Spring heading for another fall…

April 20, 2013 — Leave a comment

Reigate: decently warm and very pleasantly “springy” through to mid-week but then a significant fall in temperature and showers to end April!
Cloudless, blue skies bathed Reigate in sunshine all day today and brought temperatures up to nearly 15ºC: perfect for cricket!  However, the air flow was a  cold easterly which meant that it felt cool in the wind, more like 11ºC, but in the sheltered sunshine it was pleasant. London Marathon Day 2013 will start at a chilly -2ºC and will cloud over later, reach max 13ºC and stay dry with only a slight risk of a light shower later; low humidity perfect for marathon runners.

The big temperature graph shows temperatures at 1500m above the surface (at 850hPa), used by forecasters for predicting temperatures because it is a height which smooths-out the complicating influences of surface diurnal (day/night) temperature changes and surface features like sea, land, cities, hills and vegetation, so making overall temperature trends and changes in air mass easier to spot.  This week it’s easy to spot the cool air mass currently over the region, the warming mid-week temperatures and then a fall-off to next weekend.  Three different airflow directions are responsible for these changes, so here’s some detail…

Mon-Tues-Weds
reigate midweekLOW to the north and HIGH to the south of the UK: this pressure pattern will squeeze breezy westerly winds across the UK as a result of the pressure gradient between the HIGH and LOW pressure. A lively jetstream will be directly overhead of the UK and drag an increasingly mild upper westerly / south-westerly air flow from the Atlantic which will bring the risk of the odd shower on a few weak fronts reaching Reigate now and again early in the week but nothing much.


The HIGH creeps up more from the south over Reigate on Wednesday and this should bring warmer and sunny conditions, possibly up to 17-18ºC in much lighter SW winds: so making for a “warmer” HIGH than the one we are currently experiencing which is dominated by a cool easterly airflow over Reigate.

End of next week and next weekend:

It looks like it’s all downhill after mid-week: temperatures are due to take a plunge with HIGH pressure building in the Atlantic with an upper level trough (LOW) digging down over the UK bringing a cold Polar air mass down to Reigate through into next weekend.  Unsettled April showers, some possibly thundery, may break out at the end of the week and over the weekend as this cool northerly air mass meets the warmer surface air and increases lapse rates and instability, encouraging convection.  Next weekend could well struggle to reach 10ºC daytime max , with some showers during the day and nights turning cold.

This is all early days and things could change, so do keep updated on twitter for Reigate weather @RGSweather.

Where are bluebells flowering NOW? Find out here nature’s calendar

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