The snow began over Whidbey Island late in the afternoon, and then was driven south by strong, cold winds from out of Canada. That cold, dry north wind met with warmer, moist area that had settled in over south Snohomish, King and Pierce counties, resulting in heavy snowfall and quickly dropping temperatures. On our Stormtracker 7 Pinpoint Doppler radar, the snowline was easily seen marching down I-5 from south of Everett and right through Seattle just as the Monday evening rush hour was building. What's more, with Seahawks traffic and roads turning to ice, many commuters were caught far from home on a night when even driving a few miles could take hours. In the middle of it all, we even saw a little "thundersnow", with lightning strikes on jets near SeaTac.

The bitterly cold air that triggered the snowfall is now here to stay, with sub-zero wind chills for a windy Whatcom County today, and temperatures elsewhere that will likely be below freezing all day. This may set us up for more snow late Wednesday night, before we warm up and see some rain by midday Thursday.