Thread by @althecat

Here we can see Tropical Storm Bill, which looks very cyclonic now, storming north with an outrider running a parallel line to the west over the US seaboard this morning.

Cyclone Bill, soon to become extra-tropical low Bill seems determined to join the #EuropeBigWet.

https://twitter.com/althecat/status/1404863033709666308

What is now TS Bill was previously shown in models storming across to Ireland and removing the Leviathan Storm from the picture over the weekend. But that didn't happen and the Leviathan storm over the Black Sea is now heading south.

Nothing went quite like the models had predicted.

In the interim we have had a nice break from #EuropeBigWet in Western Europe lately. But it's now due to come to an end. Here in Brittany I currently have rain forecast for the next eight days,

The three forecast animations that follow provide a bit of a map to what comes next. Though we can probably expect the reality to be different, which is far from surprising given what you are about to see.

First up here's a PWAT forecast for the entire North West Hemisphere.

In the above picture yellow is atmosphere with lots of water, red is atmosphere with tropical levels of water which comes from the West African Monsoon. It is currently being recycled in massive quantities after passing through the U.S. which is experiencing endless storms.

The second animation above, also 10 days long shows rainfall accumulating over that period across the hemisphere. The GFS model used here, is not bullish about #desertrain but other models particularly the CMC also shows significant rainfall in the Sahara.

And finally here we see the mid-altitude winds over this 10 day period. What passes at the moment for a jet-stream. But unlike a normal polar jetstream - which keeps cold air trapped in the arctic and mositure out this is, as you can see transporting water all over the place.

Ok so that's the big picture. But back to Cyclone Bill because he is not finished yet. Here is what is currently expected to happen to Bill. He gets to Newfoundland, gets swallowed by a low and then pops out again.

https://twitter.com/althecat/status/1404866052840955904?s=20

And here you see the next chapter in that story. Bill pops back out as an ordinary low. (No longer cyclone Bill, but definitely a related entity). And then Bill 2.0 heads to the UK and stops dead.

Ok then, #EuropeBigWet, what happens next. Short answer - we no longer a clue beyond five days.

Bill not behaving as expected has resulted in 3 model solutions over 12 hours at Day 10 - all wet - which you can see below. The first solution is the newest with Bill over the UK.

Over 10 days all three solutions deliver a markedly different rainfall pattern than previously advised.

So I think we can call this #EuropeBigWet phase 3.

Of course, as we can now see, one small variable, Bill, the storm that could, then couldn't, then did can make things turn out in a completely different configuration.