"This will result in a significant impact to the evening commute with snow covered roads and poor [visibility] in moderate/heavy snow".
The winter storm will bring blizzard-like whiteouts.
The agency has issued a special weather statement as a result of a possible winter storm arriving Tuesday.
Let's now explain what's happening. Hundreds of flights were canceled in Seattle and Portland, and heavy snow drifts closed major highways in eastern Washington. Cars are pictured driving on snow and ice on Interstate 405 approaching Kirkland, Washington, on Saturday.
In the thicker part of the wedge, the snowflakes melt into drops, which survive the trip all the way to the surface...which is below freezing since that warm air is still aloft.
About 50,000 residents are said to have lost power across the state, U.S. media report.
Snowfall amounts may be higher should the switch over to freezing rain not occur.
Total snowfall amounts of 20 to 30 cm are expected before the snow tapers off Wednesday afternoon. In Seattle, snowfall from February 3 and 4 lingered into the week as below-freezing temperatures gripped the area.
There could be some lake enhancement overnight into Tuesday morning with a strong east to northeast wind.
Light snow started to make its way into the interior lowlands in the late afternoon, the weather service said. The winds are really expected to be strong tonight between 15 and 25 miles per hour.
Later in the evening, the back side of the storm will transition the precipitation back to snow. We get another system Thursday into Friday. Today, we'll have a lull during the day and evening with highs in the upper-20s with breezy conditions.