UK set for temperature rollercoaster as chilly nights follow warm days

ByHelen Willetts

BBC Weather

High pressure lying over the UK means that above average temperatures and spring sunshine will continue for the next few days.

Whilst England and Wales had their temperature peak on Wednesday, Thursday saw the warmest day of the year so far for Scotland and Northern Ireland with the potential for Friday to top that.

But the clear skies that bring the sunshine and warm conditions also mean that overnight temperatures can drop significantly.

Some locations in the Midlands and south of England experienced a day/night temperature difference of around 21C following Wednesday's warmth, waking up to a Thursday morning frost with similar expected for Friday and Saturday.

After Wednesday marked the warmest day of the year so far in many locations in England and Wales, temperatures dipped overnight leaving a frosty morning covering for some.

From Wednesday afternoon into the early hours of Thursday, parts of the Midlands and central southern England experienced a temperature range of around 21C.

South Newington in Oxfordshire reached 19C during the day, then plummeted to -2.4C overnight. Meanwhile, Woburn in Bedfordshire reached 19.4C before tumbling to -1.6C.

These huge swings are known as the diurnal temperature range. Put simply, it's the difference between the highest and lowest temperature of the day.

Afternoons are normally the warmest part of the day because the sun has had time to warm the ground and surrounding air, whilst the coldest time is usually dawn as the ground has lost heat throughout the night.

The UK experiences some of its largest diurnal temperature ranges in early spring due to a combination of factors.

By March and April the sun is much higher in the sky and the days are lengthening, allowing more energy to be delivered and more efficiently. After the long winter, however, the ground and lower atmosphere remain chilly allowing rapid overnight cooling.

Clear skies underneath a spring high pressure systems can increase this contrast further.

At night heat is lost quickly and until the spring equilux, the nights are still longer than the days, all leading to cold mornings.

During the day as the sun rises, those same now sunny skies allow rapid warming as the sun is more directly overhead, leading to warm afternoons.

Dry air heats and cools more quickly than humid air and this can further widen the temperature gap.

These factors combine to increase our diurnal temperature range during the early stages of spring, especially during settled, sunny spells with light winds.

Ultimately solar radiation determines these temperature swings.

The strength and amount of direct sunshine available is always changing with sunnier longer days giving a greater warming potential than cloudy dull ones.

The air, land and sea absorb and release heat at different rates, with land being more reactive than the sea. The upshot is the ranges can often be greater away from the sea.

Hillier areas see greater swings in temperature too. Plus humidity is a big factor as moist cloudy air slows both heating and cooling because water vapour absorbs the heat.

Local geography also plays a part with different surfaces storing heat in different ways, and this can impact both the temperature by day and night.

Due to the temperature swings in March you can only really judge one day at a time.

Check in with BBC Weather online or the app to get the very latest forecast wherever you are and work out if you need to take a big coat or something lighter with you.