6 Mar 2015

Weekend spring sunshine: 10 things you need to know

1 – Why is it turning milder?

During the past few weeks, the jet stream has been south of the UK, steering low pressure and cold air our way. However, this weekend the jet stream is going to move just north of the UK, allowing high pressure to have an influence on our weather – especially for England and Wales.

2 – Where will the best of the sunshine be?

On Saturday, the best of the sunshine, albeit with a breeze, will be across much of north east Scotland, England and Wales – except for parts of Cornwall, Cumbria and western coastal counties of Wales, which could be cloudy and drizzly.

On Sunday, the best of the sunshine will switch to Scotland and Northern Ireland, as England and Wales turn cloudy with a little rain.


3 – How warm will it get?

In the best of the sunshine, temperatures are likely to reach 13-16C on Saturday, with a 30 per cent chance of somewhere reaching 17C across eastern parts of England.

Even places that stay cloudy on Saturday will reach 10-13C, just because the south westerly wind is bringing such mild tropical maritime air.

4 – Flood risk for the Scottish Highlands

scotland_wxwarning_MO_wpDespite the general theme on Saturday being one of warmth and sunshine, the Scottish Highlands will see heavy rain and melting snow combine to give a risk of flooding for rivers around the Great Glen – resulting in the Met Office issuing an amber “be prepared” warning for rain.

The Scottish Environment Protection Agency (SEPA) is warning of a medium risk of flooding this weekend in a small area, with a risk of some disruption.

5 – How long will it last?

The burst of spring warmth on Saturday is set to be a short-lived affair, with the weather turning more unsettled through Sunday and Monday. However, there are signs that high pressure will return by the middle of next week, bringing more spring warmth and sunshine.

6 – What’s the highest temperature recorded in the UK in March?

daffodils_forest_g_wpWhile the prospect of a few places reaching 17C may seem remarkable for March, it’s actually quite common and some way off the highest March temperature on record for the UK. This stands at 25.6C and was recorded at Mepal, Cambridgeshire on 29 March 1968.

7 – What is a Foehn effect wind?

Moist air rises over the hills and mountains in the west of the UK and condenses to form clouds which deposit most of the rainfall in these areas.

By the time the air reaches the eastern side of the hills and mountains, it contains less moisture – effectively it’s much drier.

Drier air warms and cools more rapidly with elevation than moist air, so as this drier air moves across eastern areas, it warms and has the potential to give higher temperatures than it did when it was laden with moisture – known as a Foehn effect wind.

Given the topography of the UK, this puts places to the east of any hills and mountains in favour of seeing the highest temperatures.

8 – Why will it be cloudier in the west than the east?

cloudy_burnham_g_wpTropical maritime air isn’t just warm, it’s also very moist. Therefore, western areas get full exposure to its moistness as it arrives off the Atlantic ocean.

However, as it travels over land towards eastern areas, it loses some of its moisture – partly due to the Foehn effect described above and also due to the stronger March sunshine punching some holes in the cloud.

9 – What will the rest of March bring?

high_pressure_MO_wpThe weather computer models are currently suggesting that high pressure will be influencing our weather more than low pressure for the next few weeks. This means that there’ll be a tendency for it to be relatively dry.

The uncertainty lies in how warm it will be. This is because the orientation of the high pressure will determine which way the wind is blowing from and whether it’s going to be warm or cold.

10 – Is it true that it’s going to be warm and sunny at Easter?

Recently, some tabloid newspapers have been saying that this Easter is on course to be sunny and warm.

However, with Easter still being a few weeks away, it is impossible to be sure, given the uncertainty I mentioned above about the orientation of high pressure.

If you capture any nice spring weather pictures this weekend, you can send them to me on Twitter – @liamdutton

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