Winter 2017/2018-Stormy December, Two Severe Wintry Spells January/February.

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This coming winter (2017/18) there are global (macroscale) influences that suggest that the UK will have some colder spells of weather. This does not mean a cold winter by any means, just that there is a stronger signal for cold spells (related to blocking over northern Europe), likely to occur during January-February 2018.  There are six significant global-scale weather-patterns that will have an influence on the weather in the coming months:

1)     The Quasi Biennial Oscillation (QBO) has turned Easterly:

This is a wind-pattern high up over the Equator, affecting the Equatorial Stratosphere that gravitates from westerly winds to easterlies, then back to westerlies over a (approximately) thirty-month period. After an unusually long period of westerlies winds have become strongly easterly at the 30 mb level (about 38 mph as averaged through October).  At the 50 mb level winds are still Westerly but are now very light (just 3 mph as averaged through October) and these winds are likely to become easterly this month (November 2017).  These strong easterlies high up in the Equatorial Stratosphere are a source of negative Westerly Atmospheric Angular Momentum –or AAM for short (that is, winds blowing from east to west, rather than west to east) and its impact- once the easterlies of the QBO descend and impact the general global circulation- will be to resist (and weaken) the upper westerlies that move polewards aloft over the tropics and subtropics- and then go on to weaken the Westerlies aloft and near the surface in higher latitudes. Weaker Westerlies coming into north-western Europe mean less storms and a higher likelihood of high-pressure being able to form in high latitudes sending icy north or easterly winds towards Britain.

However, one must not over-estimate the likely impact of the QBO on weather in Britain, the air at the 30 mb level is just 0.03 times the density of air at sea-level, so the 38 mph easterly would only slow down surface westerlies by just over 1 mph. Also, the easterly QBO air will mix (eventually) with the vast bulk of the atmosphere globally- further reducing its impact. But the impact is greater when the slowed-down upper westerlies reach higher latitudes (because of the reduced distance to the axis of the Earth’s rotation); hence there is likely to be a discernable impact on Britain’s weather. It takes two to three months for the easterly QBO winds at 30 mb to descend, enter the global circulation and then reach higher latitudes in its impact: Thus the signal from the strong easterly winds high up over the Equator will affect Britain as weaker intermittent westerly winds (with icy winds spilling out from northern Europe at times) during late January/ February.

Other influences on the winter weather-patterns affecting the UK may well have a greater impact, as mentioned the QBO plays out in the rarefied atmosphere (at 10 to 50 mb level) high over the Equator and the proportion of the total global circulation directly involved with the QBO is small.

2)     El Niño Southern Oscillation (ENSO) has entered a weak La Niña Phase:

La Niña watch (12^th October 2017) predicts a weak La Niña during winter 2017/18, with below normal sea-surface temperatures for the east and central Equatorial Pacific Ocean with sea surface temperatures a little above normal in the far western tropical Pacific Ocean.  The impact of cooler than normal Equatorial waters would weaken the low-pressure zone of hot rising air near the Equator, thus weakening the north-easterly trade winds blowing into it from the Northern Hemisphere: Consequently  the Hadley Cell weakens and westerlies aloft further from the tropics (including the subtropical jetstream and- further north- the Arctic Circumpolar Vortex are weakened in turn). Again, this suggests weaker westerlies reaching northwest Europe, increasing the chance of cold frosty spells associated with blocking highs over Scandinavia.

By way of contrast, the strong El Niño of 2015/16 contributed towards winter 2015/16 being exceptionally wet, mild and stormy in the UK.

However, one must not over-estimate the likely impact.  A weak La Niña means conditions are not so far removed from normal.  Furthermore, La Niña implies stronger easterly Trade Winds over the central and eastern Pacific Ocean (to push cool waters westwards into the central Pacific Ocean) along with stronger easterlies aloft coming across the northern (Equatorial) Andes of Ecuador and Colombia: These would result in more Westerly AAM being added to the global atmospheric circulation- resulting in a tendency towards milder stormier winter weather along western continental margins in higher latitudes; the pattern of  cooler than normal Equatorial waters off South America and steamy waters in the far west (near Indonesia) would also tend to encourage stronger easterly winds across the Equatorial Pacific Ocean.  However, it is mostly the south-east Trade winds blowing off northern South America that impacts the ENSO cycle; if these are stronger and causing La Niña the excess Westerly AAM is liable to affect the Southern Hemisphere atmospheric circulation rather than the Northern Hemisphere, leaving the cooler waters to weaken the Hadley Circulation and the north-east Trades that deliver Westerly AAM to the Northern Hemisphere atmospheric circulation. That being so, it means La Niña, even a weak one, would lead ultimately to a small weakening of winter westerlies reaching north-west Europe.

The available literature on La Niñas suggests a tendency towards cooler drier conditions for north-west Europe in the winter months (see here “La Nina may chill Britain in run-up to Christmas” (http://www.weather.com) and here  El Nino and La Nina- The Weather Outlook (https//www.theweatheroutlook.com/two)): This backs up the prognosis that I have just made. That said, the La Niña this coming winter is expected to remain weak, impacts on the UK will be small.

3)     The Madden Julian Oscillation (MJO) is weak:

The Madden Julian Oscillation (MJO) is a large-scale tropical pressure and wind-pattern that affects the tropical oceans; it propagates eastwards at the rate of 10 to 15 mph per day and circulates right around the world in a period of two months on average.  It is, of course, modified by the ENSO Phase, the relatively cool tropical Pacific waters associated with La Niña (as is the case this year) tends to weaken the MJO Cycle- and this is indeed predicted to be the case over the next couple of months.  The MJO is hemispheric in its phases- when one hemisphere of the deep tropics has increased convection and rising air the other hemisphere of the deep tropics has weak convection and even subsidence that would suppress rainfall.

For the next month the MJO is predicted to be weak, but may strengthen a little as the large active (convective) zone moves (or reforms should it be totally swamped by La Niña) over the tropical Atlantic in late January/February (the position of the convective area dictates the Phase of the MJO). Phases 7 and 8 are when the convective zone is over the tropical Atlantic Ocean and if the MJO is fairly active in these phases it increases the likelihood of blocking patterns over Northern Europe.  Atmospheric waves associated with an active MJO in any phases can penetrate upwards into the Stratosphere- and this can lead ultimately to possible stratospheric subsidence and associated Sudden Stratospheric Warmings over the Arctic: That in turn encourages a sharp weakening (and expansion) of the Circumpolar Vortex and much colder winter conditions affecting north-west Europe (source: http://www.cpc.ncep.noaa.gov>mjoupdate).

The phase and intensity of the Madden Julian Oscillation may (slightly- in view of how weak it will be) increase the likelihood of some very cold weather from the east or north-east affecting the UK in late January and February- but it is likely to have almost no overall impact on the first half of the season.  On the whole, the MJO Phase may have more of an impact than either the weak La Niña or the easterly QBO from mid-January onwards, but certainly not before then.

4)     The current Sunspot Cycle is drawing towards an end as the Sun goes Quiet:

The Sun is entering a quiet phase with few sunspots and solar flares:  In the process the energy output from the Sun is also declining slightly compared to recent years.  It is known that high levels of Sunspot activity combined with solar flares and coronal mass ejections (CMEs) result in high speed plasma crashing into the Sun-facing side as this hurtles westwards at 66,660 miles per hour as the Earth orbits the Sun (65,600 mph taking into account the Earth’s rotation from west to east).  Thus these solar winds crash into the atmosphere from rather westwards of vertical and impart Westerly AAM to the global circulation- leading to a spike of deep depressions associated with stronger Westerlies in higher latitudes, especially in winter (“Clear link between solar activity and winter weather revealed”, October 2011, https://phys.org>Earth>Earth Sciences).  The Sun is, of course, entering a quiet phase and, notwithstanding the large Solar Flare that affected Earth in September, expect little solar activity overall this coming winter: Less Solar Flares and CME’s mean less of the forces that would increase Westerly AAM and (with it) strong Westerlies in higher latitudes.  This is yet another factor that favours a slightly increased chance of colder drier weather from the east this winter.   

As the Sun enters it’s quiet phase nearing the end of the current Sunspot Cycle, total solar output has been declining slightly:  The Solar Constant was 1362 Watts per square metre on average during 2014, now it averages under 1361 Watts per square metre with dips to 1360 Watts per square metre (Source: Solar Irradiance and Sunspot Numbers, http://www.climate4you.com>Sun). This is a drop in total solar irradiance of 0.1% or more, one that would cause a global temperature drop of 0.1˚C (other things being equal), but nearer 0.2˚C (and greater in high latitudes) once positive feedbacks are taken into account.  The additional greenhouse effect arising from the increased CO2 levels over the last three years (about 10 ppm) does not even half counter such a sharp drop in solar output. Slightly reduced solar output in itself would lead to a weakening of the Hadley Circulation in the tropics and subtropics, with slightly weaker north-easterly Trade Winds at the surface (and weaker westerlies aloft). This weakening of the Hadley Circulation would result from the 0.1% drop in solar irradiance, whether the drop in solar output led to an overall global cooling in the face of rising CO2 levels- or not. The weakening of the Hadley Circulation may be slight, but it would also lead to a weakening of the higher-latitude westerlies.  Again, that means there is a small increase in the likelihood of severe cold reaching the UK from Russia this winter. 

The impact of the Quiet Sun with a 0.1% reduced Solar Constant has perhaps the most potent impact on the coming winter of the global climatic drivers so far discussed; yet for reasons to be discussed below this does not by any means guarantee a season like 2009/10 or 2010/11.

5)     Arctic Sea-Ice remains below normal but not by much, whilst the North Atlantic Ocean and North Pacific Ocean are 1 to 2˚C warmer than the seasonal norm in early November

Arctic Sea-Ice extent was overall below the normal for early November by about 1.4 million square kilometres and the southernmost extent of the pack-ice is some 250 km north of its seasonal position to the north of the Bering Strait and in the Barents Sea/Svalbard area. However, sea-ice extent is close to the seasonal normal extent in the Davis Strait and the Canadian Arctic Archipelago. (Source: Arctic Sea-Ice News and Analysis http://nsidc.org/arcticseaicenews/).  Sea surface temperatures in early November were 1 to 2˚C warmer than the seasonal normal across the North Atlantic (http://weather.unisys.com>surface>sfc_daily/), about 1˚C warmer than usual across the North Pacific.  However sea-surface temperatures are up to 4˚C warmer than normal in the Bering Strait between Alaska and eastern Siberia and up to 5˚C warmer than normal off the East Coast of the USA.  Sea surface temperatures are actually up to 1˚C cooler than normal across much of the Equatorial Indian Ocean, parts of the Equatorial Atlantic as well as 1 to 2˚C cooler than normal for the time of year over the eastern Equatorial Pacific Ocean.  By way of contrast, the subtropical North Atlantic and subtropical North Pacific sea-surface temperatures are above the long-term seasonal norm, again by about 1˚C for early November, sea surface temperatures are also about 1˚C above normal in the Norwegian Sea. The pattern of warmer than usual sea-surface temperatures in both the North Atlantic and North Pacific, with the Arctic-ice limit further north than usual in the European Arctic is supportive of the Circumpolar Vortex- the river of very strong westerly winds in the upper atmosphere over higher latitudes- being contracted and blowing closer to the Arctic.  There is still likely to be ice-cover over the Arctic as this expands in extent going into winter to ensure the Arctic interior gets extremely cold by the time we reach December (i.e. below -25˚C at the surface and colder still aloft); this with warmer than usual oceans in mid-latitudes will intensify the atmospheric temperature and pressure gradients that drive sub-arctic depressions and the strong westerlies that blow on their southern flanks.  Furthermore, unusually warm waters off the USA Eastern Seaboard combined with sea-ice extent and that of severe cold near normal extent around north-east Canada will help foster an intense atmospheric temperature and pressure gradient that could help send some really powerful depressions headed across the far North Atlantic, to bring strong mild south-westerlies to the UK. 

On the contrary there are cooler than normal sea-surface temperatures over Equatorial waters but slightly warmer than usual sea-surface temperatures across the northern sub-tropics: This would  substantially weaken the crucial temperature gradients that drive the Hadley Circulation; since the normal 35˚N to Equator lower-atmospheric temperature gradient is about 15˚C averaged over the Northern Hemisphere in winter the sea-surface temperature anomalies (such as they are) are likely to lead to a weakening of the Hadley Circulation by up to 5% This means weaker north-easterly Trade Winds, and with the Circumpolar Vortex likely to be north of its seasonally normal position (due to reduced Arctic ice-extent and warmer-than-usual mid-latitude oceans) the subtropical high-pressure belt is likely to be 35 to 40˚N with the slightly weaker north-easterly Trade Winds covering a somewhat greater area of lower/tropical latitudes than usual, westerlies in higher latitudes would not need to be any stronger to provide a sink for the westerly atmospheric angular momentum generated by more extensive (but weaker) north-easterly Trade Winds. 

Despite all this, the fact that the Westerlies are likely to be blowing in higher latitudes (due to warmer mid-latitude oceans and reduced Arctic ice extent) means these Westerlies will be blowing closer to the axis of the Earth’s rotation; thus they will need to blow stronger to provide a sink for all the westerly Atmospheric Angular Momentum (AAM) caused by the north-easterly Trade Winds and high-latitude (Polar) Easterlies.

However, snowcover and severe cold over the interior of Asia could help displace the strong Westerlies (at least aloft) to the extent that the Himalayas and Pamirs become a major sink for Westerly AAM; then all bets are off with all factors likely to weaken the mid-latitude Westerlies combining to cause a Sudden Stratospheric Warming over the Arctic: This we will now discuss.

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1)     Snowcover over Eurasia is at a greater extent than normal for the time of year, but it is not as great in extent as this time last year.

Eurasian snowcover can, if other factors are right, lead to high-latitude blocking and much colder weather reaching north-west Europe in winter.  Snowcover extent is so far above normal over the Eurasian landmass, but not to the extent it was in early November 2016. Snowfalls in early winter over the Eurasian continental landmass leads to greatly accelerated seasonal cooling as a fresh powdery snow-cover reflects up to 85% of the weakening solar insolation- with the result that solar warming is virtually eliminated and long-wave (terrestrial) radiation cooling continues as in an extended night. The resulting strong cooling encourages the air to shrink with the result being that surface pressure rises and the resulting high-pressure keeps skies clear: This has the effect of enhancing the strong radiative heat loss so the low atmosphere rapidly becomes extremely cold- and dense- ensuring an intensification of the surface high-pressure.  However, this process only unfolds over a wide area if the Circumpolar Vortex is not so strong that westerly winds off the North Atlantic continue to push deep into Russia, the Ukraine and Kazakhstan- either preventing temperatures falling low enough for snow to fall and lie unmelted or bringing milder air that melts the results of earlier snowfalls. There are indications that, as we head towards December that the westerlies off the North Atlantic will strengthen and push back cold air and thaw established snowcover over much of Scandinavia and westernmost Russia.

In January, with the westerlies coming into Europe are likely to weaken a little, for some of the reasons hinted at above: Eurasian snowcover is likely to re-establish itself right across from Vladivostok westwards to Bergen and Berlin in the west when that happens.  With pan-Eurasian snowcover and strong surface cooling across the continent, strong high-altitude westerlies will  impact the Himalayas (with a resulting heavy loss of westerly AAM); weaker North Atlantic westerlies result and Scandinavian high-pressure has a higher chance of becoming established to bring much colder weather to the UK.

 

With all this in mind, we can flesh out what the winter, particularly the latter stages of the season, may be like.  The second half of November and into December is easier to predict on the basis that the long-term forecast models do provide stronger indications of what is likely to happen.  We look at these now:

GFS and GFS.EPS modelling covering the Stratosphere over the Arctic and down into mid-latitudes predicts the likely strength of the Stratospheric Westerlies over and around the Arctic for a fortnight ahead and (because the Stratospheric Westerlies change fairly slowly on a day to day basis) this gives an indication of conditions up to a month in advance since wind-speeds and directions in the Arctic stratosphere take about ten days to a fortnight to work down through the troposphere and impact on large scale weather-patterns.  Currently, the Stratospheric Westerlies- at both the 10 mb and 30 mb level- averaged along 60N are stronger than normal and are predicted to become even stronger- and remain significantly stronger than normal by the 25^th November. The centre of the Vortex is predicted to be over Svalbard/Jan Mayan Islands for much of the next fortnight, with a trough into northern Russia at times- for both the 10 mb and 30 mb levels. This translates into deeper depressions and stormier weather to be expected for the end of this month and as we head into December 2018 (Source: Stratospheric Forecast Data: http//www.weatheriscool.com/). The fact that Stratospheric temperatures over the UK are predicted to be frigid (often -65˚C or colder) with the Stratospheric Arctic Vortex shifted this side of 80N at times, with the trough over northern Russia- gives a hint that colder west or north-westerly winds will intersperse the expected stormier December. This is certainly likely to be the case in Scotland.

More immediate forecast modelling suggests that whilst the second half of November will be increasingly stormy that there will be a couple of short cold spells with north or north-westerly winds bringing Arctic air south across the country.  Wetterzentral’s ensemble modelling suggests another spell with north and north-west winds for 17^th to 22^nd November, with high-pressure likely to move in from the west over the following few days; Meteocentre (Canada) ensemble modelling had a pronounced spell with Arctic winds 17^th to 21^st November with high-pressure over Britain by the 22^nd whilst the Met Office longer term outlook hints at northerlies for 18^th-20^th November and (thereafter) a strong hint that high pressure will bring clear cold conditions with night frost interspersed with more unsettled spells with possible snow in the North from late November through to early December (Source: http://www.weathercharts.org/).  The BBC longer-term outlook also suggests high-pressure moving over the UK for the end of November and into December 2017, but hints that confidence in the different forecast models is low.  To that end, I would concur that the strong Stratospheric Westerlies encircling the Arctic along 60N (with mean speeds at 10mb predicted to be 70 mph at times) will in all likelihood be making their presence felt lower down in the troposphere as we get into December 2017.

With the information at hand regarding the shorter term outlooks, coupled with the condition of ENSO, the Sunspot Cycle, easterly QBO developing, MJO, Eurasian snowcover, Arctic sea-ice extent and distribution and sea-surface temperatures we can now produce a forecast for Winter 2017/18 for the united Kingdom.

The Winter 2017/2018 Seasonal Forecast for the United Kingdom.

November 2017

On the basis of the above information, the remainder of this month is likely to be characterised by short spells with milder westerly winds and some rain, particularly in Scotland and North West England; these mild spells will be interspersed by much colder northerlies that will bring widespread night frosts and the first snowfalls of the winter to land above 250 metres’ elevation across Scotland, North Wales, Northern Ireland and northern counties of England.  The South and Midlands, along with South Wales is likely to be dry and bright during these cold spells, showers will be light and unlikely to be as snow except on the highest ground of (say) the Brecon Beacons, Dartmoor, Exmoor and the Peak District. The period from 20^th to 23^rd November is likely to be particularly cold with much of Britain experiencing the first really hard night frosts of winter, with minima of -4˚C or lower and snow can be expected to fall and lie for a few days across much of lowland northern Scotland in addition to the uplands (where blizzard conditions may be expected for a time with both day and night temperatures below freezing point).

During the short milder spells with westerly winds daytime temperatures will be above 10˚C with night temperatures several degrees above freezing point across the lowlands of the entire United Kingdom and in the South maxima above 13˚C can be expected on a couple more days.  During the cold northerly spells maxima will be around 7˚C in the South but only 2 to 4˚C in the lowlands of Scotland, Cumbria and Northumberland and night frost will be widespread with even coastal locations in South Wales and southern England getting their first air-frosts of the season.

As high-pressure in the north-east Atlantic moves east over Britain from the 23^rd November expect a few days with clear skies, light winds and further night frost- possibly with freezing fog developing as well. Daytime temperatures will be 6 to 7˚C in the lowlands with weak wintry sunshine, though it will remain much colder where fog fails to clear. This settled spell is chiefly likely to affect England and Wales only.  Scotland will become more unsettled, with stronger westerly winds as the currently very strong Stratospheric Polar Vortex starts to make its presence felt: However, winds will be westerly rather than south-westerly (though still strong, with gales at times)and unsettled will not mean mild.  Further (heavy) snowfall is likely to affect the Scottish Mountains at times with cold wet conditions in the lowlands,- daytime temperatures will be around 7˚C over lowland Scotland during this unsettled (westerly) last week of November.  For England and Wales, damp westerlies will return at the end of the month, though these will be milder (and less strong) than the Scottish westerlies: Temperatures are likely to recover to around 11˚C by day in southern England at the month’s end.

For November 2017 as a whole, average monthly temperatures will range from around 7.5˚C along the South Coast of England and costal South Wales to 6.5˚C across the Midlands, lowland Lancashire and North Wales, to around 5˚C across much of lowland Scotland.  Rainfall is likely to be below normal across the Midlands, southern England, South Wales, Yorkshire and North East England- some of these areas will get less than two inches’ moisture for the entire month.  Rainfall totals will be close to the seasonal normal across Scotland, Cumbria and North Wales.

December 2017

The strength of the Circumpolar Vortex, the currently above normal sea-surface temperatures over mid-latitude Oceans and just enough Arctic sea-ice extent to ensure Arctic interior will  be very cold by then (but with the sea-ice margin north of the usual position) will be defining influences on the month’s weather. The impact of the developing easterly QBO in the Equatorial Stratosphere will not have affected our weather:  It’s certain that the subtropical high-pressure belt will be centred 35 to 40˚N across the North Atlantic into the Mediterranean, as the north-east Trade Winds weaken in response to the weakening Intertropical Convergence Zone (the ITCZ) moving south over cooler-than-usual Equatorial waters;  the current set-up of sea-surface temperatures and sea-ice margins in higher latitudes will still be there and this will give scope for the subtropical high and the north-east Trade Winds to extend further north than usual for December. Unusually warm waters off the US East Coast will persist to give scope for intense cyclogenisis due to the temperature gradient between these waters and what will then be a very cold north-east Canada.

These factors together limit the scope for high-latitude blocking during December.  The month will be dominated by deep depressions racing east-north-east from Newfoundland towards Iceland.  These strong westerlies will bring rain, gales and relatively mild temperatures across the UK with regularity and daytime temperatures of 10˚C or even higher will be common across the English and Welsh lowlands during the month: However winds will be westerly rather than south-westerly and colder air will affect Scotland and Northern England at times, these will bring snowfalls to the hills with snow lying above 300 metres’ elevation. There will be a couple of occasions during December when a deep depression moves towards Norway and winds veer to be north-westerly to bring cold weather across the whole country; snow showers will affect low ground across Scotland and the North (with daytime temperatures around 3˚C) but with brighter conditions and maxima around 6˚C to southern England and air-frost will be widespread across the country at night.

Early in December, high-pressure is likely to make its presence felt for a few days, at least for England and Wales: Weak wintry sunshine will dominate chilly days with maxima close to 6˚C across the lowlands whilst frost and fog (freezing in places) will be widespread at night.  Scotland is likely to miss out on this dry spell with strong westerly winds bringing chilly rain at times to the lowlands but periodic blizzards to the mountains.

The Christmas period is likely to be particularly stormy, arising from a Stratospheric Vortex reaching maximum intensity in December. Gales and heavy rain will sweep the country at times (severe gales will affect western Scotland), but it will be cold in Scotland as sub-Arctic air gets into the mix. Heavy snow will affect the Scottish mountains and snowfalls will also occur on the hills of the Lake District and the Pennines at times.

For December as a whole, average monthly temperatures will range from near 6.5˚C on the South Coast of England and in South Wales to around 5˚C across the Midlands and Lancashire and just 4˚C in northern Scotland. The Scottish mountains, anywhere above about 600 metres will have a mean temperature below freezing point and snow-cover- established in late November is liable to persist (and accumulate) during December. Rainfall during December will be near average over the Midlands, South-East England, the North-East and Yorkshire but well-above average over North and West Scotland, North West England, Northern Ireland, North and West Wales and South West England.

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January 2018

The easterly QBO, a weak influence from the JMO with its active cell reaching (or relocating to) the tropical Atlantic and changes in the atmospheric circulation over the entire Eurasian landmass following a further increase in pan-continental snowcover are increasingly likely to impinge on the weather affecting the UK this month.  However the intense baroclinic temperature and pressure gradient between a warmer than normal North Atlantic and a frigid Arctic (especially the Canada/Greenland Sector) is likely to hold sway to bring a continuation of the stormy, if chilly, conditions from where December left off- at least during the first half of the month.

Strong westerly and south-westerly winds will therefore predominate during the first half of January, bringing rain and gales across the country. Scotland and Northern Ireland will bear the brunt of the rain and gales, but these conditions will also affect England and Wales.  Daytime temperatures will range from 10˚C by day in southern areas of England and South Wales whilst maxima in the Scottish lowlands will be near 7C.  Snow will still fall regularly in the Scottish Mountains during this period; however snow showers will also accompany occasional colder incursions from the north-west across the Scottish lowlands, North-East England and the Lancashire and Yorkshire lowlands (with heavier snow in the hills). Frost will be widespread at night when skies clear following the colder snaps from the north-west.

During the second half of January global (macroscale) influences on our weather are likely to lead to a weakening of the North Atlantic Westerlies. A couple of other factors not mentioned above make this likely- firstly the return of the Sun to the Arctic Stratosphere after a couple of months’ total darkness will lead to some warming there (this is an influence that would help weaken the tropospheric Circumpolar Vortex going forwards). Secondly, tropical cyclones in the Southern Hemisphere will start to occur regularly-moving along the ITCZ in its reaches south of the Equator by then; strong easterlies aloft on the equatorwards side of such tropical cyclones enter the Northern Hemisphere circulation helping to reduce total Westerly AAM in the Northern Hemisphere. This coming January, with various factors coming into play that would encourage weaker higher-latitude Westerlies (aloft and at the surface), these additional changes set the scene for much colder weather to reach the United Kingdom late in the month.

To that end, I am predicting that there will be a ten-day period when conditions will become much colder as the wind backs to easterly as the Circumpolar Vortex weakens dramatically. High-pressure will become established over the European Arctic and a frigid current of air will be drawn westwards across all of Western Europe from a bitterly cold snow-covered Russia.  With the Mediterranean Sea still warmer than usual (current seasonal anomaly +2˚C) this would encourage depressions to form along the baroclinic boundary between a cold Europe and warm Mediterranean, strong westerlies on the southern flank of these depressions will further alleviate pressure on the North Atlantic to be a major sink for atmospheric Westerly AAM. Other North Atlantic depressions will be steered northwards towards Svalbard and the Barents Sea, helped by warmer-than-usual waters in this area and the temperature contrast between these waters and the frigid Greenland Ice-cap.  This will set the scene for high-pressure over Arctic Scandinavia to intensify and bring the first really severe wintry spell to the UK for five years.

The very cold ten day spell in late January will therefore be characterised by easterly or north-easterly winds: These will bring light snowfalls to eastern coastal districts of England and Scotland although heavier snow will affect England and Wales as fairly modest (rather than deep) depressions move into the Bay of Biscay at times. Scotland is likely to miss out on such snowfalls, except those near the East Coast, because of its proximity to high-pressure over Scandinavia but it will still be very cold here. Across the UK daytime temperatures are likely to remain below 0˚C once the cold air is well-established; with largely clear skies at night minima will fall below -5˚C across the country and inland locations across the Midlands, Yorkshire and Scotland will drop below -10˚C on at least one night. Temperatures will be even lower where skies clear over snowcover and winds fall light; minima below -15˚C can be expected in the coldest frost-hollows.

I predict the bitter cold will come from the east rather than due north because the temperature patterns, sea-surface temperature patterns and the likely strength of the Circumpolar Vortex suggests a three-wave pattern (with a ridge anchored to the Rocky mountains). This places the upper ridge over Western Europe, which is not where it needs to be if we are to get a Greenland High and a trough to the east of Britain that would encourage northerlies.  A not-too-strong Circumpolar Vortex with an upper ridge over Western Europe is much more likely to foment high-pressure over Scandinavia- with the trough to the south-east encouraging depressions to form in the eastern Mediterranean.  This is just the pattern that would set the scene for a spell of icy easterlies from Russia.

As the south-westerlies from the North Atlantic re-assert themselves at the end of this very cold spell and the Scandinavian High retreats to Finland there is likely to be a period of heavier snowfall across Scotland and northern England as mild moist air pushes up over the frigid air at the surface. There may be a short spell of snow further south before this quickly turns to rain (this may be freezing rain for a time as the moisture falls on still-frozen pavements and roads).

For January 2018 as a whole I predict temperatures to be close to the long-term monthly normal in most places; the English Midlands, South East England and Yorkshire will be a little colder than normal with a mean temperature close to 3˚C. Upland areas of the North Pennines and Scotland will have mean temperatures at or below freezing point and these areas are likely to retain a snowcover for most- if not all- of January. Rainfall totals will range from well above normal in north-west Scotland and Cumbria to a bit below normal across Yorkshire, the Midlands and South East England. Rainfall will also be a bit above normal in Wales, North West and South West England.

February 2018

The factors that are likely to contribute to the cold spell predicted in late January will still be there in February; if anything these influences will be stronger. The full effects of the current strong easterly QBO at the 30mb-level high over the Equator will have reached high latitudes in the Northern Hemisphere and very cold air (with snowcover) will be entrenched across Central and Eastern Europe as a result of earlier Scandinavian blocking. The Sun will be quiet and weak La Niña conditions are still likely to be present in the Equatorial Pacific keeping the Hadley Circulation weaker than it might otherwise be. Wave activity associated with the (weak) MJO could ultimately lead to stratospheric subsidence over the High Arctic, further weakening the Circumpolar Vortex going forwards.  Severe cold is likely to be entrenched across all northern and central Asia; this can only ensure that the Himalayas will remain a major sink for Westerly AAM as strong upper Westerlies blast them. All of this suggests one further episodes with high-pressure over Scandinavia and bitterly cold easterlies affecting Britain is likely to occur.

Against that, we have Arctic Canada becoming extremely cold (-30˚C) by early February; with sea-surface temperatures still likely to be above normal further south-east in the North Atlantic this will encourage the formation of deep depressions that are likely to head east-northeast over the North Atlantic to pass south of Iceland. This is likely to bring about a return to mild wet weather affecting Britain.  When eastern Canada gets very cold and sea-ice forms around Newfoundland this also encourages an eastward propagation of the ridges and troughs associated with the Circumpolar Vortex, as well as strengthening it.  Any blocking over Scandinavia is liable to be swept eastwards.

To that end, I am predicting that February will be punctuated by one further spell with bitterly cold easterly winds from Russia, associated with strong high-pressure over Arctic Scandinavia: This bitterly cold spell will occur early-mid February and last about ten days.  These will be more pronounced than the late January affair with any North Atlantic depressions kept well west of Britain and with the North Sea chilled considerably after the January cold spell less snow is likely to affect the East Coasts of England and Scotland. The airstreams reaching Britain will still be very cold and with clear night skies likely to be the norm severe night frosts will occur nationwide with minima falling to or below -10˚C over a wide area.  Daytime temperatures will struggle to get above freezing point (though days will be largely dry and sunny), even in the South West and in South Wales once the bitterly cold Polar Continental airmass is well-established temperatures will struggle to get above 0˚C: In the coldest upland areas of Scotland, North East England and Yorkshire (where snowcover is likely) daytime maxima may not exceed -5˚C on the coldest days, whilst nights will be extremely cold (locally as low as -15˚C).

During the second half of February the Scandinavian High will get pushed into north-west Russia as the North Atlantic flow (encouraged by the intense atmospheric baroclinic gradient between Canada and the NW Atlantic) strengthens enough to allow depressions to pass between Iceland and Scotland. This will mean mild south-westerly winds returning to the UK and with the help of the strengthening late-February Sun will ensure daytime temperatures of 11˚C or more will occur across the South of England and South Wales. These south-westerly winds will not bring a great deal of rain to the English Midlands and to counties from Sussex to County Durham as a consequence of high-pressure ensconced across Europe, however Scotland and North West England will have some heavy rain and the south-westerlies will often be strong. Daytime temperatures in lowland Scotland will typically be near 8˚C during the mild second half of February with blustery south-west winds; it will still be cold enough in the Scottish Mountains for further snowfalls during the second half of the month.

Milder south-westerlies will also affect Britain at the start of February, between the frigid easterly spell of late January and that of early/mid-February: Again these will bring rain and strong winds to Scotland and NW England, whilst East/SE England has more mild brightness and less rain.

For February 2018 as a whole I expect that overall mean temperatures will be a little below normal across Yorkshire, North-East and South East England, including East Anglia: In this area the bitterly cold easterlies will arrive earlier, be colder and hang on longer than further west- mean daily temperatures for February as a whole will be near 3˚C in the lowlands of these regions of the UK. Further west temperatures will be close to the long-term February normal though westernmost Scotland, Northern Ireland and South West England (where the mean monthly temperature will be about 6˚C) will be a little warmer than normal overall. Rainfall is likely to be below what would be expected in February across most of the country, with East Anglia and lowland parts of Yorkshire and the East Midlands likely to see little over an inch worth of rainfall during the entire month. On the contrary Western Scotland and Northern Ireland will have rainfall amounts close to the long-term February norm.

For Winter 2017/2018 as a whole, I am certainly not predicting a colder than normal season overall across the country (though parts of Yorkshire and Eastern England may average a little below normal the South West of England and South Wales will be a little milder than the seasonal norm overall), but it is likely to be drier than usual for the season in the South East and in counties of Eastern England (including Yorkshire and the North East) but wetter than usual in Western Scotland and NW England.

[MP-R]

A fascinating read as always Ian! Thanks for taking the time to put it together. Certainly not liking the sound of December, but I suppose there is always the likelihood of W-NW zonality with more of a Pm influence in the mix like December 2014. January and February sound a bit more interesting though.

[Don]

Thanks as always for a detailed forecast, Ian.  I will not be too unhappy if it comes off, after the last few winters we have had to endure!

Edited November 11, 2017 by Don

[cheshire snow]

Great read Ian

Thanks for the time and effort

C.S 

[lassie23]

Might as well tell everyone in the MOD thread to pipe down and not bother until mid January

[hillbilly]

I have to admire your passion in detail Ian but I am sceptical of any foreast beyond 2 weeks so much so I don' know wether to laugh or cry.However I wish you luck with your prediction and if it predicts correct we can all come and worship you.Personally I don' give predictions but with a string of mild winters we are due at least an average one or one cooler than of late.The maths says we have to have something cooler so it will probably be the mildest winter ever recorded.

[Walsall Wood Snow]

Doesn't sound too bad at all. If we get those predicted cold spells it would defiantly be the best Winter since 2012/13, as long as there was a good dumping of snow at some point. 

 

Edited November 12, 2017 by Walsall Wood Snow

[Nick L]

The precise predictions at 2/3 months out are bold, I'll give you that...

[Radiating Dendrite]

A nice read with some good research but pure fantasy beyond 10 days.

It's impossible to forecast synoptic patterns 2 months out; but I'm sure something in there will be right out of pure coincidence. 

[iapennell]

Accuweather's winter forecast concurs with the seasonal prediction that I have posted above: They predict stormy conditions with snow on the northern hills at times for December until mid-January, then for high-pressure over Scandinavia to deliver wintry weather from the east during February (http://www.accuweather.com/). 

This does provide some encouragement that my understanding of macroscale and regional meteorological processes is on a sound footing. That said, no long-term forecast is totally infallible, but I have made what I believe (based on the information I have gathered) to be the correct call for the broad outline of how the Winter will play out.

Unlike recent winters, there is a good deal more in the global drivers to point to severe cold spells later in the season. This is not a prediction of a repeat of 2009/10 or 2010/11, just that there will be some wintry weather later in the winter. 

[John Badrick]

21 hours ago, hillbilly said:

I have to admire your passion in detail Ian but I am sceptical of any foreast beyond 2 weeks so much so I don' know wether to laugh or cry.However I wish you luck with your prediction and if it predicts correct we can all come and worship you.Personally I don' give predictions but with a string of mild winters we are due at least an average one or one cooler than of late.The maths says we have to have something cooler so it will probably be the mildest winter ever recorded.

well Ian, has probably been the most accurate with his forecasts than anyone else in the last couple of years and I've always said I'm looking forward to the day when he forecasts a cold winter. Not quite there yet but I believe he thinks from 2020 will be the beginning of the harsh winters again in this country( is this right Ian?) I always wait for him to give his forecast until I get excited or in the last couple of winters annoyed with the upcoming season. There is a hint of excitement from me this year for later in the season after reading your forecast. Keep up the good work Ian 

[chrisbell-nottheweatherman]

21 hours ago, hillbilly said:

I have to admire your passion in detail Ian but I am sceptical of any foreast beyond 2 weeks so much so I don' know wether to laugh or cry.However I wish you luck with your prediction and if it predicts correct we can all come and worship you.Personally I don' give predictions but with a string of mild winters we are due at least an average one or one cooler than of late.The maths says we have to have something cooler so it will probably be the mildest winter ever recorded.

In actual fact probability says no such thing.  This winter is no more likely to be cold than any of the previous mild ones.  What is improbable, or rather was improbable was a series of mild winters of the length we've had, but the chances of a mild winter now are the same as they've been for many years, obviously excluding the effects of global factors such as QBO.

Edited November 12, 2017 by chrisbell-nottheweatherman

[Daniel*]

Very eloquently written - well done! Your record is as good as anyone’s on here, as ever the proof is in the pudding. 

A nature’ chap seems to agree with your overall flavour for the winter, with snowy and icy conditions into the New Year, before that he sees it to be snow free for most. Most likely merely a confidence, I fail to see how you can draw anything from animal activity and lunar phases. 

https://www.google.co.uk/amp/metro.co.uk/2017/11/18/worst-snow-since-1991-according-to-man-who-reads-thousand-year-old-moon-charts-7089048/amp/

[BLAST FROM THE PAST]

Ian

 

superb read and has to be looked at as feasible and very balanced as last year you were having none of the cold.  A great read and loads of info to learn from.  

 

BFTP

[V for Very Cold]

Fascinating article and much food for thought - thank you for your efforts  

[iapennell]

Nick Finnis' article on "Thoughts for Winter 2017/18- A Colder Winter than Normal?" makes predictions for colder weather for the reasons that I have- Easterly QBO, La Nina and a Quiet Sun leading to weaker Westerlies affecting Britain.

However, I disagree with his assertion that a warmer than usual North Atlantic increases the chance of cold weather in Britain, not least for the reason that warmer waters around and (usually) upwind of Britain have a warming effect. The atmospheric temperature and pressure gradients between the North Atlantic and a frigid Arctic are INCREASED by anomalous North Atlantic warmth and more moisture from warmer oceans fuel deeper depressions - as does the enhanced temperature and pressure gradients between the Arctic and North Atlantic: This would encourage stronger Westerlies heading towards NW Europe.  This is my main basis for predicting that the first half of the coming Winter will be wet and stormy; the cold spells will be late January / February 2018!

[northwestsnow]

Met office seemingly going for the polar opposite of the Dec forecast at this juncture- generally cold and blocked patterns favoured , at least for the 1st week to 10 days

[damianslaw]

7 hours ago, northwestsnow said:

Met office seemingly going for the polar opposite of the Dec forecast at this juncture- generally cold and blocked patterns favoured , at least for the 1st week to 10 days

Yes reading between the lines Met Office forecast for Dec suggest colder denser polar air looks like gaining the upper hand against tropical maritime, the latter making a few glancing appearances only - and mainly in the south and west. Suggests to me strong atlantic ridging, and a deep trough anchoring down from the NW, pulling in cold N/NW airstreams, with the UK mainly on the colder side of the jet, trough aligned NW-SE. Not a deep freeze, but preety wintry for the north and east.

 

 

[lassie23]

Any thoughts on whether this cool spell will be a damp squib  iapennell, are you expected a return to stormy atlantic sourced weather for the rest of the month?

[iapennell]

@lassie23 My prediction for December is for stormy conditions, particularly across Scotland and Northern England, but with winds from the west rather than south-west and for colder sub-Arctic incursions getting into the mix in the North.

We have just had Storm Caroline that has brought very strong winds to Scotland and North West England. As this deep depression moved east towards Norway much colder (and strong) north-westerly winds have brought snow to parts of Scotland, North West England and, in particular, the Isle of Man (where roads have been rendered impassable and ferry services to the island from Heysham and Liverpool suspended).

I expect much of the same weather for the rest of December, probably stormier than what it has been like to date. Strong westerly winds will bring rain along with mild temperatures: Following the passage of depressions there will be further cold snaps with north-westerly winds bringing snow showers and night frosts (with snow more likely in Scotland and the North). 

There is, of course, another Arctic snap predicted for next weekend that will, in turn, be followed by milder Westerlies: However we do not have the sustained high-latitude blocking anticyclones that would bring severe and long-lasting cold at present. For that to occur you would need a strong anticyclone of 1040mb or more persisting over Scandinavia (or over Greenland and Iceland for northerlies) and remaining resolutely in place.

  I do remain confident that such high-pressure will set in over the European Arctic in late January and February: This is what will help to deliver our coldest and most severe wintry spells for five years. 

[Hocus Pocus]

Looks a bust already Ian unless we see a dramatic switch within the model output then the stormy mild spell will be put on hold for another month.

[Snowyowl9]

When was the last storm we had the red sun yellow sky storm ex hurricane back in oct.

The models seem to be showing an interesting ridge to scandi,anyway no storms yet across the bulk of the country november or this month bar northern Scotland Thursday.

[karyo]

On 12/9/2017 at 19:01, Hocus Pocus said:

Looks a bust already Ian unless we see a dramatic switch within the model output then the stormy mild spell will be put on hold for another month.

The first half of Dec was a bit wintrier than Ian's forecast was suggesting but there was a storm for the northern half of the country and now we are back to a more typical December pattern of mild and unsettled. I think he has done reasonably well so far.

My interest now is to see whether the January cold spell materialises.