BBC monthly outlook
Summary
Some very warm days mixed with showers, thundery
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Wednesday 13 May – Sunday 17 May
Colder air will head east. Staying dry and sunny.
For the rest of this working week, we will likely see the late-season cold snap from the first half of the week begin to moderate. High pressure will slowly shift nearer to us from the northwest, and by Friday this should cut off the northerly winds and colder airflow. Temperatures should then return to near normal as we head into the weekend.
High pressure is generally controlling the weather for the country this week and weekend and this will tend to keep things dry and mostly sunny. The main exception to this is northern Scotland, including the Western Isles and Northern Isles. Here some weak fronts will be able to creep in from the west and keep things cloudy with occasional patches of rain.
Occasionally, especially Friday night and perhaps again on Sunday, rain will reach as far south as the Central Belt and Northern Ireland. Further south it will stay dry for most, but the odd afternoon shower is possible for parts of the westernmost counties at times.
Confidence is high overall, but a bit lower on the exact temperatures we can expect this weekend. This should generally be near or a bit above average, but it is possible we might cling on to the colder air for a day or two longer.
Monday 18 May – Sunday 24 May
Wetter and breezier in the west
As we head into next week, high pressure will continue to be the dominant weather feature for the UK. However, instead of being northwest of the country, it will tend to be to the south and perhaps southeast. This will allow some milder air to feed in from the sub-tropical Atlantic, and temperatures are likely to trend well above average. This will be felt most in the southern half of the country, as Scotland and Northern Ireland will tend to be cloudier more frequently from nearby weak fronts. It will be drier though with rain struggling to even get to northern Scotland.
As the high shifts to the southeast, there will be a chance that we might get some short-lived pulses of southerly winds that will bring some very warm but thundery days. This will be more likely later in the week.
Confidence is generally high this week, but as before, the exact temperatures are still a bit elusive. It is highly likely we will be above average, but by how much is less certain. There are not signals for any prolonged cold outbreaks like we saw early this week.
Monday 25 May – Sunday 7 June
Generally warm but occasionally showery
For the rest of May and first week of June, high pressure will continue to be the main weather feature. The high will often be to the southeast of us, so like before we expect some warm air to feed in from the southwest and keep temperatures above average with some sunny, calm days.
Heading into June there are stronger signals today that high pressure will tend to shift to the east. This is more favourable for some plumes of very warm air to come in from the south. These plumes tend to be humid, very warm or hot, and bring some widespread heavy showers or thunderstorms. These will be most likely in the southern half of the country but can reach everyone eventually.
However, the major caveat to this forecast is that these plumes can be very fickle, and if they miss the UK by staying in France or the Low Countries the weather story will be very different. In general, it will likely be a warm start to meteorological summer with plenty of dry, sunny days. A few humid, very warm and thundery days will likely be mixed in here and there as well.
Further ahead
Just how warm will we get in late May and early June and how much should we expect some late-spring/early-summer heat and thunder?
https://www.bbc.co.uk/weather/outlook