By Liam Doyle Weather maps show a 685-mile snow bomb is making its way to the UK with forecasters predicting the month will end with a wintry whiteout and plummeting temperatures. The mercury has climbed into the mid-teens in parts of the country this week, with London reporting 16C highs on Wednesday, which is expected to hold over the weekend and into next week. Beyond then, the picture becomes less clear, as maps show a cold snap descending on the country just days before it officially becomes spring. Temperatures appear set to become unseasonably chilly, even dropping below zero for the fi…