Heating Up Over Western Europe Once Again But For How Long?

Written by on August 19, 2013 in Rest of Europe, United Kingdom & Ireland with 0 Comments

As the NAO flips positive, so a trough deepens over the North Atlantic while ridging builds either side as a result but pesky unpredictable lows are making the 5-7 day forecast a headache. It’s be cool and unsettled across Western Europe and very cool over the Eastern United States over the past 7 days but warmth returns to both sides of the Atlantic with the classic teleconnection setting up as you can see from the below 500mb chart for the Northern Hemisphere off the ECMWF.

ECH1-96

While heights rise, areas of low pressure forming and riding around the bubbles of warm air are making for a tough forecast. While the Tuesday into Wednesday low that’s been monitored for the best part of a week is fairly easy to forecast, it’s the system that follows that’s causing more difficulty.

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Initially the ECMWF had a slower eastward progression of a low approaching Ireland and the UK towards this weekend and now it’s the GFS with the ECMWF pushing it across Ireland and the UK during Saturday, ultimately breaking the heat.

I have a tendency to sway more towards the current GFS solution of a slower approach due to the ridge and warmth bubble being more influential over UK and Ireland airspace.

Here’s Wednesday with wind and quite heavy rain spreading across Ireland and the Northern half of the UK while an increase in SW winds ‘south’ of the front increases the warmth over Southern Britain. We could see 27C quite easily around London Wednesday afternoon while pouring from Dublin up to Belfast and across the Channel to Glasgow.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

By Thursday that system is cleared out into the North Sea en-route to Scandinavia and bringing showers and outbreaks of rain to Denmark.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Friday looks to see the ridge settle directly over the UK and the western mainland of the continent, promoting 21-24C readings across Scotland and Northern England while Midland and Southern England pushes 28-30C. The Low Countries up into Denmark and southern Norway and Sweden may see 22-26C.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Even Saturday looks good with high pressure strong enough to hold back the low to the west of Ireland. The ECMWF has that low spreading wind and rain across Ireland and the UK. Notice the strong surface high coupled with a substantial upper level ridge which provides large-scale sinking and a lack of clouds. If this chart was to be correct then Saturday would be even warmer than Saturday potentially for the UK but more so the Low Countries up through Denmark and into Scandinavia.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

By Sunday the GFS shows showers beginning to lift north into the UK and Ireland and notice by Sunday it shows a heavier band of rain lifting north.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

By 186 hours or next Tuesday, though unsettled conditions, likely in the form of showers and thundery downpours gains ground over the UK with a trough replacing the ridge (like what the ECMWF has), the ridge and heat appears to dominate western (mainland), central and northern Europe.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Check out the ECMWF for the same period and notice the similarity to the GFS surface chart.

Geopotential3250032hPa32and32Temperature32at3285032hPa_Europe_192

In terms of how long any sort of ‘summer-like’ weather lasts, the GFS ensemble shows the trend towards a negative NAO towards the end of the month and start of September. My hunch is we see a flip in the pattern to what we’ve seen through much of this month, within 10 days.

nao_sprd2

The CFSv2 backs up the turnaround in the upper pattern across the hemisphere at the turn of the new month.

Here’s week 1-2 which shows the ridge core migrating north from Iberia to north of the UK.

wk1_wk2_20130818_z500

By week 3 and 4, ridging gets replaced by low heights and troughiness.

wk3_wk4_20130818_z500

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