Transisition Periods

This pattern is most likely to bring a widespread significant snowfall to the Whistler area. At the surface there is an intense arctic anticyclone in place over the interior of British Columbia providing a source of cold, dry air. Outflow winds help form a coastal atmospheric trough along the British Columbia and Washington coasts. The development of approaching Pacific cyclones will be enhanced by the coastal trough. Significant snowfall may accompany the overrunning of entrenched arctic air at and near the surface by the moist southwesterly flow in advance of the approaching Pacific cyclone. Normally, lowland snow will transition to rain as the cyclone approaches or passes to the north of the area but a cyclone passage to the immediate south of the region may result in an allsnow event. This pattern can bring widespread heavy show to the region. . Trapped cold air in the Whistler valley may briefly permit the occurrence of freezing rain.