BBC monthly outlook
Summary
Unsettled end to March. Drier weather in April.
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Saturday 20 March – Sunday 28 March
Turning more unsettled as the week goes on.
As high pressure sits over the UK this weekend, the weather is likely to be settled, but rather cloudy with just occasional sunny spells here and there. Temperatures will tend to run a little above average expect for the Southeast, where some slightly cooler air is expected to linger. A very weak cold front should slowly make its way southwards later on Saturday, clearing south by Sunday morning. This will bring a few patches of drizzle or light rain to some, but mainly serve to keep things cloudy for much of the weekend.
Some clearer skies are likely Sunday night. This could lead to a crisp Monday morning for central and eastern areas. Next week, we expect a gradual pattern shift as high pressure slides away to the east. The storm track will then return with weather fronts spreading in from the west beginning around Tuesday. The unsettled weather will then be with us for the rest of the week. Temperatures will likely be a bit changeable, but there are some good signals for a warm middle of the week for the southern half of the country. This comes as southwest winds bring in some sub-tropical Atlantic air.
From Friday and into next weekend, it will likely turn a bit stormier as low pressure drifts nearer to the country. This will bring some stronger winds and scattered showers with a few pulses of heavier rain. Wintry showers are likely for parts of Scotland too as some colder air from Iceland arrives from the northwest.
Confidence is high for the broad weather pattern next week. Although as is typical with the nature of low pressure systems, the daily specifics may shift around slightly.
Monday 29 March – Sunday 4 April
Wet at times early in the week then turning drier.
For the final few days of March and start of April, including the Easter bank holiday weekend, the unsettled pattern is expected to continue. This is due to high pressure building away to our southwest near the Azores and to the east from Turkey into Russia. As we are sat between these two high pressure systems, lower pressure is expected for the UK and the storm track is likely to remain influential over Northwest Europe. This means it will likely continue to be wet and windy as weather fronts sweep in from the west or northwest.
As such, western and northern areas will bear the brunt of the weather. Southern and eastern areas will run a bit drier, although not completely dry! Temperatures will also continue to be fairly changeable, fluctuating around the seasonal average as fronts come and go. Southwest winds associated with warm fronts will bring some milder days. Cooler northwest winds behind cold fronts will bring colder but drier weather. Confidence again is high on the broad pattern, but medium on the extent of how influential high pressure will be on our weather.
There is a roughly twenty-five percent risk that high pressure to the east is much more amplified, keeping weather fronts off to our west. This pattern would also be warmer as southern winds bring air in from Spain and North Africa. But this pattern is a bit more typical of summertime. So despite the computer models suggesting this, it is more likely to be an alternative scenario.
Monday 5 April – Sunday 18 April
Possibly settling down again later in April.
The first half of April is shaping up to see an ever-increasing influence from the high pressure system building over the Atlantic. There are strong signals in the computer models as well as our statistical analogues (where we look at previous years with similar large-scale weather patterns) for this to develop. In addition, unusually warm sea surface temperatures in the North Atlantic will heavily favour high pressure development there as we head deeper into spring. What this means for the UK's long-range forecast is that, April will become drier and more settled as we head towards the middle of the month.
High pressure will build to the west and eventually start dominating the weather for West Europe. There is some uncertainty on the weekly specifics here as things like temperature and precipitation are highly sensitive to how strong and how near the high is at any given time. However, in general as the high builds closer we will likely have a period of northwest winds bringing cooler air from near Iceland. Later a surface high pressure system will brings in some milder sub-tropical air from the southwest. Confidence is perhaps medium in the large-scale pattern across the North Atlantic and Europe.
However, it will be low on the expected weather for the UK due to the sensitivity to the exact high pressure centre placement. Models are struggling with this and it will likely be difficult to pin down much more than 10 days ahead of time. The main risk scenario is that the high will stay too far to the west to block weather fronts, and the first half of April will remain unsettled. There is roughly a thirty-five percent chance of this pattern developing instead.
Further ahead
A closer examination of the first half of April will be in store, with fresh data to hopefully pin down where high pressure will lurk.
https://www.bbc.co.uk/weather/outlook