European Winter Outlook 2020-21

Hello, I am going to analyse the key climate drivers and derive a forecast for the European meterological winter that has just arrived.

Model Outlook

This isn’t going to weigh heavily in the final analysis, but for reference here is the multi model ensemble provided by Copernicus.

For Europe, we see ridging dominating, reducing snowfall for much of the continent. And we also see a +NAO more Atlantic driven forecast for the season in the UK.

Sunspots

SILSO data/image, Royal Observatory of Belgium, Brussels

Same as the last few outlooks, basically we are still in a solar minimum, which in theory helps a negative Arctic Oscillation. This would therefore assist snowfall in Southern Europe and the UK, but I don’t weigh sunspots highly as a tool in winter seasonal prediction.

QBO

We are looking at a descending positive/westerly QBO, that tends to have an effect at avoiding stratospheric warmings. And as we can see a certain effect on the European climate:

The general effects shown by the analog on the right:

  • Greenland high and Atlantic trough, and therefore a rough -NAO setup in the Atlantic.
  • But this has left in its wake a European ridge.
  • This may bring an active Atlantic for the UK, possibly some cold spells, but largely a maritime influence.
  • And of course warmer and drier for much of Europe, the best falls for the Alps based on this towards the West.

Our specific ENSO and QBO analog shows:

  • +NAO and a positive Arctic Oscillation
  • Dry and warm for much of Central and Southern Europe.
  • Possibly wet for the UK.

So overall not very good for snowfall for either the UK or Europe.

ENSO

We are heading into a Moderate Nina for this winter, with us expected to be at the depths of this Nina in the next month or so.

We are in the midst of an east-based La Niña that is stretching throughout the ENSO basin, but still focused on the Eastern end of the Pacific.

Our humble moderate Nina (east-based to basinwide) analog shows:

  • Scandinavian/Barents-Kara ridging dominance.
  • A mild-moderate ridge pattern for SE Europe.
  • A sort of -NAO set-up with Azores troughing
  • Less precipitation/snowfall for Turkey.
  • More snowfall for Southern Alps
  • Less Precip for UK/Northern Alps/Northern Europe.
  • Colder for Eastern Europe.

Stratosphere

I see an average to slightly above average chance for a SSW, most likely in January:

  1. A descending westerly or positive QBO will weaken chances for the development of Sudden Stratospheric Warming events.
  2. Brewer Dobson Circulation is stronger than normal in both of the NH and SH subtropics as well as over the tropics this month. I expect a stronger than normal BDC over the winter. This increases ozone in the SPV during the winter, which increases the chance of a SSW.
  3. Average Siberian Snow Cover does not really affect the stratosphere, but the low Barents-Kara Sea Ice does improve chances for a SSW.
  4. Solar minimum is still taking place at this point, favouring a -AO and potential stratospheric disruption.
  5. December’s +EAMTs and amplified pattern could help to amplify a stratospheric disruption down the road.

Taking a look at the modelling for the stratosphere this season, January looks like the most interesting month for potential stratospheric disruptions on both EC and UKMO, with EC the more enthusiastic option.

Sea Ice

The NASA GMAO forecast for around Christmas is for lower than average sea ice in the Barents-Kara Sea Ice region, which is more likely to induce a -AO/-NAO and to help to disturb the stratospheric vortex.

Snow Cover

October in terms of the expansion of the Siberian snow cover was pretty average with a pretty neutral impact. Late October and Early November brought a slump of the expansion, which may have had a negative impact down the line on the potential extratropical cooling effect and setting up of SSWs.

November saw a large increase of snowfall extent across Eurasia, and the resulting impact of that has been the strengthening of the Siberian High. This helps to increase pressure on the stratospheric polar vortex.

Although October wasn’t very exciting in Siberia, November shows some hope for a colder winter for the UK and Southern Europe/Alps, with potentially a more -AO/-NAO outlook focused on the potential for a SSW.

MJO


Here we have the expected tropical wave pattern for the winter ahead, that focuses on a Phase 2-3 (Dec) to phase 4/5/6 (Feb) approach to the winter, with a slow shift of focus from the Eastern Indian Ocean as the focus of tropical activity, to the Maritime Continent.

Phase 3 MJO + 10 days promotes a +NAO (good for Northern Alps snowfall, bad for Southern Alps/Europe and UK) and Phase 6 MJO + 10 days promotes a -NAO (basically the reverse). So we see a stronger favouring of –

Late October/November have featured a far more positive AAM/amplified pattern, which makes things more interesting with the potential for SSWs and disruption to the polar vortex.

It has also delivered good results for snowfall for the UK and the Southern Alps in the short-medium term, which could prove good if it continues.

Atlantic

This is probably a setup that favours a +NAO in the North Atlantic, with cold SSTAs south of Greenland amplifying a trough, and tight temperature bars from the North American continent that helps to amplify the North Atlantic jetstream.

On the other hand, colder SSTs west of the British Isles may help bring a colder outlook for the UK and the continent at large.

Conclusions

Call it the optimist in me, but this current December amplification event has got me more interested in a colder winter for Europe. The GWO has made it clear that it is at least for December more interested in the potential to see a counter to the oceanic Nina state.

It is important to make it clear that just because we have a Nina in the oceans, this does not necessarily have to translate to the atmosphere.

Given the first half of December is quite possibly going to be focused on a -NAO with positive effects for the UK and Southern Europe, we could see a counter to this over Christmas and New Years.

But I am interested in the prospect of a SSW later in the winter probably in January with its impacts felt in February. So perhaps a more +NAO look moving into January, and another change up possible if the impacts of the SSW propagate to the troposphere.

But these conflicting conditions have certainly made this one a hard for me, and I personally am feeling greatly confident. On the other hand, I have again produced a vague map showing my basic thoughts for this winter.

  • For the UK, an average to slightly above average snow season focused in a colder December and February. A less favourable more maritime pattern in January, with a +NAO, a weaker winter if it remains in control.
  • Southern Alps to get an average to slightly above average season.
  • Northern Alps to receive an average to slightly above average season, focused towards the middle of winter.
  • Eastern Europe is likely to receive average to below average snowfall, but a strong proliferation of the -NAO due to the +AAM or a possible SSW may help out particularly in the SE.

I know that a number of the drivers, particularly QBO and the Atlantic opposes this look. But the potential fluidity of the tropical and extratropical state and possibility for stratospheric disruption shows me at least that it won’t be a entirely awful season for Europe. Whether it bears much fruit is only for time to tell.

Thanks so much for reading. 

Seasonal outlooks tend to have bias and errors, due to the fact that these forecasts are so far out. So don’t use these outlooks to make important decisions. These outlooks is meant to be interesting information, that can help to see what the season would be like. 

This was a complex one, so I appreciate the support for the blog!

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