Every winter really since 2010 we’ve gone and continue to go through an emotional rollercoaster in the hope of winter here in the UK. Up until now, the polar vortex has been weak and fluid with PV splits positioning favourably for Arctic air delivery into Europe and even the UK. This has in turn slowed the mean trans Atlantic westerly flow between United States and Ireland such that a mean high pressure system has been positioned near Iceland since mid-October, resulting in little Atlantic influence.

 

The unusually weak PV, -AO/-NAO pattern through the second half of autumn has favoured a cold November and open to December across Eurasia extending all the way to the UK.

Last month

This month so far

 

Bye Bye Arctic, Hello Atlantic & Strengthening Polar Vortex?

Much of Northern Britain started Tuesday cold and frosty with a second night below -9C at Aviemore, we’re likely to end the night ahead in double figures as moist SSW winds pick up from west to east.

Could this dramatic midweek flip be a sign of something bigger in the longer term? Hopefully not but the models are indicating a strengthening polar vortex and regrouping near the pole which would favour stronger westerlies and zonal flow into Europe.

The question is, is this ‘possible’ strengthening a trend of simply a reload of cold within the source?

GFS holds mild Atlantic pattern through next 10 days.

Also has a recoupling PV.

But is there too much emphasis on the polar vortex? A neutral AO but -NAO as seem by some models through mid and late month can still mean a cold Western Europe.. Oh I don’t know, let’s just see what the period between now and Dec 15 brings.

Just a week ago, myself and other long range forecasters stated that the polar vortex would remain weak with a potential sudden stratospheric warming event in the coming weeks. Now the models suggest a strengthening polar vortex and with the return of Atlantic westerlies into Europe mid and late this week, this makes me concerned or maybe just confused about the medium and longer term pattern. There are some model solutions bringing the return of a Scandinavian block towards Christmas, suggesting this week’s return to Atlantic is temporary.

GFS meteogram for Glasgow indicates a rise then fall in temperature.

The cold second half to autumn from East Asia to Western Europe I believe can be directly attributed to the remarkable Eurasia snowpack growth during October which, along with record low sea ice brought a strong -AO. However, the QBO remains westerly and this favours more westerly prominence from Atlantic into Europe while an easterly QBO favours an easterly flow.

There’s indication that with the strengthening PV comes a neutral or positive AO but above normal heights over or near Greenland indicates a -NAO. So, there’s a great deal of confliction as for go forward. What will win out?

See this morning’s video.