FORECASTERS were forced to admit today that they don't know how much snow is likely to fall tomorrow, or where.

But they emphasis that clearing skies on Thursday night will bring an increased risk of ice.

The Met Office yesterday issued a yellow 'be aware' warning for snow valid from 10am on Thursday until 9pm.

This has now been extended to just before midnight on Thursday but ice now seems to be a greater hazard for Wiltshire and Swindon than snow.

In a yellow 'be aware' warning the Met Office says: "Rain moving eastwards across the south of the UK on Thursday may turn to snow in places.

"There is a chance of snow settling with disruption to road, rail and air services as well as interruptions to power supplies and other utilities - this more likely across East Anglia and southeast England. Associated heavy rain and strong winds may prove additional hazards.

"As skies clear on Thursday night there is also potential for widespread ice to form quite rapidly on untreated surfaces.

"This is an update to slightly increase the risk of disruption from snow, as well as to introduce ice as a hazard."

The chief forecaster said: "As a developing area of low pressure moves east across southern Britain on Thursday there is potential for rain to turn rapidly to snow as cold air is drawn in.

"However, there is a great deal of uncertainty over the track and intensity of this system, meaning that confidence is low in the amount and extent of any snow."

And chief meteorologist Paul Gundersen said conditions will become increasingly cold and windy as polar air spreads south across the country.

He said: "Wintry showers are also likely to affect many areas, most likely falling as snow over higher ground but occasionally also to low ground, especially where showers occur inland overnight.

"On Thursday a band of rain spreading from the west across southern parts is likely to turn wintry during the afternoon, with the potential for heavy snow in places.

"As this clears through the evening, with clear skies there is a risk of a widespread frost and icy conditions quickly forming."

Public Health England is urging people to take action to keep themselves and others warm and well over the coming days.

Director for health protection, Professor Paul Cosford, said: "Think now about what you need to do to prepare: if you need vital medicine or food get it before the bad weather arrives.

"People with underlying health conditions, very young children and those aged over 65 are at greatest risk, so think what you can do to help others."

Local authority areas affected by the warning include Wiltshire, Swindon, Bath and North East Somerset, Bristol, Devon, Dorset, Gloucestershire, North Somerset, Somerset and South Gloucestershire.