Active vs InactiveAdded : Monday at 14:30 You probably hear us using the term active front or an inactive front in some of our discussions. When you think of inactive you probably imagine your other half lazing on the sofa on a Sunday evening with a tub of ice cream watching a box set. But, frontal systems are a little different.
This is the front coming on on Wednesday :-
You can see the rather heavy rain from this cold front across Southwest, Central and Northeast England as the green echo in the rainband.
This is an active cold front. It should come as no surprise that an active front means that there is some decent activity on it, in this case heavy rain. But, the term has a little more of a meaning to meteorologists as to define a front as active or inactive we tend to look at the upper air temperatures.
This is the 850mb temperatures for the same time for the UK on Wednesday afternoon :-
You can clearly see the temperature drop at upper levels either side of the front, it's actually around a 10c different. But notice too the "Z" pattern where the front comes through in the isobars. This will indicate a sharp drop in pressure as the front comes through before it kicks back up and rises. The reason? Well, the pressure drops because of rising air through the front and then rises as the colder, more dense air behind the front moves in.
If you take a look at the surface temperature charts you can see a similar temperature drop as the front comes through :-
So, an active frontal system coming through across the UK on Wednesday afternoon and into Wednesday evening with some heavy rain embedded through the front, but at least you now know why when we call a front active we mean expect some activity within the front thanks to a decent temperature difference either side of it.
METEOROLOGIST : MARSH |