By Harry Stedman & Louise Sassoon A 24-hour yellow snow warning has been issued for the northern half of England and much of Wales on Thursday and Friday. The Met Office said a whole day of potentially heavy snow could lead to some disruption, with power cuts and travel delays possible. Up to 20cm could fall over high ground, according to current forecasts, while 1-2cm is widely possible at low levels. The warning runs from 3am on Thursday to 3am on Friday and stretches from Cumbria and the Scottish border down to Cambridgeshire and the Midlands in England. All of northern and central Wales, i…