Could the current stratospheric warming lead to cold and snow?
There has been a lot of hype about the current Stratospheric warming, but you will notice there is a common theme in many of these forecasts… they only show the charts from the upper stratosphere showing the strong warming and reversal of the normal winds.
A lot of the forecasters fail to understand or explain the physical dynamics and potential effects of this warming with the presumption of a stratospheric warming at the very top of the atmosphere will lead to cold weather at ground level.
If you want to read our analysis on the current warming please skip to the bottom of the page, or feel free to read on if you would like to learn a little more about stratospheric warmings.
The Stratosphere is many many miles above ground level and can often indirectly effect the weather conditions at the ground. So lets break the Stratosphere up into 2 layers, upper-middle and middle-lower (there are many more layers but we shall do this for simplicity).
One of the measurements of air pressure is hectopascals with the pressure of 1hpa (hectopascal) at the top of the atmosphere and averaging around 1000hpa at ground level which means as you head up through the atmosphere you can work out how high up you are by measuring the air pressure.
The upper and middle stratosphere is currently going through a major warming.
This warming has broken up the normal stable anti-clockwise circulation of the winds around the pole and has instead split the circulation into two pieces or two separate low pressure cells. You can see the wind direction from the small arrows on the isobars (lines). One piece is over the eastern USA and the other is over western Europe with a high pressure cell (clockwise winds) out towards NW Alaska.
As time goes on the upper stratosphere maintains this type of wind pattern and even 10 days later the situation remains much the same
You can see that over the UK we are in a flow from the North to Northeast which would be super cold if it was at ground level but we have to remember that this is at 10hpa or around 18 miles up.
As we move down through the atmosphere the effects of the warming become less pronounced, so here we can see the effect at 50hpa (approx 12 miles up) and you can see that the pattern resembles the 10hph chart to an extent.
There are a few significant differences though. Firstly the two circulations (low pressure cells) are a little more linked up. Also you can see that the high pressure cell that was visible further up in the atmosphere is no longer visible at this height, and finally you will see that the flow is a little more from the west.
So how will this affect the lower atmosphere closer to sea level here in southern England?
Nothing is ever 100% in predicting weather but it would seem most likely that high pressure may try to develop at sea level close to Greenland (below the slack area of the two circulations at 50hpa) and this may extend itself out into the Atlantic ocean at times. We would most likely see the effects of this as we move towards the middle and second half of the month.
We are fairly confident that a spell of NW to NE winds will develop on and off for a few weeks, bringing frosts and the potential of snow in places, although a northerly flow for us down here on the IoW is often a lot drier than an easterly flow (like we experienced in February and March 2018).
However, moisture can still become embedded in the flow leading to short spells of snow in a northerly wind. It doesn’t look very likely we will see a sustained cold spell but more likely that we will see short cold snaps from the north interspersed with slightly milder winds from the Atlantic.
Beyond this into February is still a little uncertain but it seems likely that a mixture of milder and colder spells will continue, although there is a lot that can happen between now and then but we will of course keep you updated.
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