BBC monthly outlook
Summary
Settled but cooler this week, then changeable.
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Wednesday 10 April—Sunday 14 April
A cooler, settled week. Cloudy at times
A weak frontal boundary will linger briefly Wednesday morning across the far south of England, keeping things a bit cloudy down there, but high pressure building in from the north will push it off into the Channel, leaving the UK dry and settled for the rest of the week. However, as a ridge of high pressure builds in, winds will shift easterly to north-easterly and bring in some noticeably cooler Scandinavian air, bringing temperatures down to a few degrees below average for the second half of the week.
High pressure will remain in charge for the rest of the week, keeping things settled. The north-easterly flow will be mostly dry, but will likely bring in quite a bit of cloud from the North Sea at times. Nights will be marked by chilly fog and some frost in a few clearer spots, while the afternoons will be partly to mostly cloudy, with the best of the sun in western and central areas. Occasionally some isolated pockets of drizzle will drift in with some of the thicker cloud banks from the North Sea, and in eastern areas the cloud may linger for most of the day, keeping things dreary and chilly.
As we move into the weekend, an upper level low will drift across Central Europe, which will bring the a slight chance of the odd shower into the Southeast from Saturday. This will also increase the winds in the South, so the weekend will be a bit breezier than the week. The low may also bring in a thicker band of low cloud across the North Sea into the Southeast coast, blanketing East Anglia and possibly reaching into London Sunday, making for a grey finish to the weekend. Further north things will stay settled and dry, with the greatest risk for North Sea low cloud in the Southeast.
Monday 15 April—Sunday 21 April
Turning more unsettled, but also milder
Early in the working week high pressure to the north will likely have weakened enough to allow a return of more unsettled weather into the UK, and much of western Europe at large. This will also bring in some milder air from the southwest. High pressure will be lurking somewhere across Europe this week, and this is the main source of uncertainty. Models are struggling with just where this high pressure might be, and as a result the forecast for the UK has been changing significantly. High pressure located a bit further west will keep most of the unsettled weather over Ireland and Scotland, leaving England and Wales largely fine and dry. A slight shift to the east, and things become wetter and windier for all.
Confidence is still low, but growing for this week overall. We are reasonably certain that there will be a return to a period of unsettled weather mid-week, with an upper level low on Tuesday and Wednesday bringing some showery weather, spreading north on Thursday. Towards the weekend of the 20th and 21st there are indications that we will start to see more widespread high pressure across central and western Europe again, which will start to push low pressure off to the west and bring more settled weather back into the UK. However, the ridge of high pressure is expected to continue heading westwards into the North Atlantic, with a trough of low pressure moving in from the east behind. This may occur on Easter Sunday or perhaps the following Monday, and will bring in a spell of unsettled weather.
Monday 22 April—Sunday 5 May
Warm, settled end of April and start of May.
As the high from earlier in April heads westward into the North Atlantic, a trough of low pressure will replace it from the east. This will bring in a brief spell of unsettled and cooler weather, likely lasting for much of the week starting Monday 22nd. The crucial aspect is what day this unsettled weather will drift in. There is still a lot of uncertainty on the exact timing, so confidence remains low, but the bulk of the Easter weekend is looking to stay settled currently, with the shift to unsettled weather taking place Monday 22nd or Tuesday 23rd .
The wave pattern across Europe and the North Atlantic will continue to track westward, so after several days the low pressure trough will slowly head out into the North Atlantic, with ridging building in behind from the east. This high pressure will bring in much milder air from the south, along with largely settled weather, although the settled weather will likely take a few days to become established. The last full week of April will likely be mostly settled with occasional weak fronts bringing some light rain. By the first week of May, high pressure should be firmly established across the UK, keeping things warm, dry, and settled.
Next Update
While the start of the Easter weekend should be settled, we can hopefully pin down the timing of unsettled weather in the following week.
https://www.bbc.co.uk/weather/outlook