[F]requent and heavy snow showers are expected on Wednesday and Thursday leading to some significant accumulations developing.
Long delays and cancellations on bus, rail and air travel could occur.
Roads may become blocked by deep snow, with many stranded vehicles and passengers.
Some rural communities might be cut off for several days. Long interruptions to power supplies and other services such as telephone and mobile phone networks, could occur.
Andy Page, Chief Meteorologist with the Met Office, said: “Snow showers already affecting the area will become heavier and more prolonged later on Wednesday and through the overnight period. 5cm of snow could fall within an hour in places and lying snow could reach 20-30 cm or possibly 40cm in a few places by mid morning on Thursday. Strong easterly winds will lead to significant drifting of lying snow”
“By Thursday morning, parts of England and Wales are forecast to see a more widespread area of snow associated with Storm Emma. This snow will likely become heavy through the afternoon across parts of southwest England and Wales, allowing 10-20cm of snow to accumulate quite widely here.
“Parts of south west England and Wales could also see freezing rain for a time on Thursday night – a relatively rare weather phenomena in the UK. This can result in a high level of impact as ice forms very rapidly on surfaces, leading to severe risks affecting transport and power networks.”
Dr Thomas Waite, of Public Health England’s Extreme Events team, said: “When the wind drives temperatures even lower, the risks to health can increase as even people not normally at risk from cold related illness can feel the effects more. This is why it’s so critical to keep warm; a good way is to keep homes heated to at least 18C.
“In weather like this our bodies have to work harder, older people, young children and those with long term conditions like heart and lung diseases, can really struggle to cope in such low temperatures. So do keep an eye on those at risk, wear several thin layers instead of fewer thicker ones and if you’re able, consider clearing paths of snow and ice. Staying warm will help you stay well – and that’s vital in exceptional weather like this.”
Highways England’s Head of Road Safety, Richard Leonard, said: “Gritters are out treating our routes around the clock but it is still important to drive to the conditions when snow is forecast.
“If you need to travel in the morning, make sure you keep your distance and reduce your speed because, even in conditions that seem normal and when the snow is not settling, it can be slippery if ice patches have formed, or where fresh salt has not been worked into the carriageway.
“Drivers should plan their journeys, monitor weather reports and pack a snow kit of blankets, food, water and a shovel if they really need to travel.”