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Winter 2020-2021 Prediction for the UK


iapennell
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Posted
  • Location: Manchester Deansgate.
  • Weather Preferences: Heavy disruptive snowfall.
  • Location: Manchester Deansgate.

    Yes, I would leave the back end open but there is nowhere near enough evidence for 'A winter of two halves' type prediction, just wouldn't have the whole of Feb nailed down as mild either that is all, anyone who thinks Dec is going to deliver now is in cloud cuckoo land.

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    Posted
  • Location: Medlock Valley, Oldham, 103 metres/337 feet asl.
  • Weather Preferences: Cold, snow, thunderstorms, warm summers not too hot.
  • Location: Medlock Valley, Oldham, 103 metres/337 feet asl.

    Cheers Ian. Not what most on here including myself wanted to see but we'll see how it all pans out.

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    Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria
    17 minutes ago, Frost HoIIow said:

    Cheers Ian. Not what most on here including myself wanted to see but we'll see how it all pans out.

    Sadly, and I speak as one who likes hard frost and snow myself, the fundamentals in the large-scale circulation and the pattern of sea- surface temperatures just do not point towards any real spells of wintry weather affecting the UK this coming season. However, if one like gales and heavy rain and lives anywhere north-west of a line from Bristol to the Humber there will be no disappointment! 

    It would be nice to be proved wrong with my forecast, but I am (sadly) confident that I will not be. 

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    Posted
  • Location: Wantage, Oxon
  • Weather Preferences: Hot, cold!
  • Location: Wantage, Oxon
    3 hours ago, iapennell said:

    Dear Readers,

    I have, as promised, got a long-term 2020-2021 forecast for the United Kingdom based on information that I have about global and regional sea-surface temperatures, large scale upper wind patterns and the current phase of the ENSO cycle in the Equatorial Pacific.

    Firstly, the Quasi Biennial Oscillation. This is a (roughly) 27- month cycle of wind- fluctuations high up over the Equator - in the Equatorial Stratosphere. Wind levels at  the 30 mb level averaged near 8 metres per second from the West and at the 50 mb level were just over 2 metres per second from the West during October 2020. These Westerlies gradually descend and enter the tropical troposphere about two months after their occurrence at the 30 and 50 mb levels in the Equatorial Stratosphere, then over the next few weeks impact on the entire global circulation- mainly affecting the winter circulation. This transfer of Westerly momentum from the Quasi-Biennial Oscillation circulation- magnified as air moves into higher latitudes would imply stronger higher-latitude Westerlies (of 2 to 3 mph) during  January and February.

    Currently there is a Lá Niña type circulation in the Pacific Ocean resulting on sea-surface temperatures about 1 to 2C cooler than the seasonal norm from the West Coast of South America right across to the Western Pacific (Polynesia area). Other things being equal cooler-than-normal waters along the Equator around at least one third of the Earth's circumference ought to result in weaker north-east Trade Winds from the Northern Hemisphere arising from a weaker Hadley Cell. However, the Equatorial Atlantic and Indian Oceans are 1 to 2C warmer than usual, which would lead to greater convection along the Intertropical Convergence Zone (ITCZ), a stronger Hadley Cell, and stronger north-east Trade Winds from the Northern Hemisphere. There is therefore a small net effect of hotter-than-usual conditions beneath the (likely) winter position of the Intertropical Convergence Zone leading to a stronger Hadley Circulation and (therefore) greater transfer of Westerly atmospheric momentum into higher latitudes of the Northern Hemisphere. Moreover, with this setting, relatively cool waters over the eastern and central Equatorial Pacific lead to stronger easterlies near the surface of the Pacific (where winds blow west from the cool waters where surface pressure rises towards hotter seas across the westernmost tropical Pacific). That leads to greater Westerly atmospheric momentum transfer into both the Northern and Southern Hemispheres aloft. 

    The North Atlantic is substantially warmer than usual at present, whilst early snowfalls have resulted in Canada cooling down fast. Arctic sea-ice levels remain below normal but are recovering quite quickly from record-low levels seen during October 2020. Arctic ice-cover is recovering fastest in the Canadian Arctic but large areas north of Norway and Arctic Russia remain ice-free to date (if Britain is to have very cold north and east winds, due to blocking patterns further north it's best to have ice-growth north of Norway and northwest Russia): A very cold Canada and Greenland, but a warmer than usual North Atlantic sets the scene for a strong atmospheric temperature and pressure gradient across the far north-west Atlantic, one that would favour deeper North Atlantic depressions and a strong North Atlantic jet-stream heading towards the United Kingdom.

    In the shorter term, both the fact of a continuation of an exceptional North Atlantic hurricane season, and fact that the upper winds in the stratosphere high above 60N are predicted to be stronger than usual out to 16 days' hence by all 31 atmospheric modellers (http://weatheriscool.com/) points to strong Westerlies heading towards the UK throughout the following month (and covering the Christmas period). The circulation in the stratosphere above 60N takes two to three weeks to impact on the weather near the surface across northern Europe and North America. 

    The Sun is still in a quiet phase at the start of Sunspot Cycle 25, among other things that ought to mean a cooler Sun, a sluggish Hadley Cell and less transfer of heat and Westerly atmospheric momentum into higher latitudes. However, the deep tropics are still warmer than usual and the Westerly QBO in the Equatorial Stratosphere will have other impacts. There are also signs that the Sun is becoming more active in any case (see here: https://www.nasa.gov/feature/goddard/2020/new-sunspots-herald-increased-solar-activity-cycle-sdo and here: https://earthsky.org/space/photos-sunspots-ar2781-solar-cycle-25 ) . If, as seems likely, the Sun is growing active it will be stronger and produce more heat to power the Hadley Circulation -and cause more warmth and Westerly momentum to shift to higher latitudes. Lingering hurricanes and typhoons mean that strong easterly winds to the north of them (and westerly Atmospheric momentum being thrown northwards aloft) will also contribute to a greater transfer of heat and Westerly momentum into higher northern latitudes- leading to stronger Westerlies in higher latitudes in the run-up to (and over) Christmas.

    The conclusion of this analysis is a dire one for lovers of snow and hard frost, since all these macro-scale influences on Britain's prospective winter- weather weigh heavily towards Winter 2020-2021 being a mild, wet and (yes) potentially stormy one. This is particularly likely, since the strength of the south-westerlies through November has prevented the advance of continental snow-cover westwards of the Ural Mountains. This, along with the persistent south-west flow will prevent very cold air and snow-cover building up over Scandinavia an north-west Russia (crucial if strong blocking highs are to form in the area). It is, instead, eastern Canada and Greenland that have the intense cold and snow-cover, which will help generate some intense North Atlantic baroclinicity and cyclogenesis.

    The North Atlantic, being warmer than usual, will also limit the likelihood of really cold air reaching the UK. Sea surface temperatures around Britain are warmer than normal after a slightly milder than usual autumn overall and (even were there to be a fortnight of very cold northerly or easterly winds, which is very unlikely) sea- surface temperatures around Britain will remain warmer than usual. This will ameliorate the impact of any cold air-streams from north or east. 

    For a bit more detail to my prediction December is likely to be dominated by persistent south-westerlies, with plenty of wind and rain. Stormy conditions can be expected during the second half of December across Scotland, Northern England, Northern Ireland and North Wales. There will be snow in the mountains at times, interspersed with mild strong south-westerlies that remove all traces of snow (except perhaps on Ben Nevis and on the Cairngorms). The south of England will be drier, but still quite windy. Temperatures of 15C can be expected on some days in the South and Midlands. Frost at night will be rare except in northernmost mountain areas.

    January 2021 will continue the wet- and at times- stormy theme. Expect something like January 2014- it will be cold enough for snow at times in the uplands of Scotland and across Northern Britain, but don't expect widespread snowfall across the lowlands. There will be some frosty nights with clear spells following colder west- northwest winds, but nothing of any severity anywhere. The Midlands and South will get the driest and brightest weather, and with mild south-west winds at times air temperatures will still reach 13C widely.

    February 2021 will continue the unsettled theme, but it will not be as wet and stormy as in February 2020. With Canada and Greenland by this time very cold and the north Atlantic approaching its coolest, February will bring the highest chance of any cold weather. Tropical cyclones will be happening by then in the Southern Hemisphere (over the Indian Ocean and western Pacific south of the Equator where the seas will likely be very warm by then); these will by this time impact the general circulation in the Northern Hemisphere in the opposite manner to hurricanes north of the Equator- as the Easterlies high up on the equator-wards side of these Southern Hemisphere tropical cyclones will enter the Northern Hemisphere circulation, this time reducing Westerly Atmospheric Angular Momentum: This will lead to some weakening of the Atlantic Westerlies. Thus, we can expect a week of more of dry fine weather with colder north-westerly winds, which may become easterly as the high-pressure drifts into northern Europe. This will mean widespread night frost for a time and some bright cold days. However, a nationwide severe wintry spell with lots of snow is not at all likely as the fundamentals will still be against this- the Westerlies are likely to shift north of Britain across the still relatively-warm Norwegian Sea so this will preclude frigid Arctic or Siberian air reaching these shores. The best likelihood of seeing any snow will be in the mountains across northern Britain with the squally colder Westerlies following the passage of depressions.

    So to conclude,  a mild rainy, windy and unsettled Winter 2020-2021 with snow in northernmost mountains at times, with the best chance of brighter colder weather in February, looks to be on the cards.                    

     

    Thanks Ian.

    Actually, December is the month I most disagree on, I think there is a good chance of blocked patterns until the strat and trop vortexes connect this year, which could deliver some cold spells, agree that January will be wet mild and windy.  February will depend on SSW or not, so much so, that we can’t hazard a guess at that month yet.  We will see...

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    Posted
  • Location: Longden, Shropshire
  • Location: Longden, Shropshire

    Thanks Ian and good to see you posting.  Not what I wanted to read but not surprised either!

    Edited by Don
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    This forecast is completely the opposite to other Winter forecasts for the UK - 2020 /21, I have, seen. 

    It looks like December will begin cold by day, frosty by night and dry - certainly not beginning with your prediction of a month "dominated by persistent south-westerlies, with plenty of wind and rain."

    Time will tell though. 

     

     

     

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    Posted
  • Location: Hounslow, London
  • Weather Preferences: Csa/Csb
  • Location: Hounslow, London

    Prediction for here...

    December

    Avg max: 9c
    Avg min: 2c
    Rain: 40mm
    Snow: n/a
    Sun: 50 hours

    January

    Avg max: 9c
    Avg min: 4c
    Rain: 60mm
    Snow: 1 day falling, 0cm settling
    Sun: 50 hours

    February

    Avg max: 10c
    Avg min: 3c
    Rain: 30mm
    Snow: n/a
    Sun: 90 hours

     

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    Posted
  • Location: Hounslow, London
  • Weather Preferences: Csa/Csb
  • Location: Hounslow, London

    My prediction is the prediction for my area, where winter highs average around 8-9c with lows of 2-3c. Not sure where the confusion is coming from.

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    Posted
  • Location: Rotherhithe, 5.8M ASL
  • Location: Rotherhithe, 5.8M ASL
    2 hours ago, B87 said:

    My prediction is the prediction for my area, where winter highs average around 8-9c with lows of 2-3c. Not sure where the confusion is coming from.

    I think he’s talking about the OP as for your London forecast I see December being below average.

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    Posted
  • Location: Wakefield, West Yorkshire
  • Weather Preferences: Anything except blazing hot summers!
  • Location: Wakefield, West Yorkshire
    11 hours ago, B87 said:

    My prediction is the prediction for my area, where winter highs average around 8-9c with lows of 2-3c. Not sure where the confusion is coming from.

    You weren't being quoted 😉

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    Posted
  • Location: NR Worthing SE Coast
  • Location: NR Worthing SE Coast

    December forecast already bust which is good news if you are looking for a colder December for a change.

    A very well written forecast,but shows you that long range forecasts are a waste of time,especially when trying to forecast colder weather.

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    • 2 weeks later...
    Posted
  • Location: Hounslow, London
  • Weather Preferences: Csa/Csb
  • Location: Hounslow, London

    It looks like my December prediction might be accurate temperature-wise. Cold spell is out of the way and the average currently stands at 6/2, with average or above average temps for the forseeable future.

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    • 4 weeks later...
    Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria

    It is a pleasant surprise to have a bit of an easterly for the next week, the fundamentals that I used in my Winter forecast- Westerly QBO, above- average sea-surface temperatures over the North Atlantic but very cold Canadian/ Greenland Arctic but warmer-than-normal Siberian Arctic (in November) did not suggest a Sudden Stratospheric Warming in early January over the central Arctic. Unfortunately it is likely to be relatively short-lived (see the weather chart for 18th January 2021):

       image.thumb.png.1829be60e680c8a4a2b0a718415a8ff6.png

    And -7C looks set to be the coldest we will get in the North Pennines (about the 10th January- we regularly used to get below -10C in the 1980's) :

    image.thumb.png.d477ebeb2f58983c56b9f86bdb2246dc.png

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    Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria

    For cold snow-and-hard frost lovers (I count myself amongst them) it does not look like high pressure is going to remain extensive enough along the North Norway to North Russia axis (nor for long enough) to give the ultra- frigid -40C air over Siberia a chance to get as far west as the UK. The long-term charts suggest the North Atlantic Westerlies will re-assert themselves by about the 16th January. Although Stratospheric winds are very much Easterly (on average) at 60N on 18th January (offering a hint of something icy in February), mean winds are predicted to be over 20 mph (10 metres/ second) from the West on average at the 250 mb level along 60N on the 18th January.

    However, it would be great if those Arctic Stratospheric Easterlies happening (and predicted) did lead to some truly dramatic intense frost and snow: Unfortunately, the warmth in the Norwegian Sea, sea-ice below normal on he Russian/ Scandinavian side of the Arctic and the Himalayas failing to act as a sufficiently big sink for Westerly Atmospheric Angular Momentum to absolve more of the need for Westerlies over the North Atlantic and North Pacific to counterract the tropical and sub-tropical Easterlies (there have been 20 mph Westerlies on the Tibetan Plateau recently- they need to be stronger) means that whatever cold is likely to reach the UK is likely to have a) a short fetch to the north/east and b) liable to be swept aside by mild North Atlantic air. However, I would like to be proved wrong on this as winters devoid of hard frost/ heavy snow do rather fail to inspire me (and indeed many others who visit this Forum)!  

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    Met Office long range into very early a February, suggests that air flow over North Sea from Scandinavia and that meeting up with milder air to the south of UK could set up a possibility of substantial snow, where the two air masses meet. 

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    Posted
  • Location: Manchester
  • Weather Preferences: Winter: Ice days, clear skies, blizzards. Summer: cool and dry
  • Location: Manchester

    Already it looks like this January will be cold, possibly colder than 2013 if the effects of the SSW come into play

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    On 02/01/2021 at 16:16, iapennell said:

    And -7C looks set to be the coldest we will get in the North Pennines (about the 10th January- we regularly used to get below -10C in the 1980's) :

     

    I think I heard on the local news, that Ravenseat in The Yorkshire Dales, had a low temperature of minus 11C  a few days ago. 

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