BBC monthly outlook
Summary
Unsettled, wet, and changeable for October
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Saturday 18 September to – Sunday 26 September
Unsettled and gradually turning cooler
The start of the week should see some drier and sunnier skies for a time. High pressure will be shifting south across northern Europe and weakening, and by midweek a cold front will begin to push in from the northwest. This first front is likely to bring some rain to the northern half of the country, but by the end of the week and weekend, wet weather is expected widely. Temperatures at the start of the week will be slightly above average and gradually moderate, becoming slightly below average by the weekend.
Monday 27 September to – Sunday 3 October
Low pressure in charge keeping things unsettled
The large-scale weather pattern that develops over Europe next week is likely to stick around for some time, persisting into the middle of October at least. This should see high pressure systems in West Russia and the North Atlantic or Greenland, with low pressure between them near the UK and North Europe. With low pressure nearby or overhead, unsettled weather is likely to be the norm with frequent rain and often breezy days.
Temperatures are a little more tricky to pin down at the moment, and will be sensitive to the exact position of the low pressure system. If the low is east of the UK, northerly winds will make things feel cooler than normal, bringing some crisp autumn days. However, if the low is west or north of the UK, warmer air will feed in from the southwest. Temperatures are likely to shift around day-to-day as the low pressure system nearby moves around.
We may see high pressure build stronger to the west of Europe, extending north toward Iceland, forming a large block for incoming weather systems. If this happens, low pressure will tend to be pushed into Scandinavia, with a consistent northerly wind for the UK. This becomes a colder outlook with temperatures consistently below average with rain less frequent. This scenario, has perhaps a 30% chance of occurring.
Monday 4 October to – Sunday 17 October
Staying unsettled and changeable
Throughout the first half of October, we are seeing some encouraging signals that the large-scale pattern from late-September will continue without significant change. High pressure is likely to be a consistent feature in West Russia, which will be the main driving force for our weather. This high will tend to keep low pressure nearby or overhead and maintain the unsettled weather for the UK and North Europe. Temperatures will be around average but changeable.
Meanwhile, high pressure will continue to loiter to the southwest, occasionally building stronger and sending a brief ridge overhead between fronts. This high will control how many weather fronts we see streaming across the North Atlantic, and the weaker the high is the more weather fronts we will see. Later in mid-October, we may see this high pressure system consistently amplified to the north, increasing the chance of temperatures falling below average and reducing the number of weather fronts passing by.
Our risk scenario for the first half of October is that a strong high pressure builds overhead, pushing low pressure toward Iceland or Norway. This is a drier, warmer, and sunnier outlook which will become more likely if we see a strong Atlantic hurricane push too far north. This becomes less likely as we head further into autumn, but it will remain a risk worth keeping an eye on. There is roughly a 35% chance of this pattern developing.
Further ahead
With low pressure set to be in charge for much of October, we will take a closer look at the chance of some colder weather setting in.
https://www.bbc.co.uk/weather/outlook