Winter 2025/26 - General Discussion

Things are looking a little more interesting now. I haven't spoken about teleconnections much if any since the massive failure that was winter 2023-24 as that was the last straw which suggested to me that a lot of the things people look at no longer apply in a warming world. That may still be the case but today and it is towards the outer reaches of the model run, the GEFS this morning has begun to show a wave-2 pattern in the upper stratosphere later in November into December 2025. This could succeed possibly the earliest major sudden stratospheric warming on record in the final week of November. There have been only two major SSWs on record in the month of November back in 1958 and 1968.

What these wavenumbers basically mean is they tell you how many anticyclones and troughs are within a full latitude circle. In the case of wave-2, this means there are two anticyclones (high pressure) and two troughs (low pressure) in the northern hemispheric circle. A wave-2 pattern is typically characterised by a split of the polar vortex which keeps cold air bubbled in the arctic circle from filtering down to the lower latitudes normally. A wave-1 pattern where there is one anticyclone and one trough is normally associated with a displacement of the polar vortex from its normal position. A wave-2 pattern is more conducive to blocked, cold setups in western Europe than the former. More often than not they do lead to such but not 100% of the time. It is said that just over 2/3 of general sudden stratospheric warmings lead to cold, blocked setups - this includes the wave-1 events. Then of course once we do get the blocking, there's no guarantee that it would be in a position favourable for western Europe. Greenland highs for instance in recent years have often been west based whereby they've been too far west over towards Canada allowing any undercutting low pressure systems to bring milder, wet conditions to Ireland.

An early major SSW isn't necessarily a brilliant sign for cold, blocked setups because nocturnal cooling is at peak through mid-December to mid-January so unless there is a continued disturbance to the PV through favourable patterns, it is very likely that the PV aloft will rebound fairly swiftly. That does not mean it would correspond back to the tropospheric patterns as you can get disconnections. A safer bet would be to have a consistently weak vortex rather than one big knockout just to have it bounce back.

The one consistent red flag with modern winters that continues to be the case is sea surface temperatures are still above to well above average in our vicinity. There is a slight signature for a tripole in the North Atlantic of warm-cold-warm (which according to the UK Met Office has favoured negative North Atlantic Oscillation conditions historically) but it is not strong and therefore unlikely to be of much difference.

Warmer seas can give beefier showers with more moisture available to draw from but if the airmass is not sufficiently cold in the first place, showers will primarily fall as cold rain.

For this reason, it'd be foolish to expect a colder than average winter. In fact you'd expect a lot of mild conditions with cold airmasses moderated heavily. This does not discount sudden cold snaps that could provide surprises however.

We say the same basically every winter but the rollercoaster is active and here we go.