BBC monthly outlook
Summary
Mostly dry and settled, uncertain temperatures.
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Saturday 17 April – Sunday 25 April
Dry and settled for most, slightly cool.
High pressure that has been overhead throughout the past week will begin to weaken and shift away to the east this weekend. This will allow temperatures to moderate. This will also let a weakened cold front into western and northern areas, bringing some patchy but mostly light rain.
Southern and eastern areas, and most of England, will tend to have mostly sunny and dry weather this weekend, although the sun may be hazy at times. Early next week as high pressure finally slides off to the east, the weak front will pass through southern and eastern areas too. However, by this point the front should be so weak that there will be hardly any rain on it at all.
What happens next, from Wednesday, is where things get a little bit tricky. A second high pressure system is expected to build in from the Atlantic, bringing more dry and settled weather to the UK for the rest of the week and following weekend. However, the temperatures are still pretty tricky to pin down, even at this relatively short range. This high is likely to grab some air from near Iceland and the North Atlantic. Therefore, temperatures are likely to dip below average for at least a few days.
How far east the high pressure shifts will determine how cold it gets into the weekend. Right now, the latest computer model guidance is suggesting a third Arctic blast with temperatures falling well below average again. However, there is stronger support for things to be cool, but not overly cold. The computer models are likely overestimating the magnitude of cold by developing a brisk northerly wind. Confidence for next week is medium overall, with low confidence on the temperatures but high confidence on dry, settled weather.
Monday 26 April – Sunday 2 May
Likely dry and settled with cool Atlantic air.
For the end of April and start of May, the temperature forecast doesn't get any easier to pin down. High pressure is expected to be a major player in the weather pattern for northern Europe. But we are having trouble working out exactly where it will end up. There are strong signals for high pressure to be nearby in both the computer models and our historical analogues (where we examine previous years with similar large-scale weather patterns around the globe to what we are seeing now).
We are leaning a bit more on the historical analogues given the recent very poor performance from the computer models. These analogues suggest nearby high pressure, so we have reasonably high confidence in a settled and largely dry pattern. The temperatures will be extremely sensitive to where the high is and what sort of air the winds will blow into the UK.
If the high is mainly to our west, we will get colder Atlantic air from near Iceland, so temperatures will tend to be below average. This is the outlook we prefer, which has some support for computer models too. If the high is too close to Iceland to our northwest, we will get Arctic air and temperatures will be well below average.
If instead the high shifts east and over Scandinavia, we can tap into Spain or Mediterranean air and temperatures will climb above average. This pattern would also be a bit wetter for southern areas with some heavy rain showers from France. These temperature shifts can happen if the high centre moves by as little as 500 miles, which might seem like a long way for us, but it's a very short distance for a continent-sized weather system! Confidence for temperatures remains very low.
Monday 3 May – Sunday 16 May
Settled for a time, perhaps more unsettled later.
The first half of May should bring further high pressure for a time, leading to some drier weather with changeable temperatures as the high centre shifts about. This is again supported by some of the computer model outlook and a many of our historical analogues. Similar to the previous weeks though, we can't pin down where exactly the high centre will be. The temperature forecast is extremely sensitive to the location being precise.
What we can tell you with some reasonable confidence is that May should start out largely dry and settled with perhaps a bit brief spells of rain for some.
As we head towards the middle of the month, high pressure may shift away for a time and allow the storm track to strengthen and return to northwest Europe. This would bring more unsettled weather back to the UK after a lengthy dry spell along with milder temperatures as warm fronts drag in sub-tropical Atlantic air. This pattern is more likely to develop later in May, and we will have to wait for the large high pressure in northern Europe to ease first. Overall, confidence is low for this range.
Spring is traditionally a difficult period for weather forecasts to capture the long-range patterns, and this year is proving to be no exception to that rule.
The risk scenario is that high pressure remains strong nearby, keeping things settled and making for a largely dry month of May, after a very dry April for England at least.
Further ahead
We will have some fresh data to re-examine our forecast through mid-May and hopefully will be able to shed more light on the temperatures we can expect.
https://www.bbc.co.uk/weather/outlook