Todays Squall FrontAdded : Wednesday at 13:30 A bit of a closer look at the squall line which came across much of the UK today and also how it tied in Storm Helene (DWD)/Georgina (UKMO).
First up the radar :-
You can see the cold front across much of Central, Southwest and into Eastern parts of England. This is the surface cold front, in fact, you can see the boundary to the colder air where the front is orange/yellow from Cornwall up to the Midlands.
Ahead of this though is a narrow line (across Southern England, London and into East Anglia) which is a squall.
These features are perfectly common along cold fronts where you get two contrasting airmasses either side of the main front. During the Summer these tend to bring things like thunderstorms, shelf clouds and if you see one in the desert or dusty areas then they lift the dust up ahead of them (you know the sort of Armageddon pictures you see from Australia/Iraq etc)
The models handled it pretty well, this is the AROME model :-
You can see the temperature difference of a few degrees either side of the squall too :-
A squall line is basically natures big broom. As the colder air pushes East, so it forces the warmer air ahead of it to rise quickly. The air condenses and this brings the heavy rainfall. The winds though are part and parcel of this process. As the air is lifted quickly, it has to drag in surface air ahead of it in order to balance out the vacuum. This is the gusty and strong winds which appear ahead of the front, in fact, when you get gusts of wind ahead of a squall you can be pretty sure than in 5 minutes that air will have been drawn into the squall and sent up to 35,000ft!
If you look at the pressure charts for the squall :-
Can you see the tell tale "Z" pattern? This is the model telling us that the squall is active as it draws in air and forces it to rise (that will cause your barometer to drop quickly) and then colder air comes in from the West and the air which ascended in the squall descends on the other side (that will cause your barometer to kick up quickly)
Squall lines are natures way of telling you that it doesn't like that imbalance of colder and warmer air and has to do something about it.
If you got caught in it then you probably aren't too impressed. But that's what a squall line is and you have to admit they are pretty impressive.
METEOROLOGIST : MARSH |