Awaiting Downward PropagationAdded : Wednesday at 15:25 Right, a nice heavy meteorological discussion to welcome you back to work. You are probably aware that an SSW (Sudden Stratospheric Warming) event is happening across the Arctic. This has been pretty well forecast by most of the global models and you can see the latest chart here :-
High pressure in the upper atmosphere across the Arctic where there is usually the polar vortex in Winter. These things happen, usually towards the end of meteorological winter, but this year we are getting one a little earlier.
When these events happen, usually, a week or two later we tend to see the propagation towards the surface. This is where the lower atmosphere "couples" with the upper atmosphere, high pressure develops over the Arctic and the traditional cyclonic circulation becomes more anticyclonic.
This is akin to stirring a cup of coffee and keeping the bubbles in the centre and then deciding to stir it the other way for a bit (give it a try this afternoon if you are bored).
The problem is, that sometimes the "coupling" doesn't occur. It usually does, but not always. If it does, then the colder air from the Arctic spreads South across mid latitudes. But, and here is the BIG but, the regions where the colder air feeds South vary hugely. Sometimes it's Asia, sometimes it's Central Europe or sometimes it's the mid Atlantic!
Right now, the GFS ► is showing little signs of coupling across Western Europe. Here is the chart for next Wednesday :-
Colder air coming into Central Europe, but even this is transient. A week later and still no signs of height rises to the North :-
So, an SSW event happening which elevates the risk of height rises to the North, but the models showing no signs of "coupling" just yet.
Keep an eye on the GFS ► and ensembles over the next few days though to see whether they pick up on it. Most global models struggle with this "coupling" until the SSW event actually takes place.
At the moment though, there is nothing to get meteorologists too excited across our part of the world with regards to this SSW event.
METEOROLOGIST : MARSH |