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Weather news and views from Brian Gaze.
Posted Thur 27th September 09:15
Persistence according to Google is "the continued or prolonged existence of something". When it comes to the UK's weather you ignore that relatively simple concept at your peril. As we head towards another winter it is something I will be keeping in mind.
In February this year a record breaking Sudden Stratospheric Warming (SSW) event took place. During an SSW temperatures in the stratosphere rise quickly and the westerly flow slowdowns or reverses. That leads to an increased risk of high pressure blocking, and cold arctic air being displaced to mid latitude locations such as the UK.
The Beast From The East spell followed the SSW in March. Since then my view is the weather hasn't returned to normal in the the UK. Summer equalled the hottest on record and the tendency for high pressure has continued for much of September. It hasn't always been the case of course, for example last week there was a marked contrast as low pressure systems moved in from the Atlantic and brought stormy periods.
Looking ahead and the signs from the medium range computer models are that high pressure will dominate for much of the next few weeks. The GFS chart below for Sunday 7th October is quite representative of much of the current output, although there are differences in the positioning and orientation of the high pressure cells.
The next few months could of course see the weather returning to business as usual. Anyone who discounts that possibility is in my view either telling porkies or showing a lack of basic knowledge. Having said that I come back to my point about persistence and would argue it is equally daft to discount the chance of the rather unusual weather patterns lasting through the rest of the autumn and into the winter.
Now if the prevailing southwesterly flow continues to be disrupted we could see rather cold conditions developing at times later this autumn as the continental landmass cools. It would also suggest an increased risk of cold outbreaks in the winter. Things get really interesting if low solar activity (always contentious), the possibility of an easterly QBO and a weak to moderate El Nino (possibly increases the chance of cold spells during the second half of the winter) are factored in.
Since the SSW in February weather patterns across the North Atlantic region seem to have been out of kilter. Persistence suggests anomalies could continue through autumn and into winter. If that happens the chance of cold spells could be increased.
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