Dave Cornwell wrote:

Hi Will, I don't know if you remember many years ago sending me a
little
simple rule of thumb for estimating the different probabilities of
snow risk, based on adding the DP and temp together. Well I've used it
ever since and it has proved to be very accurate on many occasions,
today being one such.
I realise there are other more sophisticated factors, evaporative
cooling etc. but it has nevertheless proved extremely useful
Thanks,
Dave

I'm intrigued now Dave .. share it with us all please.