Out of Africa: at last…heat for the East!

April 10, 2013 — Leave a comment

Update Friday: v unstable atmosphere passing over Reigate Friday after active warm front passes early morning: all ingredients for heavy showers and thunderstorms tomorrow increased risk hail thunder for Reigate, predicted earlier in the week @RGSweather.

Spring warmth is set to arrive big time this weekend, especially from Sunday on wards and particularly in the east of the UK: Reigate could be one of the warmest places so let’s keep our fingers crossed!  The contrast with just a week ago is remarkable with temperatures for Reigate possibly rising to over 20ºC on Sunday and remaining well in the ‘teens during the daytime throughout next week.  There will be a breeze of 15 mph so find a sheltered spot to enjoy the balmy atmosphere or take to the hills with a kite, go sailing, have a BBQ… #getoutside

The initial cause of this long awaited warming is LOW pressure in the Atlantic engaging with a HIGH pressure over Europe which will feed a brisk southerly wind from source regions in North Africa and the Mediterranean.  An upper level ridge building from the south is also critical in feeding warm air aloft (above 5000 m) to the UK.  The jet stream is migrating northwards and helping to feed in this warm upper airmass.  Upper air temperatures at 5000 feet (pic 1 above) are set to rise dramatically from well below freezing last week to +12°C or more through next week: Tropical air has arrived!  The rest of next week looks good with warm and mostly dry weather (but not always) continuing for Reigate and, whilst not always as warm as Sunday, certainly feeling pleasantly springy.  The synoptic configuration is set to remain HIGH pressure in the South and LOW in the North with a warm flow of SW or W winds over Reigate.

However, before all that, Reigate could have some significant rain: while overnight rain should dry up quickly Thursday morning after the front moves North, Friday looks potentially showery and some could be heavy.  April showers are kicked off by heat at the surface causing thermals to rise buoyantly through the atmosphere and condense creating convective clouds called cumulus.  If these grow into shower clouds they are called cumulus congestus or their bigger brother cumulonimbus.  Several of the right conditions for heavy showers are present on Friday such as uplifting air, plenty of humidity and wind shear.  Due to the cold weather thus far, there is currently a lack of heating at the surface to spark off significant thunderstorms but things can change.  Saturday could also have some showers associated with a weak warm front before the much heralded warm and dry weather arrives on Sunday.  Saturday warm front turned out much more perky than first thought… delivered lots of rain all pm! Keep posted on twitter @RGSweather for updates.

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