Busted Forecasts And CapsAdded : Tuesday at 14:30 The warm spell comes to an end today and usually, we expect to see some thundery activity as this happens, but it's not always as clear cut as you might imagine.
Take a look at AROME for this afternoon :-
You can see how it progs heavy showers developing across parts of the East Midlands and East Anglia. But take look at FMI :-
Nothing! The reason is down to the AROME model forecasting the CAP to break across parts of Central and Eastern England later this afternoon.
The CAP is basically the inversion which is currently around 1500ft up in the atmosphere and stops the warm thermals from the ground rising in the atmosphere by having a layer of air warmer than its surroundings which means the air bubble starts to fall again.
When cold fronts come in from the West we find the air backing to a more Westerly direction at height and cooler air coming in aloft. This process erodes the CAP and allows the thermals to rise creating showers.
The first sign of this happening is if you see altocumulus castellenus clouds at around 8,000ft today. This means that the CAP is being eroded and mid level instability is developing.
The reason why AROME is going for this is due to the microscale temperature forecasts for the model. Check out the forecast temperatures at 2pm :-
You can see the ultra high resolution of the models picking out small towns and villages where thermal triggers are possible.
It's this granularity which allows the AROME to suggest that there is the potential for low level temperatures to be high enough for the CAP to be broken.
But of course models aren't always right... We are currently monitoring the temperatures across England in relation to what AROME is forecasting in order to gauge whether AROME will get it right or whether it will be a busted forecast.
METEOROLOGIST : MARSH |