As you may have heard on the news, Feb 2021 got underway in dramatic fashion over in Northeast USA.
A major snowstorm, putting down 1-2 feet of snow across a wide area, has led to widespread power outages and disruption to infrastructure.
Parts of the UK are also seeing a snowy start to the month – not in such dramatic fashion, but still enough for the Met Office to issue severe weather warnings, including an amber warning for the higher ground of the northern Pennines, where up to 15 cm of snow is forecast on Tue 2nd.
The snow risk becomes largely confined to Scotland for 3rd-4th but is expected to return southward at the weekend.
In fact, this marks the onset of a week that brings a high risk of severe winter weather to many parts of northern Europe.
Severe Winter Weather – Big Snowstorms?
Not necessarily. Depending on where you are in Europe, the term can refer to as little as a few centimetres of accumulating snow. It depends on how readily the transport network can be disrupted.
On this occasion, though, the risks include dangerously cold conditions, widespread ice formation and yes, the possibility of snowstorms.
This is especially concerning when the transport network is crucial for combatting an epidemic – both for rolling out vaccines and treating those who have contracted the virus.
That comes on top of the usual disruption to industry, such as delayed or cancelled deliveries and outdoor labour.
Such impacts are only partially offset by the benefits of an overall shift toward working from home in response to lockdown restrictions. Yet even this can be undermined if the power goes out.
Europe’s Frozen Northeast
As I type this, the northeast of Europe, especially Scandinavia, is freezing cold. All of it – a wide swathe of below zero °C daily mean temperatures. In places well below – most notably in Norway and Sweden.
It’s not abnormal for this to happen at times in the winter months. What is abnormal is for that very cold air to be transported westward, to visit countries such as the UK and France.
You see, there’s usually an airflow from the Atlantic which blocks such movement. Periodically, it tends to push the cold away east, toward Russia.
This weekend, though, the prognosis is different: The Atlantic flow is expected to be diverted toward southwest Europe. This is brought about by high pressure to the north of the UK, in fact across much of the Arctic.
That has strong links to the lagged impact of a sudden stratospheric warming that took place last month. Back then I wrote about the increased probability of cold air in 2nd half Jan and on into Feb.
Sur enough, January’s seen numerous snow events in parts of northern Europe – more than usual for places such as the UK – and now we have strong signs that February may up the ante.
Beast from the East? It Depends…
With the Atlantic flow diverted south, the door is open for an easterly flow to bring that very cold air across northern-central and north-western parts of Europe by the end of the weekend.
With that comes a high risk of disruptive snowfall. The chart below is one of many scenarios for how this may look as of midday Sunday. Please note that the position of snow (pink shading) could vary by hundreds of miles from what you see here.
Forecast model chart produced by MetDesk, using ECMWF model output data, and hosted by wxcharts.com
To the east of England, a powerful frontal system is expected to develop. To the south will be unusually warm air for the time of year, to the north very cold air.
Forecast models suggest that during the following days, this boundary will waver north and south but perhaps not by very much. All the while, producing snowfall, heavy at times. Accumulations in the effected (land!) areas could exceed 20 cm widely and reach double that in places.
I must again stress the uncertainty over the positioning, though: 100s of miles around what’s shown!
In that area, this could be a very severe event, arguably worthy of the ‘Beast from the East’ title in.
To the west of there, the details are (even) more uncertain.
The ‘Beast’ is Less Sure About the UK
These two countries look to be within the western fringes of the main ‘surge’ of cold air from the east, at least as we begin the week of 8th Feb.
Signs are snowfall here may be largely ‘convective’ in nature. This means it comes from clouds developing in an unstable environment to the point that they produce snow.
When very cold air crosses the North Sea, a big temperature gradient occurs between the sea (usually 4-6°C in Feb) and the air around a kilometre above it (say, -8 to -12°C).
This setup supports strong uplift of moist air parcels through the atmosphere. That’s the prime ingredient for developing shower clouds.
This occurs most strongly over the sea, but the showers can travel inland on the wind. The chart shown earlier illustrates this. It shows snow showers making it up to 100 miles inland across southeast England.
We should bear in mind, though, that forecast models tend to ‘dry out’ shower clouds too fast in this setup. Typically, they reach at least twice the distance inland that they predict.
Generally, this setup tends to produce large accumulations (at least 10 cm; severe) for many eastern parts of England, with amounts increasingly light the further west you go, down to 0-5 cm in western parts.
For the upcoming spell, there’s uncertainty over just how far west the very cold air aloft makes it. On the other hand, the air pressure looks low enough in the south that the air may not need to be as cold as usual for snow showers to sustain well inland. Worth staying tuned to my updates @peacockreports!
Before moving on, I must mention an alternative outcome that has a low but not insignificant chance. It involves the frontal snow setting up further west or northwest, such that parts of the UK are impacted by it. This could bring larger snowfall amounts to England BUT also raises the possibility that warmer air crosses the southeast, at least for a short time. That would bring heavy rain rather than snow.
Could the Severe Weather Last the Whole Week?
As of midday 2nd February, the predominant signal from the forecast models is for the severe setup to be more than fleeting. We’re talking until at least Wed 10th in the northwest, Fri 12th in the central-north.
Shown below is an ensemble mean forecast departure of temperatures from average at the 850 mb pressure level, midnight Wed 10th. That’s just over 1 km elevation but is a good indicator of what sort of airmasses are driving the surface weather conditions.
Forecast model chart produced and hosted by tropicaltidbits.com, using ECMWF model output data.
For northern Europe, this is about as cold an ensemble mean as you could expect to see at over a week’s range from the forecast initialisation.
Looking later in the week, confidence inevitably drops away. There’s a strong suggestion that low pressure systems will attempt to sweep the cold air away east, but it’s not clear how quickly.
In fact, against such cold airmasses, the first attempt tends to struggle or fail completely. As systems battle to advance, heavy frontal snowfall can occur along the cold-mild boundary.
So, even as the very cold air arrives this weekend, we’ll be needing to keep an eye on what may happen later the following week. It’s going to be a very busy time for weather forecasters in northern Europe!
The impetus is there stay aware and be prepared for what might be.
James Peacock MSc
Head Meteorologist at MetSwift