn back when going northerly and reaching the westerlies.

      And there is one interesting fact to add. The English word “hurricane“ originates in Mayan god of wind, storm and fire “huracán“. The Carib Indians took the name and gave it to their god of evil, “huricán“. And then the Spanish came and turned it back into “huracán“, which is a Spanish word for a hurricane since then. The last modification was in the 16th century by the English to “hurricane“.

      Where do typhoons form

      In the north-western Pacific Ocean basin, tropical cyclones are called typhoons. They all form in the North Pacific Ocean a few degrees from the Equator and goes as usually all tropical cyclones westerly. The typhoons can move slightly to the north and sometimes they reach westerly winds that cause the typhoons to move back to the east. The returning cyclones disappear in the Pacific and causes.

      photo:Windy.com;Typhoon Hagibis over Western Pacific;licence:cc;

      The reason for naming the cyclones “typhoons” and not “hurricanes” was linguistic. The word “typhoon“ has a bit of difficult origin. It is thought to be old Mandarin Chinese word for big wind “dàfēng“ that evolved through Cantonese word “daai fung“ to Hakka “thai-fûng“ and then to modern common known word “typhoon“. But it is quite interesting that an ancient Greek name for the father of winds is “Tuphôn“. Do you think they could have an impact on the word or is it just coincidence?

      South Pacific and Indian Ocean: Simply a cyclone

      In South Pacific, Cyclone is mostly used the name for tropical cyclones or cyclonic storms. The cyclones form in the South Pacific Ocean a few degrees away from the Equator and move to the west mostly threatening Australia.

      In the Indian Ocean, the Cyclones form in the Bay of Bengal again a few degrees from the Equator and moves westerly or northerly.

      photo:Windy.com;desc:Tropical Cyclone Ambali over Indian Ocean;licence:cc

      The term “Cyclone” is a simply short version of words “Tropical Cyclone”. And the word “Cyclone” has a straight origin. It comes from Greece, where the word for “moving in a circle” is “kyklos“.

      Štěpán Šubík

      Prague based student of meteorology eager for science, who likes to learn, but also wants to live to the fullest every day. Follow me on Twitter.

      https://www.windy.com/-Satellite-satellite?satellite,internal

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Weather Explained: What is the difference between tropical and extratropical cyclone

      The meteorologists distinguish cyclones by the speed of their movement on stationary (moving slowly or not at all) and nonstationary (moving fast) which helps in the weather forecast.

      Another common way to differ between cyclones is by dividing them in two groups. Tropical and extratropical cyclones.

      What is extratropical cyclone

      Extratropical cyclones are created usually around polar jet and they are quite large in a horizontal scale. They usually have their own frontal system with a warm front, cold front and warm sector. These cyclones move from west to east because they are in regions with the westerly flow (ca 30° - 60° in latitude). In their centre, they are cold as they form in middle latitude.

      Tropical cyclone

      On the other hand, tropical cyclones are created a few degrees from the equator and are quite small in horizontal scale, but deeper, which means that there is a bigger gradient of pressure and lower pressure in its centre. They cannot have any frontal system and they move from east to west because they are pushed by the trade winds around the equator. In their centre, they are warm because they collect energy from condensing water droplets and the process of condensation means warming the surrounding air.

      Štěpán Šubík

      Prague based student of meteorology eager for science, who likes to learn, but also wants to live to the fullest every day. Follow me on Twitter.

      Next chapters:

      • What’s the difference between hurricane, typhoon, cyclone and tornado

      Previous chapters:

      • What is a cyclone
      • What is a tropical cyclone

      https://www.windy.com/-Satellite-satellite?satellite,internal

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Weather Phenomena: What's the difference between sustained winds and wind gusts

      A wind is the flow of air, formed by uneven heating of the earth's surface by the sun, usually from a high pressure-area to a low-pressure area. In the case of hurricanes or typhoons, ie. tropical cyclones, the wind is the most important physical quantity in the atmosphere.

      Wind can be measured by its speed and the direction of the flow. In the meteorology agencies’ warnings and advisories, or in the scientific papers and studies, the wind means (sustained) winds speed or it’s direction in the most cases, depending on the context.

      photo:Windy.com;desc:The picker on Windy’s wind forecast layer shows both, the direction and the (max. sustained) speed of the wind;licence:cc

      The hurricane, typhoon or cyclone warnings and advisories typically report maximal sustained winds and the gusts. What does maximum sustained wind speed and the wind gust mean? Let’s answer those questions.

      What is sustained wind speed

      Sustained winds (or simply winds) means winds sustained for a minimum time of at least 1 minute. Optimal mean wind speed is measured mostly for 1 to 15 minutes to avoid the influence of little turbulences in the atmosphere. Basic rule of thumb is that if not stated otherwise, the term max. sustained winds means maximum 10-minute sustained winds.

      What is the wind gust

      In meteorology, the wind is bounded with another quantity – the wind gusts, or simply gusts. Wind gusts are the highest immediate wind speeds measured in some time. That gives another point of view on the wind.

      Take Typhoon Kammuri (Tisoy in PAR) (seen below) as an example. On December 2nd at 6 p.m. UTC, typhoon Kammuri's maximum sustained winds were 105 kts km/h (194 km/h or 121 mph) with gusts of up to 130 kts (241 km/h or 150 mph). That means that the average wind speed was 194 km/h (121 mph), but for a few seconds in that one minute, the wind speed was at 241 km/h (150 mph).

      photo:JTWC/SATOPS;desc:Typhoon Kammuri over Philippines;

      Aside from how the wind is measured, another important metric that helps to determine or forecast cyclone’s intensity is the air pressure. Let’s get back to metrics of the wind itself.

      Wind direction and the track

      In the case of the tropical cyclone, which is rotating, another important item to forecast is its track and the extent of its winds. National meteorological agencies in the affected areas are issuing warning cones, typically once the storm intensifies at least to a tropical depression (learn more about the four stages of the tropical cyclones here). The cone shows the forecast track, the storm’s intensity (ie. tropical storm, hurricane, tropical depression), and the extent of the winds (radius).

      Even in the case of regular non-hurricane wind, it’s helpful to know its direction, or the track direction in the case of a cyclone. That’s typically reported in degrees or as an abbreviation, such as SW for southwest, NNE for north-north east, etc. The wind direction shown on Windy's picker can be set to degrees or an abbreviation in the Settings. Please note what's shown there is the direction of the wind, not the track (in the case of tropical cyclones).

      photo:Windy.com;desc:The picker's wind direction can be set to degrees or an abbreviation;

      Štěpán Šubík

      Prague based student of meteorology eager for science, who likes to learn, but also wants to live to the fullest every day. Follow me on Twitter.

      https://www.windy.com/-Satellite-satellite?satellite,7.787,115.115,6,internal

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Four stages of Tropical Cyclone. From Tropical Disturbance to a Hurricane

      photo:Windy.com;desc:Typhoon twins Lekima and Krosa;licence:cc;

      If the six conditions, we’ve covered in previous chapter, are met, the tropical cyclone appears. Let's now learn what phases there are to grow from the tropical disturbance of the atmosphere to a huge tropical cyclone.

      It starts with a tropical disturbance

      At the beginning of every tropical cyclone, there is a tropical disturbance or a wave that can be caused for example by thunderstorm going from a land above an ocean. In this phase, previously mentioned six conditions play a big role to start the engine of development.

      What is a tropical depression

      In the next phase, the wind rises and starts to circle a centre of the disturbance due to the Coriolis force. Now it’s called tropical depression and it is a measurable and observable object in the atmosphere with clouds slightly rotating around causing low precipitation.

      Almost a Hurricane

      When the wind speed reaches 39 mph (63 km/h), it is called a tropical storm. Tropical storm looks like a little hurricane, but it has no eye in its centre. It is all covered in clouds spinning around an invisible centre.

      In this phase, the storm gets a name. It can stop growing here and the name will be already used for only tropical storm and not for a cyclone (like was a case with recent tropical storm Ivo that weakened to tropical depression). More on tropical storm naming in following chapters. Anyway, even tropical storms can make huge damage.

      When Tropical storm becomes a Hurricane

      Finally, tropical cyclone is a phase with wind speed above 74 mph (119 km/h). It has a fully developed eye in the centre and its structure is quite stable above an ocean.

      There are different names for tropical cyclones based on location, they are called hurricanes in the Atlantic Ocean and north-eastern Pacific Ocean, typhoons in the north-western Pacific Ocean and simply cyclones in South Pacific and Indian Ocean.

      Before we get to more details in the upcoming chapters, we’ll uncover the difference between tropical and extratropical cyclone in the next one. See you next chapter.

      Štěpán Šubík

      Prague based student of meteorology eager for science, who likes to learn, but also wants to live to the fullest every day. Follow me on Twitter.

      Next chapters:

      • What is the difference between tropical and extratropical cyclone
      • What’s the difference between hurricane, typhoon, cyclone

      Previous chapters:

      • What is a cyclone
      • What is a tropical cyclone

      https://www.windy.com/-Satellite-satellite?satellite,29.037,-46.758,4,internal

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • What is a tropical cyclone

      A tropical cyclone is a low-pressure place in the atmosphere located near the equator. It can be recognized by its structure and origin.

      Tropical cyclones have an unquestionable impact on the lives of people living in the tropics. But why do they appear only in certain places and how are the tropical cyclones formed in the first place?

      photo: NASA’s Aqua satellite;
desc: Tropical cyclone Winston;
link: https://en.wikipedia.org/wiki/List_of_retired_South_Pacific_cyclone_names#/media/File:Winston_2016-02-20_0130Z_(cropped).jpg;
licence: cc;

      How tropical cyclones are formed

      Tropical cyclones can be formed only in the tropics because they need a huge amount of energy, which can be present only in the tropics above an ocean when six conditions are satisfied:

      1. Temperature – the temperature of the ocean must be above 26 °C (79 °F). This condition leads to strong evaporation of the oceanic water and the water vapour is the most important source of energy for the hurricanes through its condensation.

      2. Distance from the equator – the hurricane cannot be created right on the equator. Hurricanes need some force to start it's spinning and that force is the Coriolis force. Coriolis force is zero on the equator and rises when moving towards the poles. That is why hurricanes can’t be present within 5 degrees latitude.

      3. Saturated lapse rate gradient near its centre – for the efficiency of using energy. When water vapour is present in the centre of the cyclone, it condensates and releases latent heat at a maximum rate due to a saturated lapse rate.

      4. High relative humidity – for evaporated water and avoiding trade wind inversion. Trade wind inversion means subsidence of air mass which is present mainly in anticyclones. That destroys cyclones. And evaporated water must be present, but with low humidity, the ocean evaporates more and its temperature decreases and can drop below the condition one temperature.

      5. Low vertical wind shear – a low difference of wind speed and direction vertically. If there is a strong wind in the upper atmosphere or in the opposite direction, the tropical cyclones won’t form in the upper levels and will lose energy quickly.

      6. Final condition is the presence of a tropical wave. It can be any disturbance in the atmosphere, for example, a thunderstorm that moves off the coast of Africa to the east.

      When all these conditions are met, a tropical cyclone is created.

      photo: NASA;
desc: Hurricane Florence;
link: https://www.flickr.com/photos/gsfc/42828604840;
licence: cc;

      Moreover, we can distinguish between two types of cyclones - tropical and extratropical. A subtropical cyclone is something in between.

      Tropical cyclones are created a few degrees from the equator and are quite small on the horizontal scale. They are deeper, which means that there is a bigger gradient of pressure. They cannot have any frontal system and they move from east to west because they are pushed by the trade winds flowing close to the equator.

      In their centre, tropical cyclones are warm because they collect energy from condensing water droplets and the process of condensation means warms the surrounding air.

      Tropical cyclones are dangerous because of its huge energy hidden in water vapour that can release its potential by condensation and the heat can be transformed to lower pressure causing really strong winds capable of taking even cars and houses.

      When a tropical cyclone is fully developed, with its eye, eyewall, wind speed above 74 mph (119 km/h), it is classified depending mainly on the wind speed and its location as a hurricane, typhoon or simply cyclone.

      photo: David Hayden;
desc: Tropical cyclone;
link: http://www.restaurantlaughs.com/wp-content/uploads/2011/02/perfect-storm.jpg;
licence: cc;

      Before we get to hurricanes and typhoons, we’ll examine the anatomy of the tropical cyclone. See you in the next chapter soon.

      Next chapters:

      • Four stages of Tropical Cyclone. From Tropical Disturbance to a Hurricane
      • What is the difference between tropical and extratropical cyclone
      • What’s the difference between hurricane, typhoon, cyclone

      Previous chapters:

      • What is a cyclone
      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • What is a Cyclone

      In simple words, a cyclone is a type of storm with winds spiralling inwards, or more precisely - like a meteorologist - would tell you, the cyclone is low-pressure structure in the atmosphere.

      Pressure in the atmosphere is not the same in every place and it even changes in time. There are places with lower pressure called cyclones and places with higher pressure named anticyclones.

      In cyclones, there is the pressure between 900 and 1020 hPa (in extremes a few hPa below 900 hPa) which is lower than the pressure around, so the air tries to get to its centre. The winds would aim straight to the centre of a cyclone if there was no Coriolis force.

      In the large scale weather systems, we can distinguish between three main types of surface-based cyclones: Extratropical cyclones, Subtropical cyclones and Tropical cyclones. In the mesoscale weather systems category, we can find cyclones too. Tornado, waterspout, dust devil or firenado are just a few examples of them.

      Now let’s get back to large-scale weather systems.

      photo: B dash;
desc: Cyclone Idai above Madagascar;
link:https://upload.wikimedia.org/wikipedia/commons/0/02/Cyclone_Idai_west_of_Madagascar.jpg;
licence: cc;

      What direction cyclone spins

      Coriolis force makes every particle which is moving on the Earth to slightly turn from its direction. In the Northern hemisphere, it is to the right and in the Southern hemisphere, it is to the left. That is why the wind turns around a cyclone anticlockwise in the Northern hemisphere and clockwise in the South.

      photo: bniegel;
desc: A cyclone - tropical storm Lee;
link: http://www.dodlive.mil/2012/09/01/hurricane-hunters-provide-critical-data/tropical-storm-lee/;
licence: cc;

      To be continued… Next chapters:

      • What is a tropical cyclone
      • The anatomy of the tropical cyclone
      • What is the difference between tropical and extratropical cyclone
      • What’s the difference between hurricane, typhoon, cyclone
      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Altocumulus volutus is a four-leaf clover in the sky

      As we wrote about Altocumulus and its species, the rarest is Altocumulus volutus. It is very lucky to see this species above our heads.

      photo: Joe Thomissen;
desc: altocumulus-cloud-mid-level-rare-cloud-type;
link: https://www.flickr.com/photos/thomissen/5889349440;
licence: cc;

      Altocumulus volutus is quite like Stratocumulus volutus. That means a long, horizontal, detached, tube-shaped cloud mass which often appears to roll slowly about a horizontal axis. Unlike Stratocumulus, Altocumulus volutus is usually a single line and, like it is with the mid-level clouds, it appears smaller.

      photo: pxhere;
desc: altocumulus-cloud-mid-level-rare-cloud-type;
link: https://pxhere.com/en/photo/1197649;
licence: cc;

      Photos of Altocumulus volutus are very rare even though it is a beautiful cloud that is not connected with precipitation. If you have seen one, send us your photos!

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • How to recognize upcoming storm? Look for Altocumulus castellanus

      Among all of the Altocumulus cloud species, Altocumulus castellanus has the greatest impact on the weather forecast. So how to recognize it?

      photo: Ralph W. lambrecht;
desc: Storm and tornado - bad weather.;
link: https://www.pexels.com/photo/lightning-and-tornado-hitting-village-1446076/;
licence: cc;

      Altocumulus castellanus (Ac cas) is a mid-level cloud with its base from 2 km (6,500 ft) up to 6 km (20,000 ft). They are very similar to Stratocumulus castellanus and the main difference is that they look smaller and there is no precipitation connected to them.

      photo: Bidgee;
desc: Altocumulus castellanus cloud type.;
link: https://commons.wikimedia.org/wiki/File:Altocumulus-Castellanus.jpg;
licence: cc;

      But Altocumulus castellanus is a big help in predictions of incoming heavy showers or thunderstorms. Ac cas is created when a mid-level instability appears. If surface-based convection can connect to the mid-level instability, Ac cas can transform into Cumulonimbus clouds.

      photo: Daniele.Brundu;
desc: Altocumulus castellanus cloud type.;
link: https://commons.wikimedia.org/wiki/File:Altocumulus_castellanus.jpg;
licence: cc;

      Have you ever seen this phenomenon? Send us your photos!

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • Víkend přináší naději na úrodu, sucho si začíná vybírat svou daň

      Sucho trápí Česko už několik let v řadě. Pro naše území jsou typické letní srážky, které jsou četnější i intenzivnější než zimní. Několik let v řadě však téměř chyběly.

      Pro zemědělství je dostatek vláhy důležitým předpokladem pro dobrou úrody. Se snižujícími se zásobami podzemních vod roste ohrožení úrody. O víkendu proto přijdou vítané srážky, které by měli pomoct rostlinám v jejich nejnáročnějším období.

      photo: CHMU;
desc: Zasoba vyuzitelne vody v profilu lehke pudy 2019;
link: http://portal.chmi.cz/files/portal/docs/meteo/ok/SUCHO/zvvp_lp_srov.html;

      V pátek po řadě slunných dní, kdy se Česko nacházelo v teplém sektoru frontálního systému, začne naše území přecházet zvlněná studená fronta, která sníží teplotu v průměru o 10°C a s sebou přinese nejen déšť, ale i bouřky, hlavně na západě našeho území.

      photo: Windy;
licence:cc;

      Srážky budou na hraničních horách narůstat a dostanou se v průběhu soboty nad celé Čechy, za Českomoravskou vrchovinou se budou vyskytovat jen výjimečně. Na obrázku je oranžově vyznačena oblast největšího deficitu využitelné vody v profilu lehké půdy pod travním porostem, tedy oblast, kde zásoba vody tvoří méně než 25% průměru z let 1961 až 2010, počítáno v pondělí 22. 4. 2019.

      pict: Windy;
desc: 2019 04 25 forecast;
licence:cc;

      V sobotu se budou srážky vyskytovat hlavně na horách na západě a na Vysočině, ojediněle v nížinách. Tyto situace model často nadhodnocuje a proto ne v každém modře vyznačeném území bude pršet. Srážky se vzácně mohou dostat na Olomoucko přes Orlické hory.

      photo: Windy;
licence:cc;

      Koncem víkendu bude srážek ubývat, mohou se však začít objevovat v Beskydech. Původcem srážek za studenou frontou bude vyplňující se tlaková níže na západě Německa, která přináší vítr ze západu až jihozápadu.

      ![photo: Windy;
      licence:cc;]
      (https://community.windy.com/assets/uploads/files/1556221327379-annotation-5cc20d8a965c1b001b5c828b.jpg)

      Počátkem příštího týdne je zmíněná níže již zcela zaplněna a níže nad Polskem od nás odsune zbytek srážek ze zaniklé níže.

      photo: Windy;
licence:cc;

      V úterý se nad naše území dostane opět déšť a můžeme jen doufat, že jej bude dostatek.

      pict: Windy;
licence:cc;

      https://www.windy.com/annotation/5cc20866dbae29001b647b1f

      https://www.windy.com/annotation/5cc20aeb965c1b001b5c8289

      https://www.windy.com/annotation/5cc20c0e965c1b001b5c828a

      https://www.windy.com/annotation/5cc20d8a965c1b001b5c828b

      https://www.windy.com/annotation/5cc20dee965c1b001b5c828c

      https://www.windy.com/annotation/5cc20eb9965c1b001b5c828d

      posted in Articles
      Štěpán Šubík
      Štěpán Šubík
    • RE: Your map annotations

      2019_04_25-utery

      https://www.windy.com/annotation/5cc20eb9965c1b001b5c828d

      _center_shadow


      This image is licenced under Creative Commons licence and can be used/modified freely in any possible way

      Create your own annotation at https://www.windy.com/annotate

      posted in General Discussion
      Štěpán Šubík
      Štěpán Šubík