Model output discussion - into the start of Winter

[Anthony Burden]

Going down to the wire with so much uncertainty,not seen this for a very long time.

hang on to your hats as some major surprises are still on the cards for the white stuff 

good exciting times a head for us cold lovers.

[Snow lover 2020]

10 minutes ago, Catacol said:

Imagine a balloon pinched between your fingers. You end up with 2 smaller balloons. This is what warm air fired up into the polar vortex can do. The warm air acts to significantly reduce the temperature gradient in parts, and if 2 blasts of warm air are fired into the vortex from opposite sides of the globe then this acts to “pinch” the vortex just like the balloon between your fingers. We call this a wave 2 event. 

In situations where this happens the removal of strong westerly influence in sectors where the pinching occurs tends to encourage strong high latitude blocking and cold air spills out. However it is extremely difficult to be sure where the cold will end up. In Feb/March 2018 we hit the big jackpot though it was 2-4 weeks too late really to maximise cold impacts. Equally as the blocks form warm air is forced north....and so a split vortex event like this can produce very warm temperatures for some parts. Therefore it is a scenario laced with various scenarios....but in general the disruption to the vortex caused by the pinching increases cold outbreaks in lower latitudes.

Wave 1 events can also occur - warming on only one side of the vortex. Rather than pinch and split the vortex these events push it off its central axis and this can also promote cold outbreaks to favoured parts. Much depends on where the displaced vortex ends up. If Siberian led warming pushes it over Greenland/Canada it tends to be bad news for us (unless you like rain that is....)

What causes these warming wave attacks on the vortex? That’s a very complex subject. Not time to go into that here - go read up on it. Suffice to say that forecast patterns for the next couple of weeks are suggesting the possibility of a wave 2 attack. This doesn’t mean the vortex will automatically split (often the fingers don’t pinch the balloon hard enough to do more than force it a bit out of shape) but it is a start. Weaken it....hit it again in January and we stand a chance of a SSW inspired vortex split. 50% of Niña wQBO winters produce a SSW event big enough to cause serious grief for the vortex. Fingers crossed.

 

Ok but if an SSW in jan occurs and gives us cold snow weather then this invalidates metoffice, BBC’s winter forecasts? They all going for zonal winter 

[Met4Cast]

Just now, Snow lover 2020 said:

Ok but if an SSW in jan occurs and gives us cold snow weather then this invalidates metoffice, BBC’s winter forecasts? They all going for zonal winter 

Yes - But it's very rare that SSW's can be predicted beyond a 2-3 window, so they can't really be factored into any long-range seasonal forecasts. 

[sheikhy]

Fantastic ecm from start to finish!!!begins with a smothering of snow anywhere across england 3 days from now and then cold and frostty after that till the end!!!❄

[Paul]

Locking this now, as it's starting to grind its gears a bit. Fresh one here: