Time For Something CoolerAdded : Thursday at 13:55 You know how when you are full up and someone talks about having a sticky toffee desert just makes you feel ill? Well, today, instead of talking about the heat, we will talk about something a little cooler...
Before that though and we are monitoring the risk of thunderstorms across parts of Northern England later today. One interesting feature of thunderstorms is hail. It's obviously formed by ice crystals going up and down within the cloud, but how do we know how big they will be?
The answer, is that we use a model variable called updraft helicity. This tells us how quickly the air is rising within the potential storm cloud and this in turn can tell us roughly how large hail can kept aloft before becoming too large.
Obviously, there are other factors to take into consideration such as weight-to-drag ratio, but as a rough guide, here are the vertical wind speeds vs hail size we use :-
Pea (0.5cm) 15 MPH
Penny (2.5cm) 35 MPH
Golfball (4.5cm) 50 MPH
Baseball (6.5cm) 80 MPH
The vertical velocity of any storms developing across Northern areas today could be around 20-40mph which explains why we have gone for moderate size hail being possible, but as we said, there are a few other variables which is why it's never used as a golden rule.
Back to cooler things and here is the forecast chart for Saturday :-
You can see the warmer air now up across Scandinavia and cooler air coming in from the West across the British Isles. The warmer air gets caught up to the North of the UK into next week which results in a rather clumsy breakdown to cooler conditions and low pressure across Southern areas :-
So, not your classic breakdown, but cooler, fresher conditions for all in time for the weekend. Typical eh?
METEOROLOGIST : MARSH |