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Has the sun set on the first and last day of Spring?!  Spring will return but certainly not for a while.  The rest of this week will be rather wet but mild. An octopus-like LOW sitting out west in the Atlantic will sweep several tentacle-like fronts across the country (count them = 8) and this will bring frequent, mostly light rain to Reigate, heavier rain does threaten on Thursday: check back for details. The big news is the temperature drop between Saturday (+11C) and Sunday (+2C!): this temperature plunge will feel bracing after our all-too brief flirt with Spring and the mild conditions this week. Over the weekend the LOW looks like it will track south of the UK and drag in amazingly chilly air from a BLOCKING HIGH developing over Scandinavia to the NE.  The HIGH will force the LOW to the south and east of the UK and we will pick up a NE / E air flow.  This air flow could stick around for much of next week.  By Tuesday things could be really cold in the upper atmosphere (1500m= -14C!). Down here in Reigate things will return to a wintry feel with hard frosts, cold temperatures around freezing and possible snow now and again. If the coldest upper air temps reach us then heavier snow from the E and NE is a possibility.  Tricky to tell this far out.  Brace yourselves and keep watching for updates!


Spring 2013 is likely to make some false starts in Reigate and the SE of England.  This week starting 4 March certainly looks warmer but more unsettled with some rain returning as Atlantic influences and LOW pressure take over as the HIGH drifts off south east over the continent.  It could reach pleasant max temperatures of 13ºC mid-week in a warm bath of southerly winds but these will be accompanied by some rain. The sketch map shows what models are predicting for Spring after this warm spell ends by this coming weekend.  The medium range charts see LOW pressure moving down over the continent and a ridge of HIGH pressure building back up to the north of the UK over the coming weekend.

march slide downThis could mean cool easterly winds returning from 9/10 March dragging temperatures back to rather wintry like figures by next weekend and beyond. Temperatures could take a significant fall, not as harsh as mid-winter, but certainly down to daytime temperatures of 5ºC again or perhaps even lower; in any case, much cooler than expected for March and possibly even cold enough to bring SNOW back on the agenda!  The north of the UK will fair better if this scenario pulls off update: cold plunge arrives from NE – which will be hit worst … anyhow, expect some ups and downs in the weather and a big false start to Spring.  


February 2013 weather in Reigate. Highest temp 11.6C; lowest temp -2.5C; rainfall total 42.6mm.

Also winter 2012-2013 summary available above too.

FULL update of RGS weather data available on the DATA page here!


Anti-cyclonic stratocumulus cloud continues to blanket Reigate and the SE of England in a cold, gloomy weather underworld.  A temperature inversion (where temperatures rise with height, instead of fall) at 1000 metres is trapping any rising air which inhibits convection spreading out the cloud mass to cover the entire sky: good to reduce rainfall, bad for any views of the sun!  Regrettably no light at the end of the tunnel yet: the north-easterlies circulating round the HIGH pressure to the North are likely to continue for much of the week and bring in blankets of stratocumulus cloud from the North Sea. This spectacular view from the EU Meteosat satellite today at midday clearly shows the cloud blanket voering SE England from 22,300 miles away.
Temperatures will struggle to exceed 5C in the days to come; this time last year temperatures were well above 12C and even hit 17C on a few days.

Here is a table showing the effects of wind chill, familiar to mountaineers.  The blue zones are what Reigate and the SE has experienced in recent days with gusts of 15mph in freezing air taking “feels like” temperatures down to -13ºC.  Note that this is the zone of “maximum” danger for hypothermia because people tend to underestimate the effects of any breeze in temperatures hovering around freezing and under-dress.  Note that a slight breeze is enough to cause the greatest chilling effect.  These cool and breezy conditions are also more common in mid-latitude populated areas like the SE of England where winter temperatures frequently hover around 0ºC.  Dry air feels colder than humid / moist air: there’s more evaporative cooling into dry air and dry air also conducts heat away from your warm body more readily than does moist air.

Met Office article on wind chill


Wrap up!  Spring is cancelled for at least another week!  Mainly dry but some light snow showers and a really cold wind will be around through the weekend for Reigate, albeit mostly very light snow flurries and with little or no accumulation. Air temperatures will climb slowly above freezing to 3ºC during the day but a stronger breeze of 15mph, gusting 20mph, will make it feel even colder, especially Sunday with wind chill as low as -6ºC during the day. Night air temps will fall to -3ºC.  A tad warmer and damper by mid-week with daytime temps rising to +5C; the HIGH shifts directly over the north of the UK so winds, still easterly or northerly, will be lighter and track more across the North Sea rather than central Europe: this will feel balmy in comparison! 


The cold easterlies predicted have created interesting and unusual cloud patterns across the country. The satellite photo from today shows ripples in the breaking cloud to the west of the hills in Wales and the SW.  The easterlies driving the cloud are part of the cold sinking dry air created by the anticyclone to the north east of the UK.  The easterlies are  forced to rise over the hills and then sink the other side (the “lee-side”), creating this wavy cloud pattern.
Another feature of this cold snap is illustrated in the video below which shows how temperatures have changed over the last few days.  Notice how inland temperatures drop significantly lower than anywhere near the sea. The sea stays warmer for longer during winter as it takes 5x longer to cool down (and warm up) than land surfaces.  The video shows temperatures rapidly falling to low temperatures inland but coastal areas are moderated by the warmer seas surrounding the British Isles.

The cold easterly winds and some light snow flurries will continue over the weekend as a weak short-wave trough (a “blip” in the isobars surrounding the HIGH) passes to the north of our region.  The very cold pool of upper air is drifting away to the south, so temperatures will recover very slowly through to Monday.  However, spring is certainly on-hold at the moment and, despite being a mostly dry week,  temperatures will remain lower than average in the continuing easterly air flow.  Watch next weekend as a low passes to the north of the UK which could bring a “last hurrah” for real winter conditions as a cold northerly is possibly on the cards.  Longer range forecasts give little cheer for us in Reigate and the South East as HIGH pressure seems to stick around to the North and bring in Channel lows to the south of the country bringing wet and cool weather.


This week for Reigate: dry and increasingly cold!  Watch the video which shows cold air (at 1500 metres) flooding in from the east.

Wind direction is so important in controlling our winter and early spring weather: many of the “source regions” (where our winds originate from) are at their most extreme at this time of year: the continental interiors, for example, are at their coldest and driest in late winter, so any air mass coming from the continent will be very cold indeed, despite Spring being just round the corner.  These cold and dry easterly winds contrast with our usual warm and wet SW Tropical winds that arrive from the Atlantic.  This week it is the turn of Easterly winds and HIGH pressure to dominate our weather: this means cold and dry.
UK unusual dry patchThe HIGH to the north east and the LOW to the south is a perfect set-up for dry and icy Easterly winds to flood across the South East, arriving from a very cold Russia on Tuesday and strengthening through to the weekend.  It should stay dry with a low risk of snow flurries reaching Reigate.   Actual max temperatures will be +1 or 2°C during the day but the 15 mph wind will make it feel very chilly at -3°C in the daytime and, during the night, as low as -8°C wind chill.  Cloud cover will control how low air temperatures actually fall at night: clear skies could see temperatures drop to -4°C with frosty mornings.  Want to warm up?  Get to Reykjavik in Iceland which will be the warmest city in Northern Europe this week with unseasonably high temperatures of +8°C with a “warm” and wet southerly Tropical wind.  Next week looks warmer and staying dry for Reigate with temperatures up to 10°C. An early taste of Spring perhaps?

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The impending LOW approaching from the NW this weekend is a real teaser!  It will track SE across the country and the centre of the LOW will pass to to the SW of Reigate sometime over Sunday night. It will then “stall” for a day or two and drag in cool winds from the East.  Fronts associated with this LOW will bring every type of precipitation known…probably!  A weakening warm front slowly drifting east across the country on Saturday is not likely to reach Reigate until the evening. Saturday will be cloudy, calm and cool but hopefully remain dry. The leading edge of the warm front could bring some light snow by Saturday evening.  Sunday will be the BIG ONE… wet, cold and miserable, all day. North of London there could be heavy snow.  Reigate is on the VERY EDGE of the forecasted snow area (see map). Temperatures will remain above freezing at up to 3-4C, too warm for snow. However, despite this, heavy rain could turn to snow any time.  From Sunday afternoon onwards a process called evaporative cooling could cause snowfall. Some raindrops always evaporate on their descent from clouds, even in really cold air. Evaporation (turning a liquid into a gas) uses energy / heat (think of how chilly you feel stepping out the shower; the cause = evaporation!). Now imagine millions of tiny raindrops evaporating, for every evaporating raindrop some energy (heat) is taken out of the atmosphere and lowers the air temperature. In marginal snow conditions this temperature drop can be sufficient to turn HEAVY RAIN (the more raindrops the more cooling) into SNOW, even if surface temperatures are above freezing.  So, the question for Reigate this weekend is not “will it snow on Sunday?” but “will it rain hard enough to snow on Sunday?”  Enjoy the precipitation anticipation!

Snow is very fussy. It requires particular conditions throughout the depth of the atmosphere to form. Any one of these conditions not met, and it will fall as sleet or rain. For example, snow requires particularly cold temperatures (obviously!) extending right the way up through the atmosphere to allow deposition of ice crystals instead of water droplets: indicator temperatures are lower than -27°C at 5500m, lower than at least -5°C at 1500m and surface temperatures at least below 2°C, so it doesn’t melt on the way down.  Also, a dew point below freezing is a pre-requisite for snow to fall. On Sunday and overnight to Monday not one of these conditions is met over Reigate, so snow in the current model forecast is not likely: 5000m temperatures are too warm (-25°C), at 1500m the temperature is a balmy +1°C and the dew point is +5°C through most of that period.  The only period when all the snow-forming conditions are met over Reigate (as things stand currently) is on Monday afternoon / evening.  Unfortunately, at that stage the LOW will have drifted off and taken much of the precipitation with it.  So… does this discount snowfall for Reigate over the weekend? Not at all, snow is still very possible because of nocturnal cooling and evaporative cooling and any slight change in the track of the LOW, but this is another story for later. Stay tuned!