If this comes off, it will be an extremely impressive call by the Met Office - it was five days out when they issued the advisory! My personal opinion is that we will see some sleet and transient wet snow at low levels (in Cheltenham), with accumulations on the hills, from around 150m. However as TC's post illustrated it's such a complex situation (thanks for the post btw), and I think forecasters are right to be warning of snow because the potential is there!