‘Dangerous’ -40C gales threaten to scour the US through the rest of the month as the nation braces for one of the most savage mega-freezes ever recorded. A 1,600-mile cascade of ‘brutally’ cold air pouring in from the Arctic is likely to topple January temperature records. The big freeze follows an assault from a trio of storms – Ember, Finn and Gerri – which lashed the States with torrential rain, snow and furious winds. Now, cold winds passing over the Great Lakes will offload torrents of snow sparking warnings for severe disruption. The National Weather Service (NOAA) has in force advisor…