Archives For snow

The US and Canadian winter storm is dominating weather headlines with London in Ontario, for example, recording -10c and plenty of snow. The jetstream looped wildly down across the US and Canada due to an “omega” blocking pattern in the Pacific causing a plunge of Arctic air to flow across the entire continent, almost reaching Florida at one point (but not quite!).27-11-2013 17-41-10


For the UK things are more benign.  This Friday 29 Dec sees a cool NW upper flow reaching the UK with a LOW moving over Scandinavia bringing down cool bright Arctic air for the weekend.  This is a rather interesting “cross-polar flow” which sees surface winds flowing right across the North Pole from Siberia / Pacific and reaching Reigate via N Greenland! It will warm up considerably over the N Atlantic waters which are still around 10c surrounding the UK but still only allow Reigate weekend temps of Tmax 5-7c with a cool breeze making it feel like 3-4c at best. Wrap up!

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After the weekend the HIGH keeps the south dry and relatively mild humid air (so cloudy) for the start of next week but it slips south allowing an increasingly brisk W/NW air flow. The main news is a possible significant cold shot from around Friday 6 Dec which will bring in much colder air across the whole country.  Models are currently coming into line on this and it is not certain how long or deep any cold snap will be but it seems likely that a cold snap will bring snow across northern and east coast regions while Reigate and SE will get some cold conditions with possible snow showers but cold wind and rain and sleety icy / wintry episodes are more likely for us. In any case, significant snowfall is not expected in the SE currently but periodic and overnight dusting on the hills in some v cold air temps is likely.  Frosty and icy conditions are coming for a while. Check back for updates though!

Dec 6-7 arrival of colder air

Dec 6-7 arrival of colder air

Spring 2013 across much of the northern hemisphere mid-latitude landmasses has been notable for extreme cold, record breaking snow falls and severe winter storms.  Northern Europe, Scandinavia, Russia, Western and North Canada, North and Eastern USA and NE China and Northern Japan have all been exposed to many more prolonged incursions of cold air from the Arctic than in “normal” years.  The blue and green colours on the temperature anomaly map above show areas experiencing a record breaking March of well below average temperatures (“anomalies”), some exceeding an average of 10°C below the temperature expected.  The map for 2013 year-to-date looks very similar, so the whole of late winter has been colder.  The satellite photo shows widespread snow across the whole northern hemisphere mid-latitudes: a good indication of how extra-ordinary this late winter has been.

So, what is responsible for this extreme late winter weather?   Here is a fun round-up of some of the main “suspects” on the Climate Cluedo board: which of them killed Spring 2013?  Click on each (as posted!) and find a quick judgement on their culpability in the death of Spring 2013! 

  1. Blocking high pressure / weaker jet stream
  2. Loss of Arctic sea ice
  3. Solar activity: sunspot cycles
  4. Volcanic eruptions
  5. El Nino / La Nina / ocean currents
  6. Long term climate change and orbital cycles
  7. Sudden Stratospheric Warming (started January)
  8. Human activity (to be dealt with later!)

Thought of some more suspects? Please leave a comment to add them!

Quick update Tuesday: This LOW is not now predicted to trouble UK Fri – Sat: it will not be the BLOCKBUSTER  we hoped might break through and bring milder conditions.  Instead, it’s a near miss to the South as the LOW skirts thru NFrance pushed aside by the Icelandic HIGH building once again to the North of UK. LOW to south WILL drag in more cold / cool easterlies through much of next week; so start of April will be cool but should be not quite so cold as now with daytime Tmax +6-7°C for Reigate.  Nights still frosty.  Mostly dry, poss of snow showers. No dramatic snow on the charts for Reigate at the moment. Point to note: Hekla volcano in S Iceland is seismically active: heightened eruption possibility. Hekla is not usually a show-stopper for air traffic and winds would blow ash away from Europe!

How and when will this record breaking cold weather end?  Models suggest the first week of April will still be cool but not quite as cold as now. The latest UKMO chart for the end of the week shows mild SW winds developing around a huge Atlantic depression and squeezing up against the cold air towards Southern England. The leading edge of fronts pushing up the Channel into southern England could bring snow for a time to the south, and possibly lots of it, as cold air undercuts the warm and forces it up.  The snag will be if these fronts stall for a while: the chart shows fronts parallel to isobars which usually means they are slow moving and could stick around, thus increasing any precipitation over areas underneath. Later models also show this LOW slipping to the south of the UK which will drag in more cool Easterlies for the start of April. Too early for details, could change… but this LOW may not be the blockbuster we all hope for to sweep away the cold!


WEATHER ALERT FOR UK AND REIGATE:

Saturday am: heavy snow falling across our region: check twitter for updates.  A major wintry weather event is unfolding tomorrow and over the weekend across the UK.  This could bring potentially hazardous weather Friday through Sunday almost anywhere in the UK so if you are travelling please take care and check weather warnings for your destination. Reigate remains comparatively sheltered throughout but even here we have the threat of seriously miserable and cold weather with an evil mix of heavy rain, cold winds and sleet turning to snow over this weekend.  Snow amounts and depths for us still uncertain though.

Cold Polar Easterly winds will increasingly undercut and push back the advancing warm air brought in by a vigorous depression out west in the Atlantic. Where these air masses meet is essentially where the heaviest rain and snow will fall: the fronts move north on Friday and then move south on Saturday as the cold air wins out over the warm: it is the move south on Saturday which could bring some SNOW to Reigate. The SW is due to get torrential rain, whilst anywhere north of the M4, especially on high ground, could see heavy snow and drifting in high winds. Reigate remains comparatively sheltered throughout this episode BUT if you are travelling anywhere else do heed weather warnings.
Whilst Reigate will escape the worst of all this, we are due to have a pretty cold, windy, very wet and sleety and at times snowy weekend weather wise!
Friday sees fronts crossing the country and bringing increasing rain to Reigate during the day. Overnight into Saturday might see this rain turning increasingly icy and sleety. Wind chill 0°C to -4°C.
Saturday will be a truly horrible day with temperatures falling throughout. Cold winds (feeling -5°C) and heavy rain will turn increasingly sleety and turn to snow anytime but with greatest risk in the afternoon.  By the afternoon, however, the heaviest precipitation should be dying out over Reigate so any snowfall should be light by that stage.  Saturday could see totals over 20mm of precipitation (mostly in the morning as rain); snow lying could amount from 0cm to a few cm especially on the Downs by evening. Any snow conditions will be worse to the north of the region and over high ground.
Sunday sees even colder weather and a threat of further snowfall from nearby fronts to the south.  Still uncertainty around this so keep watching forecasts. Wind chill -8°C so feeling very cold indeed.  Drier later though.
The rest of the week looks cold, frosty and dry with gradual recovery of temperatures and the hint of more spring-like temperatures next weekend!
Take care this weekend if you are travelling anywhere in the UK: floods in the SW, blizzards and snow up North. If you don’t need to travel, you should probably wait until Sunday or Monday when things have calmed down.

What a difference a year makes: check out the daffodil pictures: taken one year apart!

update Friday pm: much as stated above with main snow zone staying north of London for longer on some models: filthy horrible day mostly sleet icy rain Sat; poss light snow later pm as cold air arrives; cold wind; colder on sunday and into next week. Cold and frosty next week. #notspring 


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?)! 

Reigate is in an interesting location regarding the much anticipated snow tomorrow!  Whilst we will not experience anything like the metres of snow winter storm Nemo has delivered to Boston today, by Sunday evening Reigate is forecast to be on the edge of some exciting snowy weather to the north and east and in a superb position to watch events unfold as we sit on the battle front between warm (rain) and cold (snow) air!  It is due to rain most of the day on Sunday and turn to snow in the evening, initially and most significantly, over the North Downs.  Small gains in altitude could make a difference in whether you see snow or sleet or rain tomorrow: it’s that close! 

The LOW bringing all the uncertainty in the forecast is due to slip SE during tomorrow. It has warm air wedged between fronts to the south and west where precipitation will certainly fall as rain, some of it heavy.  On the leading edge of the advancing warm front, winds will turn increasingly Easterly during Sunday and drag in progressively colder air, especially over night into Monday morning.  This drop in temperature on Sunday afternoon is what will change any rain into snow /sleet.  By Sunday evening the warm front is due to be near Reigate but forecasts suggest it will stall and then slip south enhancing those cold easterlies but, at the same time, moving away the heaviest precipitation overnight which will peter out early Monday morning.  Temperatures will be above freezing throughout the day but only around 2 or 3°C, cold enough for evaporative cooling to create some local snowfall in heavy rain (see post yesterday).  Winds increasing to 30mph gusts in the afternoon will make it all feel thoroughly unpleasant.  Whilst rain and sleet are MOST likely all day, the zero-degree / freezing altitude decreases dramatically further north and east from Reigate.  Snow is therefore possible on the North Downs as even small increases in altitude locally could potentially add significant accumulations if we are positioned on the leading edge of the front for a period of time.  There is also a risk of snow settling lower down during Sunday afternoon and evening but temperatures are such that sleet seems most likely.  Total rainfall for the day is forecast to be up to 10mm so it will be a wet day regardless of how much snow falls.  Any snow falling in the evening could accumulate 2 or 3cm of snow, especially on the Downs.  So, to summarise, Reigate tomorrow is due to be increasingly wet and breezy as the day progresses, temperatures 3ºC, falling to 1ºC overnight to Monday.  Heaviest rain will be in the late afternoon / evening (6pm onwards) and this might turn sleety / snowy, especially over the Downs.  The forecast is full of uncertainty but, whatever turns out, do enjoy being in a pivotal meteological location tomorrow!  Meanwhile, scattered wintry showers are developing over our region this evening (Saturday).

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!

Reports of unusual “thunder snow” coming from NW England tonight with the passage of bands of heavy wintry showers moving south associated with a front. They appear to be dying out as they move South but might just still produce a heavy shower of snow or most probably sleet (as temps still 5°C and falling) over the Downs in the small hours. Unlikely to add up to much though and any showers should largely clear off by the morning rush, but take care of ice if driving later tonight. Surrey gritters are out.

It looks like February could see a return to winter conditions for Reigate (2 small colour charts) and maybe even cold enough for some snow; though with the sun being that bit stronger it is unlikely to be as chilly as last week. The jetstream, currently right over the UK and bringing our stormy conditions and unseasonably high temperatures (12°C today at midday in Reigate), is likely to be shifted south during the second week of February. A blocking upper ridge in the Atlantic and building HIGH pressure over the North Pole will combine to swing winds round to a cool northerly direction over the UK. A LOW over Europe will add to the chill by bringing in periods of cold Easterly winds over the UK as well and it is these which often bring significant snow to the South East.
Meanwhile, this week’s extraordinary weather is not over yet: a deep depression (see big synoptic chart) is forecast to rapidly swing up out of the SW on Friday. Depending on it’s precise track over the UK it could bring heavy rain and strong winds or EVEN some snow. The models disagree by a critical hundred miles or so: MetOffice has the LOW tracking south of Reigate= easterly winds = snow; GFS has it tracking north of Reigate = westerly winds = rain. (Update: UK Met Office model is now on it’s own with snow in the south; all other models take the track of the LOW further north leaving strong SW gales and rain on Friday but no snow for Reigate – snow will fall further north across the UK; so the synoptic chart above is probably WRONG already!!).  In both scenarios the back of this LOW will see nippy northerly winds bringing temperatures right down on Saturday, but at least it should be bright.

Beautiful satellite image of UK covered in snow