Cumulus Support

At the dizzy heights of nearly 100,000 feet, the air is beginning to warm up, which is likely to propagate down through various levels and either split the Polar Vortex, or displace it.

Estimated date is around January 5th. It increases the chances of the UK getting a beast from the east. However, with current synoptics in the Northern hemisphere already favourable for a Winter outbreak, it's quite possible the SSW will scupper those chances.

There's some crazy goings on up there at the moment. Tsetsen-Uul in Mongolia set a new pressure record of 1094.3mb - above there is where the sounding came from that showed the stratosphere warming up.

A storm with a pressure of 920mb may have set a new record for the lowest pressure recorded in the North Pacific too.

Fascinating model watching lately!

Up she goes!

The second image is nearer the top of the stratosphere - winds have already reversed up there, and will filter down through. Those spikes will shot up much further over the coming days!

It'll be interesting to see how major this current warming will be?!

@Mapantz, what’s the latest situation regarding this SSW.

RayProudfoot wrote: ↑Sat 09 Jan 2021 5:06 pm what’s the latest situation regarding this SSW.

I know you didn't ask me, but I can provide an answer.

The SSW occurred early last week and has resulted in a displacement away from the pole of the stratospheric polar vortex. The vortex is not currently split, just displaced. Some recovery of the vortex is anticipated in the short term, but further warming and weakening is expected by next weekend, with the vortex remaining in a weakened state through the rest of the month.

Effects on the troposphere, in which we live and experience our weather, are complex. The polar front jet is likely to be displaced to the south, weakened and have more pronounced meanders than normal. This may lead to more frequent cold air outbreaks in places (not necessarily the UK). Counterbalancing this is the fact that the ENSO cycle in the Pacific ocean is currently in La Nina state. La Nina state typically enhances the north Atlantic polar front jet in the second half of the winter, which often leads to milder and wetter conditions over the UK and western Europe.

So there are two opposing forces influencing the north Atlantic polar front jet for the rest of the winter. Latest theory suggests that the Greenland blocking we have been experiencing for a month (and which initiated the SSW event) will shift eastwards, with more in the way of milder Atlantic air over the UK. The models are indicating this behaviour at long range (> 10 days). The displaced SPV will tend to encourage a more southerly polar front jet - this also shows in the models at long range. So the latest thinking is that the mild conditions will generally prevail across the south, with cold(er) conditions further north. With the south-shifted and weakened polar front jet, cold air outbreaks will still occur and affect the south, so it won't be all mild in these parts. With generally cold conditions in the north and the "battle ground" between cold and warm air across more southern parts, then wintry hazards are anticipated at times.

No sign of a "beast from the east" at present.

Thanks freddie. Very informative as usual.

@Mapantz, @freddie: thanks, interesting!