Met Office chart puzzle

[jack.h...@gmail.com]

Potentially the most useful Map & chart, precipitation from: https://www.metoffice.gov.uk/

Screen grab

Maybe someone can explain the pink colours indicating hail.  I am confused as whenever there is ANY precipitation this chart ALWAYS seems to show widespread 'hail'.  I had (mis?)understood that hail is associated only with deep convection and as such is usually quite localised.

PS.  Just started snowing again (not hail !) at 0900.

Jack

[Graham Easterling]

I'm obviously a long way from northern Scotland, but the majority of showers over the sea in a cold sector like this normally contain hail, even off Cornwall. Any snow is restricted to away from windward coasts, with the rare exception (like yesterday). It doesn't appear to need deep convection, any old Cb will do.

It's rather the exception for showers not to contain hail. As a result winter months  dominated by cold sector Atlantic air can contain 10 or more days with hail. December 2020 was the last such month here in Penzance.

Hail in winter is far, far more common here than it was in during my Wootton Bassett period. 

Graham

Penzance

[Freddie]

Hail requires vigorous convection, rather than deep - although the depth does help in the summer.

[Len]

'Hail requires vigorous convection, rather than deep'

Not sure what you mean by deep here.

At what height does it need to be before it can be called deep?

The Valentia tephigram here shows Cb tops possible to 400 hPA or about 22000ft.

There are plenty of them in view atm from Wembury giving rain mixed with hail showers. Temp 4C, dew 0C.

Had a sprinkling of snow at 0600 GMT when temp was 1C.

Len

Wembury

SW Devon coast

[jack.h...@gmail.com]

I was not so much talking about how hail forms but the fact that there is much pink on these charts.  It would have suggested that I have had almost continuous hail storms over the past few days.  Yes, plenty of snow showers but not a hint of hail.  Maybe at altitude it was hail.   But surely these charts are supposed to be for ground level?

That is why I find this particular Met Office chart very odd.

Jack

[Len W]

It is possible that the algorithm used to distinguish between rain, hail, and snow is not as good as it is made out to be.

The radar echo difference between hail and snow must be rather small.

Len

Wembury

[Graham Easterling]

A few light showers here today, all of which contained hail even the the clouds appeared to have limited vertical extent, with the exception of 1 which had a clear anvil. Total rainfall <1mm

Graham