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Quick update for Friday and Saturday:

The Arctic pool of air brought down by the Northerlies through Thursday is due to develop into a cool pool of LOW pressure over the continent which will linger and flirt with the South East of the UK for this weekend. While the North and West basks under high pressure, the South is due for some cool brisk winds and some persistent rain at times this weekend: wind then rain on Friday, rain on Saturday. This will blow the cobwebs away (and some leaves!) after the balmy start to October. Significant rainfall total over 20mm on places.

se cool wash out

The wind starts first as a brisk cool Northerly on Thursday and Friday morning and then swinging round to a cool North Easterly during Friday with gales possible in the Channel and North Sea with 30mph+ gusts for Reigate. Friday pm will see the rain setting in, possibly quite late into the afternoon for Reigate. The rain is associated with complex fronts wrapped around the LOW pressure moving unusually SW across Northern France from the Netherlands. Once the rain arrives on Friday, it is likely to remain persistent until well into Saturday. Some significant totals are possible with moderate intensities on Saturday morning.  With the wind it will feel distinctly cool and autumnal compared to last weekend when 20c was exceeded in Reigate.

A Nor’easter is actually a storm off the coast of New York / Eastern USA which brings in cold blast of NE winds on the back of a depression circulation. This is like a mini-nor’easter but is tracking the wrong way.

 

Update: cool off will be a fall of 10c for much of the UK. Spot the difference below! These are Tmax temps: from high anomalies to October normal.UK cool down

The UK enjoyed being on the warm side of the HIGH this weekend and this will last for a day or two still.  However, a significant shift in the position of the HIGH pressure by models has placed it moving out WEST of the UK through this week leaving the door wide open for Arctic Air to spill out from Svalbard and make a dash for it down the North Sea. This air will be chilly! Later in the week the door closes on the Arctic but the cool air is left skulking very close to the SE in a LOW pressure of swirling showery cool air bringing rain threats to the East and SE. So while Reigate enjoyed 20c this weekend and some warm days Monday/Tues, by next weekend the best we can probably expect is half that, or thereabouts, and with heavy showers to boot.

arctic plunge

The HIGH moving west will have the effect of drawing down some brisk cold Arctic air directly from some islands called Svalbard (check out the web cam from today: this air is setting off our way very soon!) directly down the North Sea arriving in Reigate and the SE sometime mid-week having travelled across 2000 miles of gradually warming ocean surface, picking up heat and becoming UNSTABLE in its lower layers as a result.  Instability means heavy showers, drifting down on the chilly northerly breeze and threatening east coast districts and the SE. The cool pool of air will feed a LOW pressure over the near continent which will be cut-off as the HIGH topples over the North later this week, taking the jetstream and any warmer air, far to the North of the UK. The cool pool cut-off LOW thus produced is likely to bring showers to the East coast and SE England and lurk about for some time.
The HIGH in the Atlantic, meanwhile, is effectively blocking any movement of these systems and the weather is likely to stay put for sometime, gradually warming through but producing convective showers as it does so.

This blocked weather pattern with weak westerly winds and HIGH pressure moving slowly or not at all, is characteristic of the very negative North Atlantic Oscillation showing up at the moment.  Northern blocking and HIGH than normal pressure over the Arctic with lower than normal pressure over the Azores, allows Arctic and Polar air to leak out and flow south over Europe and the UK.  This was what brought our COLD late Spring 2013.  Is this happening again this year?

An interesting development which continues to back up several indicators that are showing the potential for a COLD winter ahead.  Salt and snow shovels at the ready! The chart below is a monthly averaged CFS seasonal prediction for February 2014 anomaly air mass temps: how far above or below temps are from the 30 yr mean.  Europe, on this chart, looks v chilly (but these temps are for 5000feet, not surface!).  This is not, however, a forecast, merely an indication.  These charts also flip-flop quite a bit so we need to check them regularly to get an idea of patterns.  So far, the cool pattern is prevailing.

feb 2014 anomaly

Weather Watch: update: heavy rain overnight Friday, moving away am; even HEAVIER rain overnight Fri – Sat, moving away am. Some possibly torrential and totals poss exceeding 30mm in next 48 hrs. 

The second significant Autumnal gear change is looking more certain for early next week as a big LOW sweeps between Iceland and Norway across the North of Scotland and a brisk active northerly jet combines to drag in a breezy and cool Arctic airmass from the Poles all the way across the UK.  The isobars on UKMO charts can be traced all the way back to the Poles, so expect chilly weather… possibly creeping into the low teens and feeling like 10c in the wind.

fri fronts

The process starts on Friday as fronts bring potentially heavy rain across the South, including Reigate, especially Friday pm and overnight into Saturday morning. The situation is complicated with fronts lingering over or near the south throughout the weekend so expect rain, some heavy, almost anytime during Friday through to Saturday. Saturday will be cooler than Friday.

The real news, though is the temperature plunge next week. Keep posted for more on this Autumnal development.

There might be a glimmer of some warmer temperatures returning by 21 Sept as a high builds from the SW … temps of low 20c’s might be expected to make a return but certainly not a heat wave!

A cool LOW pressure tracking across from Greenland and Iceland will move over the UK on Friday and sit over Reigate for the weekend and into much of next week. Atlantic depressions usually have some warm tropical air circulating with cold polar air but not this one!  With high pressure to the west any warm SW air flow is being blocked out, leaving Reigate on a “cold-washing-cycle” with mostly swirling cold polar air circulating around the low. Cool air coupled with low pressure even in this cool Spring weather causes unstable airmasses.  Instability means that big showers can develop as thermals rise from warming surfaces even in the weak Spring sunshine we are experiencing.  Convective thunderstorms are a remote but interesting potential risk for Reigate over the weekend.
Various fronts and troughs will circulate around the LOW pressure which is blocked by a HIGH over Scandinavia and E.Europe and won’t move much. The LOW will bring showery rain, some of it heavy with the possibility of hail and even thunderstorms, especially over the weekend (50% chance of convective thunderstorms on Sunday over Reigate).  Temperatures will never climb much above 7°C and, with gusty winds of over 30mph, it will feel cool, but nothing like what we had earlier this week. Some models predict a return of cold Easterly winds as the LOW slips south over the UK and drags in cold continental air again. There is still uncertainty about this but it will certainly be an unsettled week. Other models see glimmers of spring after around the 23 March as winds turn more SW and a ridge builds over the country bringing drier conditions.  More on this later, keep your fingers crossed!