Cold Canadian air pumped up ana-front with gusty winds and heavy rain overnight

December 19, 2013 — Leave a comment

Reigate recorded a max gust of 36 mph last night as a vigorous ana-cold front produced a SQUALL LINE of extra heavy rain and gusty winds that rapidly crossed the country from west to east.  Needless to say, the squall line reduced in strength as it arrived in Reigate and the SE but we still experienced some gusty winds early on.  Nothing like as strong as the 80mph+ winds further west in Wales with associated hail.  An ana-front is where the warm sector air is forced to rise more vigorously than “usual”, in this case due to a strong jetstream encouraging uplift of air from the surface due to divergence and rapidly falling pressure aloft.  This literally “hoovers” air off the ground and produces lots of condensation, thick cumulonimbus clouds and plenty of heavy rain. Wind max during this storm for UK: S Uist 90mph; Plymouth 85mph. Other high winds include:

max gusts assoc with cold front

max gusts assoc with cold front

The culprit was the LOW pressure shown below in the UKMO analysis chart for 18 Dec.  A cause of this extra vigorous cold front was cold Polar air originating from Canada.  Spot the brisk W/NW winds following closely behind the front.

18-12-2013 20-24-36

The front produced 7.6mm of rain in a few hours. In total, since Saturday, Reigate has had 30mm of rain, so expect river levels to be high.  The River Mole has a flood warning in place from the Environment Agency. The Daily Express made a good call and got their prediction spot on a week ago with this article http://www.express.co.uk/news/nature/448402/Freak-storm-to-batter-Britain-100mph-winds-and-downpours-to-cause-chaos

What next?  There’s a calm period with a bright pleasant cool day coming up before more windy weather hits late Fri and heavy rain early this weekend.  A powerful jetstream is making for some stormy weather in the run up to Christmas.  There is the threat of a Channel storm around Christmas Day with possible heavy rain and gales for the south. Or the ECM if bringing in a very intense storm for the NW of the UK on Xmas Eve. Take your pick!

19-12-2013 07-05-43

19-12-2013 06-55-10

More technical details on ana fronts here http://www.zamg.ac.at/docu/Manual/SatManu/main.htm?/docu/Manual/SatManu/CMs/Cf/backgr.htm

and LEWP line echo wave pattern/squall lines http://www.estofex.org/guide/1_4_3.html

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