On the Horizon – Historic cold spell arrives

John gives us his latest thoughts on likely weather trends on the horizon over the next few weeks. To ensure you are reading the very latest weekly blog, check out Wow and Why

As I write this blog, we’re on the verge of entering one of the most impactful cold spells for many years. There now seems little doubt that there will be major impacts from a combination of extremely low temperatures and, for some, heavy snowfall.  But how long will this remarkable spell last into March?

I expect school closures, as well as major impacts on travel and other infrastructure

MONDAY 26TH FEBRUARY – SUNDAY 4TH MARCH

Severe impacts

By Monday, very cold (‘polar continental’) air will have arrived across all areas of the UK – a marked step up in chill from the weekend. Temperatures in many places will be barely above freezing, the cold accentuated by the easterly wind.

Weather-wise, initially, western areas will be driest and brightest. But already there will be snow flurries further east. And through the day, snow showers here will become heavy and more prolonged. Accumulating snowfall is likely to develop across central and eastern parts of the UK, especially as we head into the night.

By Tuesday. I’m expecting disruptive amounts of snowfall to have fallen in some places. There is likely to be marked variation in amounts of snowfall, but parts of southeast England, East Anglia, northeast England and eastern Scotland are in line for some of the larger accumulations.

Conditions will deteriorate further through the midweek period, with the prospect of disruptive snowfall to be carried more widely westwards across some parts of the UK. Nobody is immune to snowfall by this time. I expect school closures, as well as major impacts on travel and other infrastructure.

One feature of the snow is that it will be very dry and powdery, due to the intense cold. As a result, drifting of snow into deeper accumulations is likely.

The most intense cold is likely through this period. Many places will struggle to get above freezing by day, meaning melting of snow will be limited, despite the strengthening sunshine. Overnight frost will be severe and penetrating as a result of the easterly wind. Where winds fall light over snow-cover, double-figure negative temperatures are possible.

We’ll need reminding that we’re into early March as the bitter cold continues to the end of the week. But there are some interesting variations between computer models in other respects. Some attempt to push low pressure systems up from the south, whilst others usher in fronts from the north. The jury is still out. However, either way, the nett result will be to inject moisture into the pre-existing cold airmass resident across the UK. And that brings the prospect of a spell of more prolonged heavy snowfall – either from the south or the north – by next weekend.

The jet stream will be left weak and ‘punch drunk’ for some considerable time

MONDAY 5TH MARCH – SUNDAY 11TH MARCH

Lingering cold and snow

The hemispheric reversal of winds, initiated in the stratosphere in mid-February, will have a lingering effect on weather systems well into March. The jet stream will be left weak and ‘punch drunk’ for some considerable time. As a result, milder Atlantic air will struggle to dislodge the cold.

Milder air may make some limited inroads into some southern and western parts of the UK, turning some of the snow to rain.

But on balance, the week will remain chilly for most, with the prospect of further sleet and snow, especially the further north and east we are across the UK. Overnight frosts will remain quite widespread.

 

MONDAY 12TH MARCH – SUNDAY 25TH MARCH

A slow recovery

It’s hard to believe, given the cold weather that we will still be enduring, that we are approaching the equinox.

Given the increasing strength of the sun, temperatures, almost inevitably, will be rising from their nadir at the start of the month.

But the recovery into something that could be called “springlike” looks like being slow and erratic. I expect further wintry weather at times, with temperatures remaining lower than normal for the time of year.

For weather historians, March 2013 stands out in recent memory as a remarkably cold month – the coldest for over 50 years. As now, the severely cold weather then was preceded by a Sudden Stratospheric Warming. So the question is whether we are about to endure something of a repeat performance…

Given the current volatility of the atmosphere, we will, of course, update this blog during the week if our thoughts change significantly in the days ahead.