Best posts made by Yves70

@korina
Very nice summary Korina. Will be useful for a lot of users !

@koukgr
As explained by @idefix37, there is no way for Windy to draw fronts. There are websites where fronts are drawn tha you can use.
Having said that, there are alternatives to visualise fronts that you can use with Windy. One way is to use the humidity map at 700 hPa. A front is materialised at this altitude with a humidity above 90%. Another way, combined with the humidity map is the temperature map at 850hPa. Ideally we should use the potential temperature (thêta’w) but still it can give you an idea of the temperatures differences between air massa so in fact discontinuity which is the sign of a front.
Again, those 2 maps don’t replace fronts map but it works quite well

@hgk209
First of all, we should get the confirmation about the exact meaning of the shades of grey. Is it humidity level or cloud cover ? High level of humidity doesn’t necessary mean clouds

@Korina
@ivo
Could you let us know ? Thanks

@nwindy
Yes, the way the ensemble model calculates the probability is as you explain : for instance for the rain, each dot of the 21 dots can give a different level of rain (1mm, 4mm, 10mm,...). Based on that set of different levels of rain, the model can calculate several probabilistic values such as the average, variance,... This will allow you to quantify the risk of rain

Now, if the model has to adopt the same approach for many other parameters, such as pressure, temperature,... And for each parameter do the 21 calculations (do not forget that each calculation is the equivalent of a single deterministic calculation), computional limitation will be the issue if the model keeps the same grid. To overcome this problem, grid is bigger, calculation of the 21 dots for the different parameters becomes ok but accuracy will decrease.

Computational calculation is key. In average, weather forecast improves by one day every 10 years thanks to the computer (super calculator) progress

@captainjack63
Fortunately for the meteorologists working for NOAA or other national institutes, their work and analysis cannot be always replaced by an application or a computer as it is the case for the front map for instance.
Having said that, there are couple of things you can do with Windy to try to see front, and air mass with different temperatures :

1. check the humidity above 90% (very critical) and at 700hPa and 600hPa. You should see the fronts as illustrated :

The red zone shows the front, with humidity above 90% and just after, you can see a huge drop of the humidity with the brown zone

2. check the temperature at 850hPa to follow air mass temperatures. Ideally, you should use the potential temperature (a temperature among others which doesn’t vary with the altitude) but this temperature is not available with Windy. Nevertheless, temperatures at 850hPa will allow you to compare different air mass and follow them, especially on the sea because hills and mountains could otherwise interfere at this level.

Same picture as above, same moment. You can see the temperature differences, as there is an air mass at 0°C followed by an air mass at 4°C. This confirms the front identified above with the humidity map and on top, you see that it is a warm front
This type of analysis will not replace a front map draws by professionals but at least you can get something thanks to Windy

The temperature of the Mediterranean sea is quite high this year. In some ares, temperature at the surface is around 28°C. This is of course due to the hot spring and summer.

This situation is not without consequences :

1. a medicane was formed close to the Libyan coasts and hit last Friday Greece creating a lot of damages because of the wind and rain

2. yesterday, in the South of France, because (but not only !) of the intrusion of very warm and humid air from the sea, combined of course with other factors (instability, anomaly in altitude, wind shear), it created a multi cellular thunderstorm which was stationary : each new convective cell (this is why it is a multicellular system) is created in the exact opposite way of the move of the system in altitude because of the wind shear. This creates therefore a stationary thunderstorm which is terrible in terms of rain accumulation because you can get huge quantities of water at the same place during 24h or even more.
   This thunderstorm created floating and a lot of damages in France (more than 600mm of rain in 24h)

Unfortunately, other episodes like the ones mentioned above could happen in the coming weeks,...

@Joerg78
The model from ECMWF is called IFS. This model has 4 run per day: 0z, 6z, 12z and 18z. So far, Windy gave us access to only 2 run, 0z and 12z (the main run). Now, the Premium users have access to the other 2 run, 6z and 18z

@ginop
First of all, please start to check the posts published on this forum and discussing rainfall forecast.
Example : https://community.windy.com/topic/13586/about-rain-calculate/2?_=1602329137551
There are many others, use the advanced search tool to fine them and to read them. You will find a lot of advices.
Principles are always the same :

1. compare the different models to verify the consistency within the forecast from the different models. It is a kind of statistic approach to give you a level of confidence
2. don’t look only the meteogram which is focus on one location. You should check with the Windy rain map, the rain forecast in an area of let’s say 20km around the location. Often, models foresees no rain at the location but for instance 5mm at only 10km from the location. Thereofore risk is high to get rain at the location.
   Combining 1) and 2) should tell you the probability of getting rain or not

@lbazlen
To complete what @idefix37 said, with the infrared, the colder the tp the higher the cloud is so potentially it could be a cumulonimbus type of cloud associated with thunderstorms but cirrus is also high and cold cloud and not associated at all with thunderstorms. As always in meteo, before taking a conclusion you should check other paramters, for instance check the visible channel as well to see if the cloud is thick or not. If not, what you are seeing with the infrared is probably a cirrus

@Hubert406
Il est important de comparer les différents modèles : ICON, IFS (ECMWF), GFS,... C'est à cela que sert notamment l'outil de comparaison disponible avec le météogramme. Vous pouvez comparer les précipitations prévues par chaque modèle et vous forger une opinion sur la quantité de pluie probable.

Une autre chose à faire est de ne pas regarder uniquement le météogramme qui est focalisé juste sur votre localisation. Il faut regarder la carte des précipitations pour voir si autour de votre localisation, par exemple dans un rayon de 15km, il n'y a pas de la pluie prévue par les modèles. Si 5mm de pluie sont prévus à 5 ou 10km et rien chez vous, il faut se poser des questions quant à la probabilité que vous ayez tout de même de la pluie chez vous, le risque est grand car il suffit d’une petite déviation et vous avez les 5mm pluie aussi

@anthony10
Yes, upgrade is in place and this is the version available with Windy

@CR
No, in general with Windy, you cannot combine different maps, except pressure, geopotential, temperature and isotherm that can be display on any other maps.

One of the typical feature of a medicane is the hot core which is much warmer than outside. It is very interesting and instructive to follow it at different levels. At the beginning, you could notice the difference at low levels, 850 hPa for instance but day after day, you can see the differences, in the core and outside, also at much higher levels. This is because in the development process of an hurricane, the system releases latent heat, among others because of the condensation of warm and humid air at higher and higher level. Here you can see it clearly on the follwing map at 600hPa : +2°C in the core, -2 or -3°C outside. Huge difference !

Very instructive to follow the development of this medicane

@disaster999
I would like to add 2 comments :

1. as @idefix37 and I already highlighted couple of times, Windy doesn’t make any weather forecast model, Windy doesn’t do any calculations with the models, Windy only publishes the data coming from several models and present those data in a very nice and useful interface. Therefore, Windy has no responsibility regarding the accuracy of the data. Only the institutes making the models have this responsibility. Having said that, it is also the responsibility of the user to study the different models and determine which one is the most appropriated for the location and for what he or she is expectating as accuracy. It is also key not to mix the concept of a FORECAST and CURRENT weather. Do not look at models to check the CURRENT weather but check then weather stations or satellite images.
2. In general, severe and local phenomena are still difficult to be modelized by the current models. It is the case for instance for thunderstorms. The reason behind this issue has a name : convection. Convection unfortunately do break one fundamental assumption used by all models : hydrostatism. At synoptic level, atmosphere is stable and this is what hydrostatism is telling. Convection, locally, creates an air circulation starting from the bottom, from the ground or from the see, to the altitude. Therefore, atmosphere is not stable anymore and we are locally in a non hydrostatism assumption which is not yet well modelized by the models even if they did a lot of improvement, especially Arome. While it is easy to predict that a region will have all ingredients to get potentially a thunderstorm, it is very complicated for all models to be accurate enough to tell you the exact localisation of the thunderstorm, the exact timing and the exact intensity (wind speed, rainfall, hail,...). More severe phenomena, as hurricanes, have the same issue for more or less the same type of reason.

@petra-pik
@Korina

I have seen a change in the satellite views : it seems that infra view has been replaced by blue channel view. I guess it is still infra but with another treatment.

Could you please comment on this change ?

Thanks !

@psweetapple
As a Premium user you can get 1h forecast (you have to activate It in the meteogram) and soon 4 updates a day with ECMWF Model in place of 2 (already available on the desktop)

@银祚圣宣圣皇帝
All details and documentation about GFS model are here : https://www.emc.ncep.noaa.gov/emc/pages/numerical_forecast_systems/gfs.php

@joelanier
Windy collects data from weather provider. They don’t do any calculation. They put in one place all data from IFS, GFS, etc... If there is somewhere an institute which can provide for free global front maps coming from their calculation, Windy could think to integrate potentially this map in their app,...

So far, front maps are available from a lot of weather national institutes, like IRM, MET, DWD, Meteo France,... They prepare them manually and then they propose an forecast of this map using models like DWD using ICON to forecast the front map evolution. Issue : starting point is done manually and it is a local front map, not global front map

@claramonti
Your question is more related to climatology than weather forecast

The large scale atmospheric circulation in our latitudes is characterized by fluctuating jet streams between different
quasi-stationary states, called weather regimes. The best known one is the famous zonal regime : this regime brings extratropical cyclones (depressions) over Europe and is especially responsible of storms during the winter.

During the last months, we observed a blocking regim with anticyclonic conditions in the North, forcing the cyclones coming from the West to go down and pass by the South of Europe generating a lot of regular rain like in the South of France. On the contrary, we observed a very dry situation in the North of France and Belgium with almost no rain during several months in a row, which was unusual.

On top, there were also several situations called cut-off or « goutte froide » on Spain, Portugal and Atlantic sea generating a stong warm and humid wind coming form the South. This warm and humid air advection, covered by cold air in altitude, created convection and therefore huge thunderstorms in the South of France.
The position of the jet-stream and his strength is playing a role in this situation

@soukhul
You can use the following scale to convert dBZ to mm/hour :