Low-pressure systems have increasingly tended to dominate our weather toward the end of August. Over the past 5 days the wind has shifted more towards the west, displacing the warm and humid conditions that broke down into thundery downpours last week, which brought flash-flooding in places.
Temperatures are now close to average for the time of year, though will creep a little above average later this week in the south, as the jet stream shifts north and winds turn more towards the south.
Jet stream which was south of the UK end of last week is shifting north over the UK this week, meaning wetter weather shifting north too
The current changeable pattern, with low-pressure systems regularly moving in from the Atlantic near or over the UK will continue this week and likely next week. However, with the jet stream shifting north this week and into the weekend, low pressure systems and associated fronts will tend to track further north than over the past weekend.
This means northern and western areas of the UK seeing most rainfall, with 20-40mm widely, though locally much more across the northwest, from regular spells of rain moving in off the Atlantic from Wednesday and through the weekend. Perhaps as much as 60-80mm across north Wales, Cumbria and western Scotland. While southern England and East Anglia will see much less, perhaps some patchy drizzle or light rain Wednesday and Thursday, then a brief rain spell of rain on Friday - as a weakening cold front clear southeast. The weekend mostly dry.
Rainfall through to the end of Sunday - very little for SE UK, very wet in the northwest.
Although it could turn rather wet and windy across the north over the weekend, it could turn very warm or even hot towards SE England and East Anglia - more especially Sunday as winds turn southerly here - with some models showing temperatures reaching 25-27C.
Very warm in the southeast on Sunday?
However, there are signs that the jet stream will shift south again early next week, bringing areas of low pressure off the Atlantic further south, with a greater chance of more useful rainfall for southern areas. Winds may turn northwesterly or northerly for a time too, bringing cooler days and nights.
Wet weather returns to the south next week, as jet stream shifts back south?
There are signs from extended medium range and sub-seasonal model output that high pressure may build in from the Atlantic around mid-month, bringing drier and more settled conditions across many areas and perhaps warmer-than-average temperatures too. High pressure could dominate for a week or perhaps further to the end of the month. But less certainty on a dry and settled spell for the whole of the 2nd half of September.
Signal for high pressure to build from the west from around mid-September
Looking further ahead, we will have an autumn forecast out in the next week. But a hint of what we currently think is that Autumn truly takes over in October, with seasonal weather models predicting a high probability of low-pressure systems bringing heavy rain and possibly wind storms from the Atlantic Ocean towards the UK. As a result, it could be a considerably wet month. But despite the rain, it remains on the mild side.
Low pressure (blue) dominating UK weather in October and November as per ECMWF seasonal forecast
The wet weather in October likely continues in November. A persistent westerly flow will ensure a succession of lows bringing spells of rain along with generally gloomy, changeable weather. Early wintry spells seem unlikely for the time being due to the dominant mild flow off the Atlantic.
Hopefully the wetter signal for October and November will go some way to redress the drought that has developed this summer across parts of England and Wales. The wet autumn could be a consequence of the Super El Niño currently developing, which will likely become the strongest El Niño ever recorded later in autumn and through winter.
However, there is no simple rule that “El Niño automatically means a wet autumn.” - as European weather is also strongly influenced by other factors, such as the North Atlantic jet stream, the sea surface temperatures of the Atlantic Ocean; the polar vortex and also the amount of sea ice around the North Pole. That is why El Niño can cause very different weather in Europe in different years.
But, with a strong El Niño, the jet stream in the subtropics can become stronger - which can be reflected in a strong jet stream over the North Atlantic. Current seasonal forecasts show that the influence of El Niño may become increasingly evident later in the autumn in bringing stormy weather to NW Europe.
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