Turning gradually more settled and warmer
Cold air from near Iceland is expected to linger for the rest of this week under high pressure. As we head into late-April, high pressure will remain in charge, but temperatures will begin to moderate as Atlantic air replaces the Icelandic air. May should see warmer temperatures develop as winds tend to shift more southerly or southeasterly. High pressure will remain in charge throughout and tend to give us plenty of settled and dry conditions with only occasional rainy days.
Mostly dry and cold, but milder this weekend.
In a change from the previous forecast, the colder air that has been with us for most of March and April isn't quite finished yet and is likely to remain for the rest of this week. This is coming with high pressure though, so while it is colder than normal for mid-April, it's also mostly dry and settled too. Afternoons will see cloudsdevelop for many with a slight chance of showers in a few spots, but most of the country will stay dry. Weak fronts nearby will keep Northern Ireland and western and northern Scotland mostly cloudy through Friday.
This weekend, high pressure overhead will begin to shift away into Scandinavia and decline. This will allow the weakened weather fronts from the Atlantic to slowly move into western parts of the UK, bringing cloudier skies, patchy rain, and also moderate the temperatures a little. We still expect temperatures to be below average this week, but it will be only slightly cooler than normal rather than several degrees below normal.
The big question is whether the patchy rain will spread much into England and Wales later in the weekend. A weak ridge of high pressure will extend into Southeast England from the North Sea, and this may be strong enough to keep the rain off to the west and north. Even if the weakened weather front pushes further east, any rain will be very light and patchy, leaving most places dry.
Drier and settled with fresh Atlantic air
The computer models have become better aligned for late-April. They are also in agreement with our historical analogues (where we examine previous years since 1950 with similar large-scale weather patterns to what we are seeing now) so confidence has increased. High pressure is still expected to be in charge across northern Europe at the end of April and this will keep things dry, settled, and not nearly as cold as of late for the UK.
The temperature forecasts are tricky in this pattern and very sensitive to the area of high pressure, but generally we expect temperatures to be close to average for the time of year or perhaps a touch below and more settled weather. Weak weather fronts from the Atlantic may be able to clip northern or western areas at times, so it may not be completely dry and settled everywhere. Eastern and southern areas may not see much in the way of rain apart from the occasional light shower during the afternoons.
Confidence has improved to medium for the forecast with the strongest signals for high pressure to be the dominant weather feature. Confidence is a bit lower with regard to temperatures and there is roughly a 25% chance that it ends up cold again. If high pressure is too far northwest and closer to Iceland, northerly winds will transport Arctic air into the UK for the third time this spring. There is less support for this in the latest computer models, but we still need to keep an eye on it as the cold has been rather tenacious this year.
Slowly turning more settled and warmer
The tail end of April and first part of May will be at the mercy of high pressure that should often be to the north of Europe while low pressure lingers to the south near Spain. The UK will be caught between these two large-scale pressure systems so we are likely to continue to see changeable weather as the weather systems jostle for control.
Again, we see some very poor performance from the computer models, so we are leaning a bit more than usual on our historical guidance. There are some strong signals for high pressure to stick around nearby or overhead, so as we head into May we expect the weather to become increasingly settled, dry, and warm. The low near Spain will tend to send North African and Mediterranean air into France, and this is likely to reach southern areas of the UK too.
One reason for consistency in the statistical models comes from the strong signals in the Pacific and Atlantic Oceans and how that relates to the weather pattern across the northern hemisphere. Some very warm sea-surface temperatures near Japan have helped build a large, strong area of high pressure. Despite this area of high pressure being on the other side of the world, it is helping to create a wavy pattern in the storm track that extends across North America and the Atlantic Ocean. This pattern will promote high pressure in the Atlantic where we have unusually warm waters around the Azores.
So even though there is still low confidence for early May, there are some good signals that high pressure will continue to be a big player in the weather pattern.
Can we expect warmer and settled late-spring weather to develop through May?