Arctic air will sweep across western Canada and parts of the US early this week, leading to a cold snap that will probably last through the rest of this week and possibly beyond. By Wednesday, temperatures in western Canada could be as much as 10-15C below the seasonal average. Minimum temperatures in Calgary and Edmonton could plummet as low as -30C by Friday, with some rural areas experiencing even lower temperatures. In contrast, temperatures on the east coast will be significantly above average, with Ottawa reaching highs of about 5C, almost 10C above the seasonal average. The cold spell will spread into northern and western parts of the US by Friday, with temperatures widely reaching 5-15C below average. Three storm systems have hit the US in the past few days and continuing into this week. The first affected the north-east, with about 40 million people in parts of the New England and northern mid-Atlantic regions placed under winter storm alerts between Saturday afternoon and Sunday. According to the National Weather Service, parts of the north-east and central Appalachians expected to receive 4-8ins (10-20cm) of snow on Sunday. Between 6-12ins of snow had also been reported across parts of the upper Hudson River valley by Sunday. The second storm system affected the Rockies late this weekend, and will bring further heavy snow and strong winds over the plains and the midwest through the early part of this week. The highest accumulations are expected to be across parts of the midwest, where locally up to 12ins is likely, although at least 6ins is expected between northern New Mexico and the Upper Peninsula of Michigan. Heavy snowfall, alongside gusty winds in excess of 50mph, will cause extremely dangerous travel conditions and near-zero visibility at times. The third storm system arrived into the Pacific north-west late on Sunday, bringing heavy coastal rain, mountain snow and strong winds until the middle part of this week. This winter storm will probably bring several feet of snow across the Washington and Oregon Cascades, peaking on Tuesday and Wednesday.