Welcome to my 11th annual winter forecast for Europe. In this forecast, the conclusions drawn for the upcoming 90-day meteorological winter period are based on current oceanic and atmospheric drivers and my understanding of their potential influence they may have.

Of course, pinpointing any specific pattern several weeks or months ahead is near impossible but we can provide potential trends and likelihoods.

There are a few ‘stand out’ factors or players that should almost certainly make winter 2020-21 quite different to 2019-20 which was very mild for not just the UK but Europe and much of the hemisphere.

Moderate to Strong La Nina

As seen in the below SSTA chart, the current and already mature La Nina stands out.

The most important aspect to the La Nina is that this SHOULD have a cooling influence globally. However, that cool down appears to be delayed, perhaps denied by continued warmth in several if not many areas of the world. I can only hope that this La Nina has the ability to turn down earth’s climatic thermostat.

Traditionally but not always, 1st year La Nina’s tend to bring the worst of ‘winter weather’ early in the season with milder 2nd halves.

During particularly strong La Nina’s, Eastern North America and Western Europe tend to be mild while colder over Western North America and Eurasia.

North Pacific warm pool is back… but?

Over the last 3 months, the waters have continued to cool across most of the equatorial Pacific while waters in the North Pacific, particularly south of Alaska, have warmed. This has proven to be quite unfavorable for North Atlantic/Greenland blocking and cold over Western Europe.

However, if you compare the above SST chart from Nov 12th vs Nov 25th below, there appears to be some cooling showing up along the south coast of Alaska thanks to a strong jet stream and storminess over the region. Along with other factors discussed below, I hope that warm pool has less of a downstream influence over the Atlantic and hemisphere.

Indian Ocean Dipole (IOD), Madden Julian Oscillation (MJO) & Stratospheric Polar Vortex (PV)

During September and October, as the sun’s angle and strength lowered and now remains below the horizon, so a new tropospheric and stratospheric polar vortex was born. It indeed strengthened fast during autumn 2020 and had the hallmarks of a 2019-20 repeat. In fact, for early to mid November, it pushed record strong and cold levels.

As a result, autumn was warm and wet for the UK and Western Europe with a firmly +AO/NAO. So much so that it was the 2nd highest positive AO for November in the last 70 years.

However, the when you look at the Indian Ocean Dipole this autumn compared to last, it’s very different and the MJO too is in a different position. These two aspects straight away make this year very different to last. While strong in early November, the polar vortex has been weakening as we enter December.

As can be seen in the below chart, while the IOD rocketed to record positive during autumn 2019, the same period this year has been slightly negative and that is having a very different feedback to the atmosphere.

The positive IOD and MJO stuck in phases 6 and 7 last autumn and winter is likely one of the greatest contributors to the polar vortex remaining strong throughout last winter. The lack of attack from the tropics led to a cold north, warm south and strong jet stream driving warm air from Pacific and Atlantic across the continents.

This time around, we haven’t the strong positive IOD or MJO stuck in phases 6 and 7. This time it’s rotating through phases 8, 1, 2, 3 and 4, focusing enhanced convection and thunderstorm activity from Africa across the Indian Ocean to the Maritime continent.

Thunderstorms going off over the east Indian Ocean is releasing heat north and enhancing the Siberian high.

Both the heat release from MJO vertically and northwards and stronger Siberian high both create friction to the polar vortex, particularly the tropospheric PV but stratosphere too.

Modelling sees the continuation of weaker zonal winds at 10hpa (upper stratosphere) well into winter.

So what does that mean? Weaker zonal winds circling the PV make for a weaker jet stream at 40,000ft and a more vulnerable PV. Open to attack in the form of stretching, displacement and even the occurrence of a sudden stratospheric warming event. The more fluid MJO this year should have greater influence on the PV and there is greater chance of warm pools from the low to mid latitudes penetrating north into the high latitudes (high latitude blocking) forcing polar air into the mid latitudes.

Quasi-Biennial Oscillation (QBO)

What’s the QBO? The QBO are winds which blow either easterly or westerly within the stratosphere above the equator. It’s safe to say that the QBO is currently and likely to remain in a westerly phase through at least the first half of winter 2020-21.

Why’s that important? The current westerly QBO was supposed to flip easterly and that flip failed and so on the face of it, a westerly QBO goes against the grain when it comes to ‘weak PV’s’ and chance for a sudden stratospheric warming event (SSWE). A westerly QBO (winds blowing west to east within the stratosphere) tends to maintain a stronger than normal polar vortex. In essence, a strong PV and westerly QBO combined tends to make it much harder for high latitude blocking to develop.

However, despite the westerly QBO, we have a weak and likely to remain, weak PV which should help increase chances for blocking and the southward discharge of polar air.

Sudden Stratospheric Warming (SSW)

A favourable IOD, MJO, QBO can all have down or upstream contribution to an eventual full-scale sudden stratospheric warming event. The last SSWE occurred in February 2018 which led to the infamous ‘Beast from the East’.

Since winter 2017-18, the PV has been too strong to support any such repeat in 2019 or 2020.

Predicting a SSWE months or even weeks in advance is very difficult. However, the oceanic, tropospheric and stratospheric conditions seen this year could arguably favour another SSWE in early 2021.

The GFS sees several attacks on the vortex at 10hpa on the Asia-Pacific side over the next couple of weeks.

Arctic Oscillation (AO) & North Atlantic Oscillation (NAO)

As you can see from the below AO/NAO charts which go back to 1950, since our last major cold winter (late 2010), the overall trend has been positive for both AO/NAO. Hence the lack of cold winters. One can blame solar cycles, warmer ocean, global warming. I think it’s probably also true to say that we’re overdue another -AO/NAO winter.

AO

NAO

That remains to be seen but certainly looking in the short term, it’s looking interesting, especially with the PV expected to remain weaker than average.

Solar Minimum

Before I discuss my 2020-21 forecast, I want to touch on the solar cycle as NASA declared the commencement of cycle 25 at the close of 2019, start of 2020.

When looking back to the end of the 21st century’s first decade, we ended cycle 23 and began cycle 24. Prior to the most recent solar minimum, the last occurred in 2008 and was followed, coincidentally or not, by the worst back to back spells of winter for the UK and Western Europe since 1978-79.

The big test comes either this winter or even more so next, whether the weaker solar cycles of modern times really do provide cooling influence on our climate the way some in the scientific community believe. I truly believed the the 2009-10 and first part of 2010-11 happened as a direct consequence to the solar minimum. But that being said, despite have supposedly the weakest sun in 200 years, why is our planet continuing to warm.

We are back to the same solar state/cycle/minimum as we close 2020 as we were in December 2009. Let’s see what this winter brings as solar minimums are meant to increase -AO/NAO’s, SSWE’s and harsher winters. We observed a record -AO/NAO during winter 2009-10. Solar minimum induced? If so, you’d expect another strong -AO/NAO this year or next.

In fairness to the solar minimum theory, the 2-3 winters prior to the previous minimum were some of our warmest and stormiest (2006-07, 2007-08 and 2008-09) like last year.

Trouble is, our oceans are considerably warmer and consequently our atmosphere now than during the previous solar minimum.

If the winters of the next 2-3 years fail to produce at least something resembling 1978-79 or indeed 2009-10, well I would throw that theory out the window.

IF YOU LOOK AT THE BELOW LONG RANGE MODELS, IT’S NOT GOOD VIEWING IF YOU WISH FOR COLD!

CFSv2 FORECAST FOR DECEMBER-FEBRUARY 2020-21

700mb height anomaly

2-metre temperature anomaly

MET OFFICE FORECAST FOR DECEMBER-FEBRUARY 2020-21

500mb height anomaly

Mean sea level pressure

2m temperature anomaly

JAMSTEC FORECAST FOR DECEMBER-FEBRUARY 2020-21

Surface air temperature

Precipitation anomaly

Mark Vogan’s 2020-21 Winter Prediction For Europe

Based on all points discussed above, this winter should almost definitely prove colder than 2019-20 for Europe. There’s a much greater potential for spells featuring high latitude blocking, especially over the Arctic (-AO). So polar air should get involved to a much greater degree with the mid latitude pattern. As for the NAO, we could see more back and forth between positive, neutral and negative.

DECEMBER 2020

Based on the current -AO/NAO as we entered December’s opening week, it looks like the month overall should average at or slightly below average for the UK, France, Iberia and possibly into central parts of Europe. Warmer than average for much of Scandinavia and Eastern Europe from Italy, Greece and Turkey.

There’s enough high latitude blocking extending from Scandinavia and Ural Mountains to force polar air south but the Atlantic isn’t shutting down so cold and unsettled/stormy is likely to dominate.

December 2020 2m temperature anomaly for Europe so far!

CFSv2 weeklies show a strong ridge extending from Scandinavia up into the arctic. This should feed cold continental air westwards towards the UK. However, the Atlantic will attempt to keep firing lows east towards the UK and so we have an atmospheric fight on the cards. Who wins, remains to be seen.

Run-Up to Christmas/New Year?

As you can see above, the model hold on to the Scandinavian block through the festive period. One thing worth noting is see the ridge on the North American east coast? notice the model has it hooking up with the Scandinavia block over Greenland. This shuts off the northwest Atlantic and suggests we’re likely to see more cold continental rather than mild oceanic air if this evolves… Cold, perhaps snowy run-up to Christmas is very much on the table!!!

So, an interesting and cold December is expected.

JANUARY 2021

What for it… bang!

CFSv2 monthly goes straight to a textbook +AO/NAO January.

Could this happen? Yes, in fact I do see a return to a +AO/NAO around Christmas or New Year which brings the return of milder weather either at New Year or into the 1st week of January. This could herald a fairly unexciting first 15-20 days of January with perhaps folks declaring winter over.

BUT, I expect a 2nd -AO/NAO spell, perhaps due to a mid to late January split or collapse of the PV (SSWE). If this occurs and in the right place then we could see the return to significantly cold, snowy end to January, beginning of February.

FEBRUARY 2021

A true SSWE or not, I believe we continue with frequent spells of cold through much of February.

When looking at the CFSv2 monthly, it’s as if I’ve drawn the 500mb chart. Yes, a cold February.

Overall, I believe winter 2020-21 will have similarity to some of the interesting, even exciting back and forth winters of the 1990s as well as 2013-14 and 2017-18.

There is certainly potential for some memorable cold and snowy spells this year but we could see just as many mild spells which makes the 90-day meteorological winter ‘warmer-than-average.

Tags: featured, winter forecast 2020-21