Metoffice updated warning . Nothing special but highlights the uncertainty
Rain or sleet is likely to fall onto frozen ground to bring a risk of ice on untreated surfaces on Saturday morning. In addition, some transient snow is possible, mainly above 200 metres where 1 cm may settle for a time very locally. This is an update to the warning since some wet snow has already fallen across parts of the Midlands and may lead to icy surfaces on Friday evening - hence this area is now included and the start time has been brought forward. Please be aware of the potential for difficult driving conditions and slippery surfaces.
Clear skies on Friday evening will allow temperatures to fall widely below freezing. Later in the night a frontal band will move in from the northwest bringing a mixture of rain, sleet, and perhaps some transient snow - the snow mostly on high ground, with a centimetre perhaps settling on the Cotswolds and Chilterns for a time - also across parts of the Midlands on Friday evening. However, the main hazard is likely to be ice formation where rain or sleet falls onto sub-zero surfaces, or washes off earlier road treatment. The risk of ice will occur earliest across the northwest of the yellow area before reducing by dawn - by this time the risk will transfer further southeast, although there is some uncertainty as to how quickly this will occur and it is possible that precipitation may not reach the far southeast of England until mid morning when the road temperatures will have risen above freezing.