Tomorrow is forecast to be even more severe with hail, sleet, snow and thunder all on the cards.
Earlier today the area affected was the extreme west of West Sussex but this has recently been extended to cover all of the South.of England.
The Met Office is forecasting "persistent and heavy snow" in the regions between 9pm and 5am, with likely delays on the roads and "a risk that some vehicles and passengers could become stranded". "In addition some roads and pavements will turn icy, increasing the chances of accidents or injuries".
"The location of the most damaging winds is now uncertain, although parts of northern and eastern England along with southern Scotland now look more at risk".
All schools in the Scottish Borders and more than 120 in Northern Ireland have been shut today in the wake of heavy snow, leaving thousands of children stuck at home.
The warning comes as an Atlantic depression is set to bring scattered snow showers to northern parts of the country.
But other parts of Scotland have been blanketed in snow as forecasters warn of plunging temperatures and possible disruption.
The largest accumulations of snow will be over high ground, with more than 10cm building up above 200 metres.
"There could well be some hail and lightning around as well, particularly over western Scotland". The wintry showers are expected to last until 3am on Wednesday.
Thus, yellow warnings are in place for both Thursday and Friday in most areas of Northern England and Ireland.
'It is also going to be accompanied by some cold winds as well, gale-force winds at time across the south, mainly coastal sites and exposed hills.
Very strong winds will affect parts of the United Kingdom during Wednesday (January 17) night and into Thursday.
Along with the strong winds, a spell of heavy rain can also be expected, turning to snow for a time with the potential to add another 2-8 cm to snow depths in some places.
Storm Fionn will bring 80mph gusts, as well as eight inches of snow throughout the North West and North East of England, as well as Scotland, where an amber weather warning is in place.