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Well here we go again, winter 2021/22 is here, and many of you are eager to know how this winter may shape up to be.



The forecast headlines are:

Overall, temperatures are forecast to be colder than average expecting the coldest winter in UK since 2012/13
January expected to be the coldest month, however, coldest weather could happen later in winter, after mid month, possibly SSW induced and extend into February, potential for notably low temperatures with significant wintry hazards
50-60% likely to be a wetter than average Winter drier in the east
December forecast to be the wettest month

First, I will examine the main global climate drivers of winter 2021/22 of which when are in different amplitudes/phases can give a broad idea of how winter will turn out.


ENSO (El Nino Southern Oscillation)


This autumn we have seen La Nina conditions redevelop this is associated with cooler than normal sea surface temperatures (SSTs) in central and eastern Pacific. Nina conditions are expected to last through entirety of winter 2021/22. This is second winter in row with La Nina conditions we saw the ENSO go neutral in spring and this lasted through summer.

During La Nina, the easterly trade winds are stronger this means significant upwelling of deeper and cooler subsurface waters, to ocean surface, therefore, we see central and eastern tropical Pacific Ocean become colder than normal.


What we see is the strength of La Nina/El Nino affects the position and strength of jet stream the atmospheric changes in North Pacific in turn influences the weather in North America, and the altered jet stream continues onwards across North Atlantic and Europe in like a connected chain. A ripple thousands of miles away in North Pacific can have a large impact on the type of weather we see. During La Nina we often see an Aleutian ridge a big area of high pressure off western North America in North Pacific, this often causes North Pacific jet stream to bend sharply S/SE across North America. Often La Nina winters are colder and snowier in Canada.


The wavy jet continues as it exits east coast of US across North Atlantic and to Europe, and notably this meridional theme is more frequent with weak La Nina conditions, and coldest anomalies are in eastern Pacific we often see Atlantic ridging a blocking area of high pressure to west of British Isles. The mobile westerlies are gone and this encourages colder northerly or easterly winds. Interestingly we begin December 2021 with weak La Nina conditions and also the coldest anomalies are increasingly focused more in east. This means chance of cold snaps in early winter are rather high in Europe.


A strong La Nina favours a strong jet stream this is associated with +NAO (North Atlantic Oscillation), winters which are dominated by this are often very mild and unsettled winters. Indeed in last decade we have seen many of them. It is advisable to never take a broad brush approach with forecasting every winter is unique, indeed in 2010/11 winter which UK experienced its coldest December since 1890 the La Nina was strong although coldest anomalies were in eastern Pacific, which could have been crucial.


The 2010/11 winter although burnt out very quickly, which likely was due to strong nature of La Nina, but again highlights regardless of strength of La Nina we tend to see increased chance of cold weather patterns earlier in winter. This winter we could see further strengthening but likely no more than moderate. As such the second half of winter could have a higher chance of cold spells than the traditional La Nina which coldest anomalies are fairly evenly distributed west to east, and the further we head into winter the unsettled westerlies gather in strength.

In summary I find ENSO encouraging and to be highly influential this winter but uncertainty lays is how much strengthening of La Nina we see over winter, La Nina becoming strong while unlikely would increase probability of a mild and wet late winter.


The Quasi Biennial Oscillation (QBO)

This sounds complicated doesn't it? Essentially in a very simple way it refers to winds blowing above equator every 14 months or so, these winds can completely change direction from westerly to easterly or vice versa. This winter we will be in easterly phase of QBO and again the last time it was during 2017/18 winter. Notice the links which are being made with that winter? Which was also a La Nina winter. During easterly phase of QBO we tend to see increased risk of disruption to polar vortex, which slows down jet stream increasing risk of cold weather outbreaks. We are not only seeing easterly but a strong one, while sample size is not huge since 1950s we have never had a winter which was mild with deeply descended easterlies. Thanks Marco! Overall, this year QBO is particularly favourable to a cold winter and to a higher chance of polar vortex disruption, and I anticipate will be highly influential.


Stratosphere

Now onto the stratospheric polar vortex (SPV) which also feeds into previously discussed QBO, very important in determining winter prospects, this is is a huge area of very cold, low pressure which forms in autumn with return of polar night, it spins anticlockwise at North Pole in December-January it reaches peak strength.


The stratospheric circulation is higher in atmosphere above the troposphere, the troposphere is where the weather happens, what we see with stronger stratosphere polar vortex (SPV) is like paint dripping down a wall the enhanced westerlies high in atmosphere propagate down into troposphere and we see a strong tropospheric polar vortex (TPV). This, therefore, accelerates the speed of the jet stream a strong jet stream is likely to bring lots of low pressure, wet and windy weather at our latitude.



So knowing the state of polar vortex is very useful tool unfortunately predictability is rather low beyond week 2, hence, occasionally seasonal models can go epically wrong, disruption to these upper westerlies can totally radically change weather patterns across Northern Hemisphere to be more conducive to wintery outbreaks. This was exhibited in February 2021 and perhaps more famously in February 2018 which were a result of Sudden Stratospheric Warning (SSW) and featured a split - these serve like a sharp pin popping a balloon, significant cold is unleashed from higher latitudes but not everywhere can see this extreme cold.


This winter we begin with a stronger than average SPV, this is not positive for cold weather patterns in mid latitudes, if this is to continue a wetter and milder winter would be favoured with a ++ Arctic Oscillation (AO) trapping cold in North Pole, however, what we've seen so far these strong westerlies have failed to really descend and influence our weather patterns. You will have observed how dry November has been.

In recent days we've seen a sign of a disturbance in the force with Dr Cohen well on the case, the signalling of Ural Blocking was also seen last winter this helped result in SSW in January 2021, and weeks later in February we experienced some very cold easterlies albeit not as dramatic as 3 years earlier.


The signalling for this atmospheric "road block" earlier in mid December is interesting, as this could weaken the polar vortex and increase risk of a significant cold spell in January the coldest month of winter. The strong easterly phase of QBO this winter in tandem with La Nina also enhances risk of disruption to polar vortex and cold weather patterns in Europe, therefore, I believe the probability of an "attack" is quite high this winter.

Solar Cycle

This is a one which the science does not agree upon, nonetheless I am an observer and advocate. I noticed the increased northern blocking patterns and wavy jet stream after 2008 solar minimum, and again following late 2019 solar minimum our weather patterns have become more 'unstable' oscillating between v wet and dry. We are no longer in solar minimum but it is believed the ascending part is where we tend to see lag effects, interestingly this December will be 2 years since solar minimum. December 2010 was also 2 years following 2008 solar minimum and activity is very similar, it might be a tenuous link but an interesting one.



Northern Hemisphere snow cover and Arctic ice

Snow coverage across NE Europe is more extensive than this time last year, the Scandinavia region is also significantly colder. Sweden in recent days has witnessed its lowest November temperature since 1980. This thickening snowpack and rapid fall in temperatures means northeasterly winds are likely to be unusually severely cold for so early in winter.


Current Eurasian snow cover

Eurasian snow cover 26th November 2010


The Eurasian snow cover we see it closely resemble late November 2010, also we observe uncanny similarity with Arctic sea ice, in fact as of 28/11/2021 we have over 400,000 square km more ice. This is reflected by a colder Arctic of which I have mused over this autumn. Last winter we greatly struggled with having sufficiently cold air, the patterns were favourable with good air flows but they did not live up to expectations. Winter 2021/22 likely for this to be less problematic, and thus could make a major difference in marginal snow situations.


North Atlantic Sea Surface Temperatures

The North Atlantic at present is warm, however, lately with chilly northwesterly winds this has caused SSTs to drop closer to normal NW of British Isles, meaning Polar Maritime northwesterly winds will not be particularly modified. The subtropical Atlantic is particularly warm this has contributed to some of exceptionally mild conditions this autumn, any southwesterly flows this winter are likely to be very mild across Europe.


In winters 2009/10 and 2010/11 the Atlantic SST anomalies were quite favourable we had a tripole pattern, this is when you have cold waters sandwiched between warmer waters to the north and south. This winter we do not have this, but I theorise the widespread above normal SSTs could be ironically beneficial, temperature gradients fuel the jet stream and associated wet and stormy weather. The North Sea is also comfortably above average this may make easterly winds less cold, however, if we see bitterly cold Siberian winds there would be vigorous convection, frequent heavy snow showers in east/southeast. Overall with SSTs there are good and bad aspects I don't anticipate Atlantic SSTs to be particularly influential.



Seasonal models


In last 15 years particularly we have seen great advancements in long range seasonal modelling most of models UKMO, ECMWF and Meteo-France are going for a milder than average winter +NAO. It is worth noting a three month mean can mask an awful amount of variation for instance one cold winter month against two much milder months the cold anomaly is completely lost, being a country which does not typically experience prolonged cold/snow they must be used carefully.


UKMO's Glosea depicts a mild winter with dreaded Euro high, the jet stream is kept to north of UK allowing for a dry winter with an unusual lack of winter storms.



French seasonal model is likewise going for an above average winter, but increased mobility of Atlantic westerlies a wet winter in this case, which also might lessen the mild feel.


The European model by far most compelling for a cold winter signal, average temperatures are favoured overall, there is also evidence of a high latitude blocking signal Scandinavia is shown warmer than average which possibly suggests an anticyclone. This encourages cold easterly flows into Europe. What is more stark is strength of the warmer signal between Iceland and Svalbard, I believe this suggests a strong northern blocking signal, blocking here historically has resulted in some rather extreme and protracted cold winter conditions.


Typically I give a monthly breakdown but I do not think this is sensible, no one on this planet could give you a 100% roadmap of how this winter will evolve particularly this one.



In summary, as earlier mentioned the headlines are;

  • Overall, temperatures are forecast to be colder than average expecting the coldest winter in UK since 2012/13

  • January expected to be the coldest month, however, coldest weather could happen later in winter, after mid month, possibly SSW induced and extend into February, potential for notably low temperatures with significant wintry hazards

  • 50-60% likely to be a wetter than average Winter drier in the east

  • December forecast to be the wettest month


This is the first winter forecast I have gone for a colder than average winter, I am not super bullish it will be cold, so I am taking a calculated risk the benefits I suppose of not having clients, but this winter will likely go one of two ways. Despair or jubilation. Very wet and Atlantic driven or the blocking wins out and cold if very cold weather dominates. I hope that wasn't too wordy, I look forward to sharing more with you @TheSnowDreamer


P.s. If you are appreciative and have a little to spare, contributions to keep site up and running are greatly appreciated, many thanks


https://paypal.me/thesnowdreamer?country.x=GB&locale.x=en_GB


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Monday has began more characteristic of a hot midsummer day particularly across SE England. Heathrow Airport hitting 28.6C making it the hottest day of the year in UK.


However, elsewhere there has been a weakening cold front moving slowly southeastwards which has brought much cooler and cloudier conditions. This cold front will clear through SE tonight so the night will be less warm and humid. Tuesday is expected to be less hot, with highs at best of 25C with high pressure fully in control it will remain dry with plentiful sunny spells across many areas. Although, an approaching frontal system from west will bring cloud, wind and rain to N. Ireland and western and northern parts of Scotland in afternoon.



On Wednesday things become interesting a band of rain stalls across parts of Scotland and NW England during morning and dissipates (not that). We see the upper trough in Atlantic essentially an area of low pressure positioned to our northwest being forced and elongated south near Iberian peninsula, by the dome of high pressure in Europe. This helps pull in winds from a southerly direction introducing increasingly hot and humid air.



With abundant sunshine across eastern, central, and southern England temperatures will respond with 30C quite likely to be seen in London area.



But later in the day we see increasing instability generated by hot plume and into overnight Thursday we see a thundery low develop in northern France, this will drift north and is likely to bring an area of heavy rain and thunderstorms moving northeast across most of England and perhaps east of Wales most likely into early hours of Thursday.


These storms could contain prolific lightning, biblical rainfall, large hail and strong convective gusts I expect London, SE and East Anglia to have greatest risk of thundery action further west I expect less of a thundery nature more noted for their rainfall.


The humid and warm feel will continue through Thursday across eastern England with potential further thundery rain and elsewhere much fresher with decent sunny spells there could also be some showers most missing them.



On Friday further thundery rain is looking to advance northeast out of France once more largely across SE and East Anglia most areas staying dry and sunny, temperatures returning closer to average for the time of year.


Set to turn more unsettled next weekend, again we see low pressure moving north across France towards SE England the better day Saturday with possible early rain, Sunday a potentially larger area of rain which could impact much of the day.


Some welcome rain is to come following dry weather in recent weeks but perhaps some excessive amounts in places and increased risk of flash flooding owing to 'baked' dry soils. The second half of June is expected to be less settled and perhaps less warm but I anticipate a recovery, overall this June promises to be a solid summer month.

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Meteorological summer is here, and attention is increasingly drawn to what the weather is doing; in a time of limited foreign travel, the weather the UK experiences this summer will be of particular interest. In this blog post I will explore how this season could be shaping up, some summer thoughts are also given to wider European region in introductory section.



This summer offers at the very least to be a reasonable summer, summers such as 2007 which happened to be a particularly poor summer, could be well flagged, in contrast to this summer we are transitioning to neutral ENSO, instead of La Nina (cold ENSO) which these conditions developed in autumn 2020 and have now faded in spring 2021.


La Nina is associated with cooler equatorial Pacific waters this tends to affect global jet streams they meander more and there more extremes, for NW Europe where UK is positioned, this often means we sit on cool/unsettled side of jet stream with Atlantic blocking.


This is what characterised 2007-2012 summers La Nina was highly influential on their unsavoury note. Ideally El Nino (warm ENSO) is best teleconnection for long, warm and settled periods across Europe given we have not long moved from La Nina, it is probable we are still seeing feedbacks between the cooler oceans and atmosphere. And, therefore it would be unwise to assume this summer will be a long hot summer, the interaction of much cooler Atlantic air may trigger intense downpours and violent thunderstorms.


This summer I'm expecting the most anomalous heat to be located across southern Europe with blistering heat surging from North Africa with temperatures exceeding 40C in Spain, Portugal, Italy and possibly the south of France. It is possible this extreme heat might nudge further north and affect more of Northern Europe including UK, however, while I'm expecting Europe to have a warm summer. The slight mobility in North Atlantic region might just be enough to ensure hottest conditions are kept further east. Furthermore, ensuring hot weather is not as prolonged unlikely to be as fortunate across European continent.




QBO (Quasi-Biennial Oscillation)


Is essentially the term we use to describe stratospheric winds around the equator. There are two phases either westerly or easterly in a 9-18 month cycle. What we tend to see is during strong positive/westerly, we see increased westerly flow across Atlantic.


This summer we are entering the summer neutral, May's QBO number comes out as +0.31 therefore one would expect June's update to show a negative value. It is possible by winter it could be in strong easterly phase so that is of interest to winter junkies but none of that now. The transition to easterly phase of QBO this summer is largely good news, on negative side of things the positive is that extensive Arctic blocking which featured significantly and resulted in UK's coldest April since 1989 and coldest May since 1996 has subsided. The danger with eQBO this can help solidify these blocking regimes at these high latitudes, so it is reassuring the Arctic weather patterns has changed. Nonetheless, this may change and reemerge this would be more likely during La Nina summers and as previously stated it has faded.



North Atlantic Sea Surface Temperatures (SSTs)


SSTs in proximity of UK have warmed albeit they are only a bit above average +0.4C around Ireland they are cooler than average, approximately by -0.5C. In May 2018 SSTs were very elevated within UK coastal waters and this helped influence the extent of high temperatures. We similarly had a cold blob in North Atlantic but this one is further east 'aimed' at British Isles. Where waters are warmer this increases risk of high pressure formation, and therefore these cooler waters just positioned to our west might be less good news. Particularly for those further west which could be at more risk of Atlantic incursions. Indeed, this is a reason why I'm anticipating this to be a thundery summer where we see significant clashes of air masses.


Waters in tropical Atlantic are cooler than normal this is main development zone for tropical cyclones which can develop into hurricanes, we don't see them but they do tend to recurve up eastern seaboard and hitch a ride on jet stream bringing disturbed weather to UK. I am personally not expecting an active hurricane season which runs from August to October, therefore. late summer could be less threatened by the remnants of these hurricanes.



ENSO


I will not go into much detail here as I have discussed 'simply' before most models in IRI/CPC plume predict a continuation of ENSO neutral conditions throughout the summer. This indicates there's unlikely to be a major shake up in summer pattern, while indeed we could at times see cooler and wetter conditions this will not persist for long. The neutralisation of La Nina during spring has been very helpful in that respect.



Lastly looking at seasonal models the ECMWF model SEA55 has changed quite considerably from May update, instead of ridging (high pressure) being focused in North Atlantic this is common in La Nina regimes. In June update we see main ridging extend across all of Europe which has potential to bring very warm and dry conditions across region. The mean flow is coming from Azores so an unpleasant summer of high humidity and rising temperatures could be on cards. There are hints of Atlantic troughing (low pressure) with Greenland having a cooler summer, this may mean NW airstreams could be rather cool. Overall best conditions expected further south and east as is the norm and the greater risk of wetter and cooler conditions further north and west.



Summer Forecast Breakdown



Temperatures


Quite bullish on a warm summer potentially very warm for SE England, for areas further north and west the summer might be closer to average with less desirable weather while areas further south and east might escape. I consider a cool summer very unlikely <10%.


70% chance of a warmer than average summer

20% chance of an average summer

10% chance of cooler than average summer


Precipitation


This is very challenging to ascertain firstly a washout summer is not expected (sorry Jack Reeves), overall a drier summer is more likely than a wet summer intense and short lasting downpours, however, have the ability of really changing things but it must be emphasised of the large local variation. From a statistical pov a wet summer might not necessarily feel like it has been wet. Driest conditions are expected in SE with wettest conditions in far NW where the weather will take a more changeable flow through much of summer. I'm anticipating the driest month could well be June and this might be shared across country.


June


The month has began well with high pressure in total control, there is no indication that a major change will occur in next 1-2 weeks, in fact the modelling is growing increasingly confident of hot conditions developing later this week, which I do anticipate first 30C will be met this weekend. The second half of June it is probable things will be shaken up, there could well be limited success from westerlies, and high pressure and warmth rules all the way through. I am expecting June to be driest month of summer, I also think temps will be well above average potentially by more than +2C which is quite significant. I do not think we will see hottest weather of summer but very warm weather will be regularly occurring.


July


Confidence truly plummets, I can see early in month featuring some less desirable weather and nowhere would escape from cooler and wetter conditions. Overall, expecting July to be less abnormally warm compared to June, nonetheless, I think we will see hottest weather of summer and temperatures may exceed 35C. Continental Europe could be subject to very fierce and persistent heat and this might bring great suffering to vulnerable groups. I anticipate this summer month will be the most thundery with potential for severe storms.


August


We're sort of guessing at this point there has been a strange regularity to August's failing to impress in 21st century the 1990s were a particularly good decade (in more ways than one), we have not managed similar consistent highs since. Will this August offer something spectacular? Probably not, but, compared to last summer Nina conditions began developing in August this allowed the 2nd half of month to really deteriorated following on from intense heat earlier in month. Broadly expecting August to be a good summer month more traditional, rainfall closer to normal, June likely dry and July could vary extremely from dry to very wet.



So there we go that is my summer forecast for 2021, it offers to be an exciting season in my opinion to keep up with latest developments follow my tweets @TheSnowDreamer



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