BBC monthly outlook
Summary
A changeable end to March. Drier, settled in April
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Wednesday 17 March – Sunday 21 March
Drier for most with a cooler weekend in the South
From Wednesday onwards this week the weather will turn drier for most with some sunshine as high pressure builds. However, eastern areas may be clipped by some patchy rain or drizzle moving southwest through the North Sea, especially on Thursday. These winds will bring in some colder air from Scandinavia too, but only in the south-east of the UK. High pressure will remain in place throughout the rest of the working week and the weekend, keeping things mostly dry but with plenty of cloud around at times.
A north-south temperature contrast is likely to develop into the weekend, with the south and south-east of England seeing below average temperatures while the rest of the country is near or a bit above average. Clearer skies and calm winds in the south will lead to some widespread frost overnight on the weekend mornings. Meanwhile, cloudier skies and a warmer air mass in Scotland will keep things above freezing, leading to a peculiar situation where London is likely to freeze while Glasgow stays well above zero!
There is potential for a weak weather front to push into western areas late on Saturday or perhaps Sunday, bringing some patchy rain. This is dependent on the strength of high pressure overhead, which may well keep this front offshore to the west.
Monday 22 March – Sunday 28 March
Wet at times early in the week then turning drier
For the end of March, an unsettled pattern is expected as high pressure recedes back to the Atlantic. This will allow the main low pressure track to shift back southwards, with weakened weather systems moving across the country from the northwest. In this sort of set-up, most rain would be expected in northern and western regions, while eastern and southern areas see lighter, patchier rain, if any. However, high pressure is likely to return from the middle of the week, bringing drier conditions and milder air from the southwest again. This high will keep moving eastwards in contrast with the high from this week that will be largely stationary, so the dry weather will be shorter-lived.
Temperatures should be near normal averaged through the week but with fluctuations as frontal systems come and go, some temporary chillier northwest winds are possible early on. Confidence is not high on this period of weather because we are seeing some discrepancies in the medium and long-range computer models. Although we expect the weather to be unsettled with some lengthy dry spells, there is a possibility that high pressure will be much more dominant and keep things very dry, cloudy, and a bit colder than normal. This is about a 30% chance.
As is typical every spring, the computer models are really struggling with pressure patterns as we head into April, which is hampering our forecast confidence. This happens because the mid-latitude regions are beginning to warm up from their winter state, and this warmth gives weather systems more energy. The energy boost causes them to be a bit more unpredictable in the long-range.
Monday 29 March – Sunday 11 April
Possibly settling down again later in April
Moving into April, the outlook is very uncertain. While models tell one story, our statistical forecasts (where we examine previous years with similar large-scale weather patterns around the globe) are for another. Looking at the computer models first, they suggest a re-build of high pressure, bringing a return to generally settled weather by the second week of April, with less wind and rain than normal during this part of the springtime. Temperatures would most likely be close to normal during the day, but the nights could be rather chilly in places, and perhaps foggy. The computer models have been consistently forecasting a very dry, high pressure dominated pattern all through March which has so far failed to materialise. There are some encouraging signs that this will eventually develop later in April, so perhaps the adage that a broken clock is still right twice a day has some merit here.
However, models are struggling with the possible position of this high pressure, and there will always be chances of frontal systems brushing past from time to time, so it will not necessarily be completely dry. Scotland and Northern Ireland would be more likely to see rain from these systems, and an alternate scenario indicates weaker high pressure with chances of unsettled weather returning to a wider area. This is about a 35% chance.
Interestingly, another alternate but lower-risk scenario, around a 10% probability, has high pressure shifting farther north with low pressure developing over the near-continent. This would mean chances of rain and even thundery outbreaks in the south rather than in northern and western areas.
Further ahead
We will be able to examine early April for more detail and perhaps pin down the likelihood of a drier middle of spring versus some proverbial April showers.
https://www.bbc.co.uk/weather/outlook