Sub-Tropical Jet Stream Soaks UK, Models Struggling With Strong Strat Warming…

Written by on December 22, 2014 in Rest of Europe, United Kingdom & Ireland, Winter 2014/15 with 0 Comments

It’s been a very wet weekend and start to Christmas week over the UK thanks to a stuck pattern with connection to the tropics.

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The reason for such persistent, heavy rains is simple, we’ve a major split in the jet coming off North America. The N branch lifts north and the southern branch drops all the way down to Bermuda. The jet reconnects over the NE Atlantic before reaching Ireland and Scotland and because the jet extends south into the tropics, we’re tapping warmer, more moisture rich air than usual. The stuck nature of this pattern means the boundary responsible for all this ‘hose-like’ rainfall doesn’t move and so it rains constant until there’s movement and we’re now finally seeing that with clearing skies, cooler temps.

This global jet stream view shows that split in the jet over E North America and reconnection west of Ireland.

Credit: AccuWeather Pro

Credit: AccuWeather Pro

A strong jet roars over Scotland driving persistent rain into western upslopes.

Credit: AccuWeather Pro

Credit: AccuWeather Pro

Check out these impressive rainfall totals over western Scotland from the last 24 hours. Glenmoriston in the West Highlands received nearly 3 inches of rain within 12 hours yesterday. Some spots over the last 37 hours may have picked up close to 5 inches.

This is similar to the massive rains we saw last month in the same region and also similar but not as extreme as the deluge we saw back in Nov 09 in Cumbria.

Credit: MetDesk

Credit: MetDesk

While it’s abnormally mild and rather soggy, big changes are afoot. Said that before right?

Models remain fixed on a turn to much colder for Christmas and thereafter.

Credit: AccuWeather Pro

Credit: AccuWeather Pro

As you can see, the ECMWF sends the jet south with cold NW winds back in play. Snow showers for high ground following a frosty start and day which only warms to between 3-8C UK wide. Looking cold too for the Low Countries, Germany and Denmark.

Credit: AccuWeather Pro

Credit: AccuWeather Pro

We’ve an interesting storm system on the charts for next weekend. As well as being a significant wind maker, this could draw on enough cold air from Scandinavia to bring the first low level snowfall to the UK. Far too far out to make a forecast but it’s certainly catching my attention.

Both GFS and ECMWF take a deep low SSE over the UK with a large circulation which draws on cold air over Scandinavia. Will look at this is more detail in tomorrow’s video.

ECMWF

Credit: AccuWeather Pro

Credit: AccuWeather Pro

Credit: AccuWeather Pro

Credit: AccuWeather Pro

GFS

Credit: AccuWeather Pro

Credit: AccuWeather Pro

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It seems like we’ve waited a lifetime on this strat warming triggering a true SSWE but latest models show that something’s happening.

Many a great cold wave or winter overall has started mild and wet then transitioned into a stormier turn from rain to snow BEFORE the real deal hits. Could next weekend but that stormy transition?

The GFS, ECMWF and other major models have shown northern blocking and waivering between semi cold and major cold. The truth is, it’s all theory until it actually happens but the below model runs may finally be showing the straw which breaks the camels back. There’s simply too much warming putting pressure on an increasingly weak vortex. The warming in pushing the vortex off the pole and something’s got to give eventually..

As stated back on Nov 1, I believe the end of December/start of January should see winter really kick off. History tells us that SSWE’s don’t devlope until winter, not so much late autumn. December started chilly then warmed up thanks to a +AO/NAO but that’s changing now that the atmosphere is entering a winter state and we’re starting to see feedback of the Nino, SST’s, east QBO and low solar etc.

ECMWF ensemble (51 members)

Credit: Michael Ventrice

Credit: Michael Ventrice

GFS operational

Credit: Michael Ventrice

Credit: Michael Ventrice

My internet connection has been poor this morning and so the video may be poor quality. If your experiencing a jumpy video, apologies.

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