Temperatures above average for mid-March as warm plume sweeps through UK

The mercury will rise today before peaking on Wednesday and Thursday at a possible 21C – well above average for mid-March.

Met Office meteorologist Greg Dewhurst said: “On Tuesday morning, although it will be a mild start, it is cloudy with outbreaks of rain and drizzle across western parts, but the cloud should lift and break allowing sunshine to develop, and here is where we see temperatures lift to 13C or 14C.

“On Wednesday, we start to see high pressure building and although it is a grey start, with some mist and fog, the vast majority of us will have a dry day, and particularly in the south temperatures will be well above average reaching close to 20C towards London.

“In the sunshine, UV levels are rising, so if you are out in the sunshine, you may want to put on suncream.”

Warm weather will be driven by a double whammy of soaring high pressure and sultry southerly winds.

Behind the change will be the jet stream, twisting and turning to switch pressure patterns from low to high while steering in from the tropics.

The warm spell will follow a wet and chilly start to the week with more rain and even the risk of snow over the Scottish Highlands.

Mr Dewhurst said: “It is a bit of a chilly start, but it is all change over the next few days as Atlantic weather systems bring some milder air across the UK then high pressure builds and we see temperatures rising much above average for the time of year.”

Netweather’s Ian Simpson added: “The warmth is forecast to peak on Wednesday, when large areas of England and into east Wales will reach the high teens Celsius, and we may see somewhere nudge 20 or 21C, which would make it the warmest day of the year so far.”

While some forecasters think 21C is possible mid-week, others warn easterly winds may sneak in to take the edge off.

Regardless, the warm weather is likely to be short-lived with thermometers dipping ahead of the weekend.

Jim Dale, meteorologist for British Weather Services and co-author of ‘Surviving Extreme Weather’, said: “I think Wednesday will be the best day for the warmth, with temperatures above average for the time of year.

“There is a risk, though, that we might get an easterly, so 19C may be the peak.

“Southern counties will start to feel much more pleasant as we get towards the middle of the week, but ahead of the weekend there are signs of a breakdown.”

Weather models agree on a warm spell during the middle of the week, although subtle differences in the position of high pressure will twiddle the thermostat.

Met Office meteorologist Alex Burkill said: “It is possible that some places towards the southeast could be on the colder side, but another set up has the high just a little bit further south, and that is a slightly warmer direction.

“But, high pressure looks nearby in most of the set ups.”