#Reigate: a cold flirt with winter looks possible for SE but it’s not the end of the Weald… :-)

November 28, 2013 — Leave a comment

Latest update Saturday 30/11: confidence really building for this event: cold shot end of week Fri 6- Sat 7 / Sun 8 Dec but not lasting long.  Could be some threat of snow / wintry ppt for SE but most likely just rain/sleet but with a cold wind.  More details later but end of next week CHILLY! An additional feature on ECM model is a wave depression on the northerlies running down the north sea arctic winds: could introduce snow to North Sea coasts esp Netherlands/Germany but also potentially E / SE UK. The episode will be short-lived though. stay tuned!

While this weekend will be cool and dry, things might possibly be hotting up for a more significant cool-snap end of next week and into next weekend (7-8Dec). Some models show an attempt at an early December cold snap possibly developing later next week Thurs/Fri 6 Dec and over the weekend with a cold Arctic flow across the whole of the UK and reaching the Weald / SE.  (when) If this comes off, the Arctic flow will be brought to us by a LOW moving over Scandinavia and a HIGH nuzzling in from the Atlantic. The two closing up will squeeze the pressure gradient urged on by an active jetstream plunging in from Greenland which will increase the northerlies to make things feel chilly, especially on the coast and anywhere exposed to the wind. So… it could be a proper cold snap if models come into agreement: currently they are not really coming into line and, while the ECMWF looks dramatic (see chart below), the GFS is keeping the cold further north only skirting Scotland with snow while the South stays in a relatively milder flow: so one to keep in mind but it’s not certain, yet! Latest ECM run still showing significant chilly plunge from late next week/next weekend … but high topples in quickly (see ebelow)

28-11-2013 22-06-16

29-11-2013 07-39-08

If it does happen, typically an Arctic airmass brings snow to Scotland, snow showers and cold and blustery conditions down the North Sea but probably just bright breezy and cold conditions to Reigate. Occasional wintry showers cannot be ruled out for us, though.  At this stage it really does look like a brief episode with a HIGH building over the UK the following week (by 11 Dec) but a cool frosty theme is likely to continue under clearer skies as a high builds in encouraging a cool northerly regime to persist.  This is all worth keeping an eye on but the set-up is not primed yet for a sustained wintry blast because:

  • the Atlantic block isn’t strong enough and a toppling high is likely to spill over the UK shutting the door on any sustained Polar air.
  • the jetstream is predominantly over or even north of S England and this keeps us in westerly or slightly milder conditions.
  • the NAO is weakly positive which means more westerly winds and stormy, milder conditions with HIGH pressure to south and LOW to north.

28-11-2013 22-21-44

Despite these indicators of benign winter weather for the UK, there is a huge mass of extremely COLD air on the threshold of spilling across the UK at any moment.  It is never very far away and, with the jetstream wildly migrating north and south, it is quite likely that some intense cold shots are possible as we push further into December.  All a mixed bag: the HIGH forecast should keep us dry, cool and frosty into mid Dec but expect the odd cold incursion as a distinct possibility.

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