Boundary Layer ModificationAdded : Friday at 12:30 Right, a full on meteorological discussion today so grab a coffee and settle in as we look at why Northwesterlies which we will see next week are a little more interesting than you may think. Don't worry though, we will try to explain the physics behind this as best we can for all.
It should come as no surprise now that next week we are expecting a real change to the weather across the UK as winds swing in from the Northwest, here is the chart for Monday :-
The "fetch" from this system is pretty impressive. You can see how the isobars run in a straight line from Southeast England right up to the Labrador Strait between Greenland and Canada. This isn't something which we usually see in synoptic charts, as usually there is some low pressure system coming out of Canada which cuts off the flow.
If you take a look at the upper air temperatures for the same period you can see this :-
That is some pretty darn cold air which is pooled up around the Labrador and it's heading Southeast towards us, but you need to remember that this air needs to travel around 2500 miles across the Atlantic Ocean. The Atlantic, whilst not the warmest ocean in the world, is still around 10-14c at the surface. This obviously warms up the air as it approaches from the source, but not all of it...
Now, this is where the physics happens... When the colder air runs over the warmer seas it will obviously modify the air near the surface, but the warmer sea destabilises the air at the surface and with colder air aloft the air continues to rise and develops into some impressive showers.
When this air rises and falls within the showers it "churns" up the atmosphere and takes warmer air higher and brings down colder air from aloft and because the sea remains the same temperature day/night we find this process continuing 24 hours a day.
If you take a look at the 2m temperature for Tuesday you can see the colder surface air here :-
But, if you check the 850hpa temperatures, you can see the colder air here :-
This is because the boundary layer in the bottom 100m or so will be warmer than the air aloft, but markedly so.
This means, that next week and you will see the forecasts for snow and ice away from coastal areas and inland, in particular above 100m or so due to the fact that the air nearer the surface has been modified by the Atlantic, whilst the air higher up far less so.
There you go, a crash course in boundary layer modification, but an impressive weather scenario nonetheless.
METEOROLOGIST : MARSH |