Enjoy the warmth while it lasts because we’re about to return to a March-like chill as we head towards the weekend. The NAO has now ‘peaked’ and is now heading back towards a negative signal, promising a chilly first half to May for the UK, Ireland and western Europe while ridging will bring a nice warm-up over the eastern half of the continent.

An area of rain spreads across Ireland, Northern Ireland and Scotland tonight and will sink south along with the frontal boundary tomorrow into Friday. That boundary splits two very different air masses over the UK and Ireland, holding 9-10C air over Scotland, Northern Ireland and Northern England from the 16-21C air across the South of Ireland and England.

Here’s the GFS 850 temps for Thursday and note the 0C temperatures at 5,000ft covering NI and Scotland.

Here’s that rain tonight according to the GFS.

This promises to bring a thoroughly wet night across much of the Republic, southern Scotland and northern England but appears to weaken as it sinks south tomorrow.

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While much cooler air begins to sink south, squeezing the warmth, a strong southwest wind should help raise temperatures back into the low 20s over Southeast England but it may be tough to reach 10C in many parts to the north of this front tomorrow.

By Friday, the front will have reached the south coast of Britain and will also be south of Ireland, so highs in the 16-20C range will be more like 9-12C Friday with winds turned from SW to NW with snow falling over some hills.

Cold High Builds In For The Weekend

This weekend, although cold and below normal with highs in the 8-12C range UK and Ireland-wide, high pressure will build down from the north, providing decent spells of sunshine but be aware, a decent frost will return for many, particularly away from towns and cities. Friday night into Saturday could be a rather cold night for the time of year with -2 or -3C for many, potentially down towards -6 or -7C in the Highlands.

Below is the GFS 850mb temp chart out at 72 hrs or Saturday.

It’s impressive to see the 0C line covering most of France and all the way into northern Spain this late. Notice the -5 line over Scotland!

GFS surface chart for the same period.

While the UK returns to a colder but more settled regime Friday through Saturday, low pressure will bring wind, rain and much cooler than normal conditions right across France, Spain and Portugal with snow likely over the higher mountains.

Europe: Cold, Unsettled Start To New Week For West, Heating Up In The East

By Sunday, the UK and Ireland loose the high and low pressure well to the north will swing a cold front down over the UK, bringing back the rain and wind as well as an even colder push of air. as the North Atlantic high builds and the classic negative NAO signal returns.

Here’s the GFS surface chart for 108 hrs or Monday

As you can see from the above pressure chart, there’s a strong 1038mb ridge positioned over the North Atlantic, this is sending the trough back into the NW of Europe and reinforcing the chill is the building ridge over eastern Europe. The low north of the UK will keep things unsettled but high pressure should build down from the north on the backside of the front towards the mid week period which should help settled conditions again but the chill holds firm.

There does’nt appear to be a lot of precip associated with the front on Sunday as the air coming down is from a drier source but winds are likely to be strong later Sunday into Monday out of the NW with snow levels getting rather low. With early next week’s set up, it wouldn’t surprise me if some high level routes have to deal with sleet and snow once again.

Here’s the GFS 850 temps for 108 hrs.

The GFS surface chart for 108 hrs (above) shows more blustery, cold shower activity over the UK and Ireland with a brisk, cold NW wind reinforcing the unusual chill but it’s down across Iberia where conditions look nasty with low pressure bringing a cold wind and rain mix with hill snow likely.

Below is the 144 hr 500mb chart which shows the deep trough over ther UK/Ireland with a strong cut off low spinning to the south over Iberia while a big ridge and heat pump is bringing summer-like warmth from Milan to Moscow.

By Wednesday, 156 hrs, the GFS holds the cold trough over the UK and Ireland with -5C temps at 850 over Scotland. Strong sunshine at this time of year should keep temperatures comfortable but under cloud and especially in the wind, it will feel more like March rather than the closing days of April.

GFS 850s at 156 hrs (Wednesday)

Given the return to a negative NAO, the trough favours a western Europe position while a ridge continues the warm regime in the East through the next 10 days or so which takes us into the second week of May. However, while very far out, the GFS beyond 300 hrs, towards May 8, shows the retreat of the cold trough with the hint of warmer air returning. Amazingly, from now till then, there appears to be no real warmth in sight and the next time we see even a mere 21C in the UK, could be near to MID-MAY!

[youtube http://www.youtube.com/watch?v=pyqkwYXspBQ]

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Tags: cold april, cold start to may, cold uk, may weather, uk long range forecast