Archives For rainfall

A stubbornly slow moving “dishwasher” LOW spinning up west of Spain and just NE of the Azores has been abandoned by the jetstream. This LOW has sat there all week in a cool pool near the Azores. The tropical Azores have seen Tmax temps only a tad higher than Reigate this week as a cool polar pool gradually fills in that region. It is the position of the Atlantic dishwasher that controls our weekend weather.
Most models agree it will edge closer but this is a slow stuttering move without purpose or direction. Infact, it’s likely that this LOW will never move across the UK because of the stubborn ridge of HIGH pressure to the NE, causing the LOW to remain stuck out west sending occasional fronts and heavy showers our way as the pressure falls. The UK will remain in a relatively warm upper southerly flow with Tmax staying into the 20s through the weekend and possibly into next week, though things are uncertain at that range at the moment.
Expect windier conditions through the weekend, especially to the south coast.
Weekend weather could possibly see thundery showers edging over Reigate sometime Saturday through to Sunday but this is dependent on the location of the LOW. Current model runs suggest the heaviest rain will stay south in the Channel but check back as updates occur.
Between now and then… sluggish, overcast high pressure days with anticyclonic gloom for much of the week until the wind picks up.
Reigate was, again, the warmest place in the UK today… at 23.7C matching a rounded up figure for Charlwood, Gatwick at 24c.

Reigate weekend weather will be windy and wet first thing Saturday with showers and bright intervals following after a well defined front moves away early. Typically, no deluge is forecast for Reigate and the East but early rain on Saturday could be heavy for a time around breakfast. Most rain will fall further west. The most significant feature of weekend weather for Reigate will be wind: gusting from the west over 35mph at times on exposed hills on Saturday, less on Sunday.  

A summer depression with a LOW central pressure for the summer (994mb) is passing straight across Scotland over the weekend. This has winds spiralling anti-clockwise around the centre of the LOW, for Reigate this means gusts over 30mph on the hills and generally widespread 20mph winds. Quite a breezy day for mid-summer. As the cloud breaks in the afternoon it will be good kite flying weather. More rain and cloud could be widespread on Sunday, some of it heavy and showery in the afternoon.
For next week things look much better as a large HIGH pressure builds across the entire Atlantic and pushes any more depressions well to the North over Iceland. This HIGH will settle over the west of the UK and build across the East as the weekend LOW moves out into the North Sea. We can look forward to some pleasant dry summer weather well into next week, reaching over 20C. But always with the threat of a shower in the east where winds will be from the NW or west.
So…total rainfall for the next week in Reigate is forecast to be a mere 10mm or so, hardly very much. At least 8mm of this is forecast to fall this weekend, making next week very dry indeed!

During the recent last spell of warm humid sticky weather with the warm southerly plume of potentially thundery downpours, Reigate got no showers at all! The capped inversion layer prevented any significant convection.  Despite immensely high forecast CAPES and lifted index, each forecast would predict heavy showers and potential thunderstorms but none would arrive as the last model runs would lower capes and LI.  Below the inversion, with no significant convection to break the cap, cloud simply spread out into dull strato-cumulus formations covering the sky and reducing the warming by the sun and the instability of the lower layer of the atmosphere was therefore reduced.  No cap was busted, no spectacular cumulonimbus were seen round Reigate.  Some occured nearby in Kent and the Channel and running up the N Sea.  Several models (NMM, GFS, NAE) consistently predicted showery rain almost everyday, some of it heavy, yet none arrived.  Other models were nearer the mark and picked up better on the lack of powerful convection beneath the inversion (UKMO, HIRLAM).  So, in Reigate, being so sheltered and pleasant, it never rains but it pause!

Reigate weekend in brief: Saturday dry (but v wet North England: low risk of it extending our way); Sunday wet; Monday showers NE wind.

Update: forecast for weekend proved v tricky: Model rainfall forecasts struggled with the easterly cut off low set-up.  Saturday was pleasant and Sunday turned out dry and warm. Note: GFS rainfall seems not to cope well with meridional jet stream with cut-off low over UK scenario!

Wondering if the weather is a bit odd recently? Well, you may have it right… the weather is literally upside-down from what we would normally expect in the UK. We would normally expect LOW pressure systems to whizz over the country from west to east. Temperature normally decreases further north and we usually expect warm air to arrive from the south. This weekend turns this normal expectation upside-down! A WARM air mass is pressing down from the NE, having arrived on a long journey from the Mediterranean and Eastern Europe (where there is a heatwave). This warm air is due to meet the COOL polar air hovering over the UK and cause torrential rain over Saturday up North. Reigate will see none of this and will stay mostly dry on Saturday.  On Sunday, however, cooler air will push up from the South and cause heavy rain for the SE and Reigate. Warm air from the North?  Cool air from the South? Slightly unusual. 

warm frontWhere air masses of different temperatures meet the warmer air is forced to rise up and over the cool: a front.  The greater the difference in temperature between the air masses and the steeper the temperature gradient, the greater the uplift.  This causes condensation, clouds and rain.  Fronts usually approach the UK from the West.  Currently a huge HIGH pressure is blocking all westerly winds.  A warm front moving south from across the North Sea is most unusual!

The cause of all this is the development of a cut-off LOW over Europe. A very looping jetsream (meridional) has been drawing polar air down across the UK this week and this cold air has pooled up over Western Europe, hence all the convection and showers. Meanwhile, the jet stream anticsnorthward moving limb of the jetstream has been dragging warm air up over Eastern Europe (which has a heatwave).  This warm air is due to meet the cool air over the UK this weekend.
The good news is that Reigate is likely to have a reasonable Saturday out of all this. Sunday could be pretty wet though.
The cut-off LOW will hang around for early next week and the unsettled theme continues for us in Reigate until the end of next week when things could improve for Bank Holiday as HIGH pressure builds in from the Atlantic. This means the west and north are likely to see better weather than the SE for Bank Holiday, but that’s a long way off to be certain. Keep tuned!


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!

Rainfall is usually measured in millimetres but it is hard to imagine how MUCH WATER this actually means. It is easier to use the idea that 1mm of rainfall is equal to 1 litre of water falling on every square metre of ground.  Friday is going to be a wet day with 10mm of rainfall expected.  But how much water is actually going to fall on the school during this wet day? Here’s how to find out:
1. Use Google Earth to plot a polygon.
2. Right click on the polygon file in the Places list on the left hand side of Google Earth and COPY it.
3. Find http://www.earthpoint.us/Shapes.aspx
4. PASTE the polygon file into the empty box mid-page.
5. Select sq metres for the area units and click “view on web page”.
6. This brings up the AREA of your polygon in sq metres.
7. Now multiply the area by the expected or actual amount of rainfall in mm.
8. The result will be the litres of rain falling on that area.
On Friday we can therefore expect about 200,000 litres of rain to fall on Reigate Grammar School. This is about the same as 11,000 buckets or 650 car fuel tanks being emptied onto the school grounds during the course of the day.
Weather advisory: bring an umbrella!
Update: in the end, the actual rainfall only delivered 6mm of rain onto RGS… the LOW pressure didn’t pep up to form the awful winter storm forecast earlier in the week. Friday turned out to be wet in the morning and then cleared up to be a nice day.  Nevertheless it still added up to 6000 buckets of water thrown over the school!