20 Feb 2012

A taste of spring this week

After a temporary return to colder weather during the weekend, the mild weather is set to make a return for the week ahead.

In fact some eastern parts of the UK could locally reach 16 or 17C from midweek onwards – especially where the cloud breaks for any length of time, allowing the sunshine to come through.

The source of this week’s very mild weather is a warm flow of air travelling all the way from the Azores. However, despite being a source of warm air, it’s also a source of moist air, so there will be quite a bit of cloud.

It’ll also be windy with outbreaks of rain at times, although most of the rain will fall in northern and western areas, with southern and eastern areas seeing relatively little.

This is not good news for drought prone areas that really need the rainfall given the lack of it over the past 18 months.

So why are eastern areas most likely to see the highest temperatures this week? Well, it’s due to something called the Foehn effect.

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.

Given the topography of the UK, this puts places to the east of any hills and mountains in favour of seeing the highest temperatures – eastern parts of Scotland, England and Wales.

Whilst all places will feel mild, there will be a difference of around 6C between the west and east of the UK.

Western parts of Wales in the breeze, cloud and rain will be around 11C, whereas eastern parts of England will be drier and brighter with temperatures potentially reaching 17C.

At this point, you’re probably thinking how remarkable is this for February? It’s not that unusual and is some way off the February record.

The highest maximum temperature for the UK (and England) in February is 19.7C which was set at Greenwich Observatory, London on the 13th February 1998.

The February maximum temperature records for other countries in the UK are;

Wales – 18.6C at Velindre, Powys on 23rd February 1990

Northern Ireland – 17.8C at Bryansford, County Down on 13th February 1998

Scotland – 17.9C at Aberdeen, Aberdeenshire on 22nd February 1897

If you happen to notice anything spring-like in your surroundings this week with plants blooming or animals becoming more active, then try to catch some pictures if you have a camera to hand.

The easiest way to share them is on Twitter – @liamdutton. I’ll make a gallery of the best pictures on the Channel 4 News website later in the week.

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