Welcome to my 15th consecutive European winter forecast. In this forecast, the conclusions drawn for the upcoming 90-day meteorological winter period will be based on current climate and climate drivers at play including current global SST profile, ENSO, Solar & much more!

An important factor to consider is the level of warmth in our oceans, atmosphere and on land. Record warmth continues to increase and this will most certainly shift the parameters, possibly altering the influences of the climate drivers we look at.

Current global sea surface temperature.

What we know…

• Warm oceans overall

• NEUTRAL to Weak La Nina

• Cold PDO (Pacific Decadal Oscillation)

• Warm AMO (Atlantic Multidecadal Oscillation)

• Neutral IOD (Indian Ocean Dipole)

• West QBO (Quasi-biennial Oscillation)

• Solar Maximum (25)

First let’s look at the Arctic Oscillation and North Atlantic Oscillation. These are probably our most important or most focused on of the several teleconnections we look at from a European winter pattern point of view.

Short and simple, these indexes are a measure of air pressure and the below graphics show what is a positive of both oscillations which tend to promote milder weather for Europe while a negative promotes, colder.

ARCTIC OSCILLATION

NORTH ATLANTIC OSCILLATION

Sometimes the above oscillations reflect one another while other times they go their separate ways. While the AO/NAO is important in determining a potentially colder or milder pattern, what drives these oscillations is even more important. Let’s take a tour of the bigger picture.

ENSO (El Nino Southern Oscillation Index)

For months now, all the talk has been La Nina.

AI Overview…

Back in spring the models were suggesting a strong cold phase of ENSO but due to other factors which shall be discussed below, in truth and as of late November we remain with neutral conditions. So, neither El or La.

Both El Nino and La Nina have significance on the global atmosphere. The stronger these warm or cold phases (strong to super), the greater and more overwhelming their influence. More often than not a strong to super El Nino or La Nina tends to have a milder outcome for Western Europe.

The neutral to possibly borderline weak La Nina (colder than normal SST’s in the equatorial Pacific) is one thing but WHERE is the coldest waters positioned within the Pacific along the equator? and is the cold waters affecting the atmosphere above?

This is measured by two key indexes, 1) SOI value or 2) MEI (multi-variant enso index). In short these values as of late November DON’T reflect a La Nina base state and with a warming of waters, we are struggling to see La Nina truly forming in the coming weeks.

Latest Southern Oscillation Index values

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Even if La Nina does develop and would be weak at that, it may well be too little to late to have any real winter influence.

That being said however, if waters happened to cool west of 80 W longitude (international dateline) this may have influence and I shall explain that further down.

All in all, in terms of ENSO as an indicator for a cold or warm winter, the jury is still out.

QBO (Quasi-biennial Oscillation)

NASA Description

The Quasi-biennial Oscillation (QBO) is a tropical, lower stratospheric, downward propagating zonal wind variation, with an average period of ~28 months. The importance of the QBO is that it dominates the variability of the tropical lower stratospheric meteorology [Wallace, 1973]. The QBO is also important for seasonal forecasting, and the QBO controls stratospheric ozone and water variability that can modulate surface ultra-violet (UV) and infrared (IR) radiation.

This winter will be a West QBO!

Put simply, WESTERLY winds within the stratosphere over the equator tends to favour both a stronger polar vortex and westerly flow (jet stream). Stronger the PV and JT the more likely of a +AO and usually +NAO leading to a milder, more Atlantic dominated outcome for Northwest Europe (stronger Icelandic low and Azores high).

EASTERLY winds tend to have frictional effects on the westerlies and this can result in a weaker PV resulting in a more wavy (amplified) jet allowing warmth northwards towards the pole and cold southwards towards lower latitudes (-AO/NAO).

It has to be said that it’s not that simple and the above isn’t always the case, other outside factors have been known to flip the above rule the opposite way.

Solar Maximum (Cycle 25)

AI Overview

One factor that has been know to flip the QBO rule the other way is solar activity, a maximum to be exact!

We’re currently at the solar maximum of cycle 25. Stronger than 24 but weaker than 23 as seen when looking at sunspot numbers below.

Some wording from Dr Joe D’Aleo.

When the sun is active, there are more geomagnetic storms and aurora events, there is less low clouds due to diffused cosmic rays, more UV (increasing 6 to 8%) which warms through ozone chemistry and a measurable increase in brightness. There is enhanced warming globally..

A quiet sun has lower geomagnetic warming, more low cloudiness over oceans which increases albedo (reflectivity) and lower UV (6 to 8%) which usually means a cold expanded polar vortex. Atmospheric flow patterns tend to be more amplified and persistent.

High solar can mean less blocking except when the QBO is westerly as it is now. The west QBO can mean episodes of a strat warming in the polar regions which allows polar air often trapped at higher latitudes to expand south. Snow is often less in most high flux years.

In short, solar maximum suggests stronger polar vortex and westerlies bottling arctic air over the pole, this flooding the mid latitudes with Atlantic air…

However, west QBO’s and solar max combo tends in increase probability for weaker polar vortex, greater chance for an SSW and -AO/NAO.

There is higher than usual levels of stratospheric ozone over the pole. This can be attributed to stronger incoming solar radiation.

Neutral IOD (Indian Ocean Dipole)

Without explaining much, the IOD is neutral courtesy of a largely warm anomaly across much of the basin and likely to stay that way for the foreseeable.

What’s been happening from TROPICS to POLE to Stratosphere (Sept through mid-Oct?)

Let’s now discuss probably an aspect or element of forecasting I’m most passionate and excited about and has proved me correct, even ahead of the models in recent months…

When warm vs cold SST anomalies throughout the tropics becomes important.

We cannot underestimate the power of the MJO (MADDEN JULIAN OSCILLATION). This has undoubtedly become an integral tool in my mid to long range forecasts and it works pretty well for the most part.

A seemingly simple rainfall/thunderstorm enhancing ‘atmospheric wave‘ propagating eastward through the equatorial Indian and Pacific Oceans releases heat north which can dictate the jet stream position, strength and amplitude therefore dictates the upstream and downstream wavelengths (ridges/troughs). It even dictates tropical cyclone productively globally as well as El Nino/La Nina.

The influence the tropics (MJO) have on the mid to high latitudes can then lead to impacts from troposphere into stratosphere.

Relationship between tropics and pole & effects on polar vortex

By driving an MJO induced phases 7-8-1 ‘high latitude blocking pattern’ (-AO/NAO), this forces ‘swelling of the troposphere’ and therefore can produce drag within the stratospheric circulation, leading to ‘waves of warming’ and consequential weakening of the polar vortex as a result.

Phases 2-3 into 4-5 can have the opposite effect. With lack of blocking due to lower heights within the arctic troposphere, strengthening of the polar vortex within the stratosphere occurs.

Here are the 8 phases of the MJO (enhanced convection and thunderstorm activity)

Warm & cold sea surface temperature anomalies can dictate WHERE the MJO’s ‘enhanced convection’ positions itself which therefore dictates a flat or zonal strong jet stream or weak and amplified mid latitude pattern, ultimately dictating a + or – AO/NAO.

What do these various phases correlate to?

Here’s where we’ve been in the past 90 days.

The correlation particularly between late August and late November with unsettled/stormy (phases 2-3), blocky high pressure (phases 5-6) and colder spells (phases 7-8-1) with positive & negative AO/NAO is uncanny to say the least.

The mild to cold swings have been accurately mapped out by myself since the end of summer.

As of late November, the late August to mid October pattern is repeating. Entering phase 2-3 then 4-5 (Indian Ocean to Indonesia), we had strong UPWARD motion IO/MC while strong SUBSIDENCE over cent/east Pacific.

Surface winds blowing eastwards across the Pacific helped cool equatorial Pacific and this provided a kick to the developing La Nina (& atmospheric response above, the SOI). We also saw a shut down in the tropical Atlantic due to large scale subsidence and also a RECORD STRONG +NAO.

Then came September and October and a shift in MJO into phases 7-8-1 (west to central Pacific) resulting in big swings in the Arctic/N Atlantic pressure pattern + to -AO/NAO.

The strong ‘atmospheric mountains’ generated by this eastward progression of thunderstorms within the tropics poking through the shallow ‘polar troposphere’ likely creates drag within the stratospheric circulation causing record weak mean zonal winds and SPV displacement (Sep into Oct). This is at a time when the vortex should be largely undisturbed and strengthening at a steady rate.

Strong positives near stationary blocks were observed over northern North America, Greenland and Ural Mountains, this likely aided a ‘trop to strat’ frictional warming of the stratospheric polar vortex, slowing it’s growth and displacing off the pole.

Spells of arctic source cold entered the mid latitudes in W Europe and central Asia. As MJO re-enters the Indian Ocean and slowly heads towards Indonesia (phase 4-5), the AO/NAO heads positive and milder oceanic influence returns to areas which observed ‘periods of cold’.

As MJO amplifies BACK INTO PHASES 3-4-5 during October, I don’t think there’s a coincidence between this, the lowering of high latitude heights (+AO/NAO) and the likely uptick in 10pha mean zonal wind speeds (strengthening of the polar vortex) during the 2nd half of October.

As the MJO passes through the IO late November, so the jet stream over the Atlantic tends to strengthen with a growing thermal gradient over E North America. Mild potential stormy first couple of weeks of December?

So, what’s happening within the stratospheric polar vortex? Looks to be strengthening into the start of winter. This would make sense if the MJO returns to the Indian Ocean and eventually maritime continent (phases 2-3, 4-5), +AO/NAO and lack of lower atmospheric blocking/resistance into the lower stratosphere. 

An active MJO over the Indian Ocean is likely to lead to some ‘minor displacement’ of the polar vortex and likely cross polar flow from Siberia to N America. Meaning arctic intrusions into Canada and US but this likely fires up the Atlantic jet which forces mild, unsettled weather into NW Europe.

THE 2024-25 WINTER VERDICT

I’m going with my gut and my gut is saying mild outdoes cold overall.

However, a mild December-February overall DOESN’T mean NO COLD. I suspect we could see a few wild swings between mild, perhaps very mild to cold.

The SST anomalies are one thing and stratosphere another. The uniform ‘warm Indian Ocean to Indonesia region’ suggests the MJO could get stuck in the stormier phases of 2 into 3 and mild 4-5 resulting in a predominantly +AO/NAO. MILD for NW Europe.

However, the recent weeks of westerly winds blowing over the west tropical Pacific could help move the MJO from Indian to Pacific and more importantly CENTRAL Pacific (phase 7-8-1) and therefore shifting the AO/NAO negative.

I believe we have some ‘decent periods of cold‘ as we should see periods with the MJO crossing the central Pacific (if waters DON’T cool much) but I think the winter default position will be 2-3 into 4-5 resulting in a lot of Atlantic dominance for NW Europe.

The polar vortex behavior is the elephant in the room for me. It’s expected strengthening into December aided by a lack of high latitude blocking (+AO/NAO) and MJO phase 2-3 into 4-5 isn’t a good indicator for anything other than mild, perhaps stormy at times through weeks 1-2, perhaps even 3 of December.

The graphic below shows the mean zonal winds at 10mb, strengthening through much of December, this supports the idea of low heights over the arctic (+AO) and less friction within the lower 50mb level of the stratosphere.

The MJO I think will head back towards 7-8 mid to late December which ‘may’ support a colder final 5 to 10 days of December.

One cannot rule out an SSW which would support a more prolonged and stronger period of cold weather.

There’s little evidence of any significant weakening of the polar vortex much before Christmas. The neutral ENSO-Solar Max-West QBO suggests a 50/50 chance for an SSW and without one, I believe MILD will be stronger and longer than any cold spells but the cold spells we do see, could be substantial with 2 or 3 amplified rotations through phases 7-8-1 like observed during the autumn just ending.

Monthly Breakdown

DECEMBER 2024

Mild with opportunity for a few named storms into W/NW Europe, colder with heavy snowfall into the Balkans and east Europe.

As MJO is expected to return towards phase 6 we could see another period of stagnant high pressure dominance which may result in a dry but perhaps chilly spell with linger fog etc mid month.

Late December offers an opportunity for something colder towards Christmas-New Year and a slightly higher chance for snow during the holidays!

SLIGHTLY MILDER THAN AVERAGE WESTERN EUROPE, COLDER EAST, SOUTHEAST EUROPE

JANUARY 2025

Depending on the behavior of the polar vortex and likely MJO return towards the Indian Ocean, I would say mild Atlantic conditions remain through the first 10-15 days of January with another opportunity for something colder through the final 10-15 days of the month.

AVERAGE, POSSIBLY SLIGHTLY BELOW AVERAGE OVERALL WITH SWINGS BETWEEN MILD AND COLD

FEBRUARY 2025

Again, a lot depends on the polar vortex but I think yet another month sees spells of both mild and cold perhaps stormy.

Potentially COLDER THAN AVERAGE

Milder than average winter overall

Latest from ECMWF

December 2024

January 2025

February 2025

December-February

Past years with neutral to La Nina conditions, Solar max & West QBO!

Recent solar max years 

Cycle 21: Dec 1979

Cycle 22: Nov 1989

Cycle 23: Nov 2001

Cycle 24: Apr 2014

Cycle 25: 2024**

Close matches between Solar max & developing La Nina’s (Jul-Sep)

1988 (year before solar max)

2000 (year before solar max)

Solar max 2014 occurred in between the dev Nina years of 2011 & 2016.

Combo of solar max + developing La Nina + west QBO years

La Niña     QBO     Solar Max or Near     Cool UK summer

1950
1951
1955
1956
1962
1971
1974
1976
1989            E                         MAX
1999            W
2000           W                       NR MAX                *
2008           W
2011             W                                                        *
2012            W-E                                                    *
2021             W
2022            W

2024            W                        MAX                       *

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