Thread by @althecat

Attached is a thread showing the transition of Major Hurricane Sam into the a massive 1400km wide extratropical Cyclone (heading towards Iceland.

Here we see latest forecasts of the impact on Europe - beginning with a PWAT (water/energy) 5 day forecast.

https://twitter.com/althecat/status/1445748831379865615

The main feature we see in this animation is a cold dry air blast coming in from the east and colliding with a high pressure system located initially roughly speaking over the Bay of Biscay. The water concentration over the Med/Italy Alps suggests significant precipitation there.

This forecast shows the very complicated evolution of water transport over this five day period - JetStream 11-18km high winds carrying elevated moisture into Europe from the North Atlantic.

Add these two together and you get the rainfall outcomes which are what Europe needs to be concerned about. The already extremely wet conditions over Italy and the Alps are forecast to continue throughout the forecast window.

Here is the latest ECMWF (Euro model) high resolution model rainfall forecast for most of the effected area. One of the key issues will be the fact that these areas have already had several days of rain. There are very heavy rainfalls forecast in several spots.

The other areas which is clearly in the eye of this storm are Greece and the Balkans. First Greece (this is a 7 day forecast from @NOAA's GFS) the Italy one is just 4 days.)

And here's the balkans, also 7 days.