High pressure has dominated the weather so far this November and has brought most of us plenty of anticyclonic gloom. A warm, moist tropical maritime air mass penetrated the high pressure system and has resulted in a persistent layer of stratocumulus, often with some light drizzle, haze and/or high pollution trapped near the surface as well. The main exceptions have been northern and eastern Scotland, due to the winds in Scotland having been predominantly southerly or south-westerly, allowing some sunshine to come through in the lee of high ground.
This is finally set to change for Monday, as while we will maintain high pressure, we will see a clearer, colder polar maritime air mass come into the high pressure area, and the high will become centred to the west of Britain, producing northerly winds.
The northerlies will not be particularly cold for the time of year, because they will not be pulling air in from very far north. This means that Monday is likely to be a sunny day for most of the country. However, cloudier weather is expected to develop again through Tuesday and Wednesday as we will see another warm and moist tropical maritime air mass come in, rotating around the northern flank of the high pressure and heading southwards through Britain.
It is looking probable that the high pressure will lose its dominance by around 16 November, with more unsettled weather taking over after that. However, this will mean that high pressure will have dominated the weather throughout the first half of November for most of the country, which is highly unusual, especially at this time of year. In the past 50 years or so, it has been common for the first week of November to be anticyclonic, but rarely has the high pressure area stuck around beyond the first week.
Potential for northerlies around the 18th-21st
As the high pressure area continues to move away to the west, there is potential for this to open the door for colder northerlies to head in from the Arctic. With it being upwards of a week out, there is plenty of uncertainty over this: while it does look probable that Arctic air will push southwards around north-western Europe, it is unclear how much cold air will push south, and it is unclear whether this will directly hit the British Isles or predominantly go out to the west or east.
Long range guidance, e.g. from the ECMWF long range model and from the demise of El Nino in the Pacific and a possible switch to a La Nina event, points towards a mild, changeable, westerly dominated winter upcoming. However, as Nick Finnis noted in a recent preliminary Winter forecast update, it is quite common for Decembers in such years to have a high frequency of north-westerly winds, before west to south-westerlies become more dominant later in the winter. The current progression is consistent with this: during the transition from high pressure to a mild and changeable westerly type, we will see high pressure centred in the mid-North Atlantic for a time which will result in a period when there will be potential for some northerlies. It is also quite a common pattern for mid to late November.
Some notes on mid to late November snowfalls
Until the 2000s, snow at low levels in the second half of November was fairly common, particularly in the north, although in most cases it didn’t stick around on the ground for long at low levels. This pattern with high pressure to the west and northerly blasts has historically been the most common source of November snowfalls. However, occasionally we have also seen substantial “easterly” snowfalls in the second half of November, and when they have cropped up they have sometimes produced significant falls and a lasting snow cover, such as in 2010 and 1993.
With the recent climatic warming trend, recent November northerlies have had a greater tendency to deliver rain and sleet at low levels rather than snow, but snow remains possible. Some parts of the country had falling and lying snow to sea level as recently as the last few days of November 2023, and there was another example near the end of November 2021. The last time snow fell widely on low ground just after mid-November was in 2015, via a northerly blast in an otherwise mild and wet month, between the 20th and 22nd.
It is also worth noting that some November northerlies end up delivering cold, dry and sunny weather for the majority of the UK, with wintry showers largely confined to north and east-facing coasts. Typically to get more widespread wintry precipitation requires there to be troughs in the northerly flow, frontal systems pushing against the cold air, or winds switching to more of a north-easterly or north-westerly direction at times bringing showers further inland.
At present the extent of any northerly outbreaks in mid to late November 2024 is still uncertain, but medium range forecast model outputs increasingly point towards a substantial chance of us seeing one or two northerly outbreaks between now and the end of November.
