Heat builds in the UK this week…but risk of a twist at the end!

June 1, 2013 — Leave a comment

Temperatures through this week look increasingly summery with dry weather courtesy of our summer friend the “Azores High”.  Coincidentally, the meteorological summer starts today, June 1st.  Temperatures are due to mostly increase this week in Reigate possibly topping out at 25°C by next Saturday but the building heat comes with a twist!  The HIGH pressure we are enjoying over the UK right now is due to slip North and then West. UPDATE: this will take its time… breakdown looks like Mon/Tues next week, weekend fine!
later next week

This will expose us increasingly to LOW pressure over Europe and a feed of warm air from a LOW in Biscay.  Summer heat combined with LOW pressure can yield thunderstorms as thermals lift into the atmosphere creating big cumulonimbus clouds.  A feed of warm air (warm air advection) will also encourage this thundery activity.  

early june rainfall europeThe continental LOW over Europe has been a breeding ground for thunderstorms and heavy rain which has plagued the continent recently.  With high pressure possibly leaking away from the SE UK by next weekend, models are suggesting that, with a stronger sun and lower pressure, heavy thundery rain could invade from the LOW pressure to the South.  So, enjoy our summer friend this week, the Azores HIGH, because it could break down and allow convective storms and fronts to move across the UK from the continent by next weekend.  

Increasing storm risk

Increasing storm risk

The above graphs show rainfall and CAPE.  CAPE is a measure of convective available potential energy and is a predictor of showery and thundery activity. CAPES so far this year around Reigate have been max of around 300 j/kg: giving a few thundery showery days during May.  Some model runs predict CAPES of 800j/kg later in June which could yield some bigger thunderstorms.  Nevertheless, recent tornadic supercells in Oklahoma have readily built CAPES in excess of 6000 j/kg so ours are small-fry by comparison.  Also, this is along way off and models do get things spectacularly wrong, so storms are certainly not a certainty but worth considering as an idea. 

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