SSW and the PlungeAdded : Monday at 13:55 By now pretty much every man, woman, dog and cow knows that a rather impressive SSW or Sudden Stratospheric Warming event is currently taking place above the Arctic. These tend to happen during February and March as we head out of meteorological Winter and into Spring.
What tends to happen in scenarios like this is that the people who know little about it tend to get the most excited.
Here is the vortex now :-
You can see how the vortex has been displaced over parts of Northern Canada and instead we have high pressure and warmer temperatures across the Arctic circle.
When this happens, it has the effect of allowing the colder Arctic air which has been kept in check by the low pressure systems to filter South. Because in the Northern hemisphere we have land masses in the form of Canada, North America and the Eurasian plateau this means that the colder air manages to make it a further South and affect more places than a similar event in the Southern Hemisphere would.
The effect of this usually starts to appear a week or two after the actual SSW event as it propagates down towards lower levels in the atmosphere.
Numerical models are pretty darn good at picking up on the effects and developing blocking patterns from this event, but as to where or when the colder air heads South is still wide open to debate.
The GFS ► has this chart for the end of February :-
You can see high pressure to the East of the UK, but now take a look at where the colder air is :-
Ta-da! Miles to the East of us. Sure, an SSW event takes place and sure enough we have cold air head South as the propagation takes place, but the UK sits in a mild Southerly flow whilst the colder air heads South across parts of Eastern Europe towards the Aegean peninsular.
Another lobe of colder air heads South across parts of Eastern Russia towards Korea :-
So, SSW events tend to lead to colder air from the Arctic heading South a week or so after the event occurs. But where the colder air heads South is pot luck and sometimes it's Western Europe, sometimes it's Eastern Europe and sometimes it's the middle of Russia.
It's why meteorologists don't get too excited about these things until models resolve where the cold air outbreaks will occur... and we, you, those dogs and cows will have to wait a few more days to find out.
METEOROLOGIST : NOTTHATEXCITED |