Archives For March 2013

Here is a summary of the causes of the March 11 2013 “Channel Blizzard” which brought extra-ordinary “Spring” weather to SE England and the Channel Islands and N France. At RGS we had record low wind chill temperatures of -10°C at 9.30am, 36mph gusts and sub-zero temperatures all day.  Follow the numbers on the map to get a quick view of why it all happened!

1. Cold source region for Polar Air: the NE winds originated from the Polar regions with temperatures below -15°C and traveled across an extremely cold continent to reach the UK.

2. On their journey, the North Easterlies warmed a little over the North Sea (by now +4-5°C) which caused showers to form in unstable air (warming causes air to rise, clouds form and it snows). These showers formed lines called “snow streamers” which fed snow to the SE for most of the day and into Tuesday morning.

3. Much warmer SW winds at +10°C met the frigid cold Polar air mass somewhere over the Bay of Biscay but they didn’t mix well and they certainly didn’t get on!  In fact, the cold, dense polar air pushed the lighter, less dense tropical air right up off the ground, to over 4000m, where all the moisture condensed, formed cloud and snowed!  The high winds experienced across SE England were “squeezed” like toothpaste between the HIGH over Iceland the LOW over France (a high “pressure gradient”: look how close together the isobars are over SE England and the Channel!).

4. Next? Things will stay cold during mid-week as the UK remains firmly in Polar air and enjoys some dry weather courtesy of a HIGH over Iceland (unusual).  Clearer skies and frosts.  However, a Polar Low forming SE of Greenland at the moment is due to break through the Icelandic HIGH later in the week and bring unsettled conditions to the end of the week / weekend: as Polar air is still involved this may bring further snow and sleet.

Greenwich Lightship is a UK Met Office weather station in the middle of the English Channel. 3 metre waves, 50mph winds, sow and 10 foot waves were recorded.  Unbelievably horrendous conditions which the Channel Islands experienced as a blizzard.

Watch the satellite animation below and spot the storm winding up in the Bay of Biscay before it hits the Channel and says “Hello” to France and the UK!

A severe blizzard in the English Channel will brush perilously close to Reigate today and overnight. Sub-zero temperatures for the next 48 hours and strong gusty easterly winds of >20mph will make it feel like -10ºC and potentially much lower (see wind chill charts posted earlier).  Whilst the UKMet-Office model refuses to bring any significant snow to Reigate other weather models certainly do!  In fact, some forecast as much as 10cm of snow to our region falling later Monday and overnight especially. With cold temperatures and strong winds this snow will blow around and be very unpleasant indeed, and could amount to 10cm, especially south and east, less west and north.  Updates @RGSweather on twitter.


Sunday final analysis update: crossing the Channel Monday?…be warned of v cold blizzard conditions!  LOW centre set to track thru N France most likely bringing only light snow to Reigate Monday morning but increasing risk of significant accumulation later in the day and overnight into Tuesday.  Any shift further north in the fronts could bring heavy snow to S counties pm.  Latest hi-resolution NMM model (below) shows light snow showers all day but risk increasing to heavy snow pm extending into southern counties of England, reaching Reigate late pm or evening….; UKMet Office predicts the least snow of all the models.V V tricky forecast.

So: Reigate forecast for Monday-Tuesday: emphasis on bitterly COLD, snowy day with extreme wind chill for (any) time of year with a low risk of heavier snow later and overnight to Tuesday, especially for places further South. so…accumulations 0 – 10cm by Tuesday am.

sunday 06Z NMM model

Cold weather alert! Reigate should prepare for an impressive weather change this weekend into next week.  The temperature will drop like a stone over Sunday night: shown by these Reigate maximum temperatures at midday on Saturday max +11ºC, Sunday max +5ºC, Monday max -1ºC with wind chill even as low as -18ºC (yes) possible in forecast 40 mph gusts in exposed places.  Winds will average 20 mph but even this will cause wind chill of -8ºC.  It will feel cold on Monday!  Light snowfall could start Sunday pm and continue overnight through to Monday. It may seem odd, but this snow will be caused by warm air from the South over-riding the frigid COLD Polar air blasting in from the NE: meeting at a front.  Check the temperature height diagrams to see how this works: warm, moist air circulating around the LOW in the Channel will be undercut by the dense freezing cold polar air from NE. The warm air forced to rise causes cooling, condensation, cloud formation and, as upper air temperatures are so cold… SNOW is likely to fall. Possible accumulations Sunday – Monday around Reigate could be 0-3cm (higher figures on hills) and more possible to the south of the region where precipitation could be more intense nearer the fronts.  So…positioning of the LOW is critical.  The snow maps give an idea of potential snow areas in the south on Monday.  There could be light snow showers on and off in Reigate and another moderate fall is possible Monday pm as the LOW tracks nearer to the south east of our region.  It will feel cold in strong gusts from the East: wind chills down to an outrageous -18ºC are theoretically possible if you are caught in strong easterly gusts with air temps below 0ºC all day. Temperatures will actually fall through the day on Monday as the Polar air takes a grip.  Lowest temperatures all winter are possible overnight Monday-Tuesday. Hopefully, this weather change will not take anyone by surprise: it has been on the cards for over a week and flagged up here on 2 March. The rest of the week will remain cold, but feel less cold in light winds, and drier with pressure building from the north, but more snow might precede rain later in the week as things warm a little next weekend.  More updates later as details emerge for Monday which is still v changeable!


Reigate is at risk from heavy rain moving north across the SE during Friday pm through to Saturday. 24 hour rainfall totals could exceed 30mm for this period. This marks the start of an interesting period of weather seeing temperatures taking a big drop from Sunday through to Monday. Prepare for cold temperatures and icy conditions in Reigate by Monday through to Tuesday especially. Snow is a risk but exact details remain uncertain: the main snow risk for Sunday is north of London, Midlands and north of the M4 corridor but temperatures fall overnight easily low enough for any rain round Reigate to increasingly fall as snow. It will certainly be chilly and Monday night could be extraordinarily cold for March (where’s Spring?)! 


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!

HIGH pressure means air sinks, warms up as it descends and dries out: this should mean less cloud… right? Unfortunately not always. Reigate has seen very little sunshine in the last few weeks despite a persistent HIGH pressure. Stratocumulus cloud and stratus cloud has hung low over the North Downs. This low cloud has been trapped by a temperature inversion at 1000m, where temperatures rise with height putting a “lid” on the weather. Any rising air will hit this inversion and convection will stop. Clouds forming beneath the inversion will simply spread out, join up and cover the sky: creating overcast dull gloomy conditions. Once the cloud forms it is difficult to shift because, whilst the sunshines above the cloud warming the air, the cold air persists below exacerbating the inversion. A stronger breeze or drier air or a shift in the position of the HIGH will release us from this weather underworld. The good news is the weekend looks brighter with winds less likely to be blowing from a cool, damp North Sea. Sunday looks the brightest with temperatures reaching 9 or 10C by the afternoon: almost spring like. The rest of the week from Wednesday will become more unsettled, feeling warmer but wetter as the HIGH at last moves away to the south east allowing Atlantic westerlies back for a breath of wet air!

To Spring… early forecast models suggest wetter conditions with slightly below average temps for the south of England with possible frequent easterly winds as LOWS track to the south; and drier, warmer and slightly above average conditions in the north of the country.  Essentially HIGH to the north and LOW / jet stream to the south of the country which will keep the south cooler and unsettled with the north enjoying better weather.  In short, more of what we had in late winter, just a warmer version?! Updates later.