Weather Synopsis for Saturday night through Monday

It's a quiet afternoon across the forecast region, but that's about to change. The mountains will look very different by tomorrow morning. An atmospheric river takes aim at the Pacific Northwest overnight bringing locally heavy precipitation, rising snow levels, and very windy conditions for the next several days.

Clouds continue to increase this evening ahead of the storm, but most trailheads stay dry. Precipitation arrives first in the Olympics, before spreading to the Cascades around midnight, and finally to Mt Hood and the easter portions of the zone just before sunrise. Initially warming with this storm will be slow, allowing snow to accumulate even at lower elevations before it switches over to rain. Snoqualmie Pass will probably change in the wee hours of the morning, but Stevens and White Passes should remain snow overnight. As the precipitation starts, look for winds to increase and become noticeably gusty. 

By Sunday morning, the fire hose is aimed directly at the Central Washington Cascades. Expect stormy conditions with heavy precipitation in the western Olympics, and near and west of the Cascade Crest. Lighter steady precipitation with the occasionally heavier shower will easily make its way further east. Temperatures should quickly rise as the storm continues to intensify. For most zones, rain could reach well into the upper elevations by the afternoon. On top of the heavy precipitation, very strong and even extreme winds will rake the mountains. 

The main band of precipitation lifts slightly northward Sunday night maintaining a steady stream of rain and high elevation snow from near Mt Rainier and I-90 northward. For the most part, winds also remain very strong and gusty. Basically, the storm just doesn't seem to let up. A bit more uncertainty arises by Monday. Some weather models keep the moisture coming, while others indicate a bit of drying and more of a showery pattern. Either way, snow levels will already be near or above most of our forecast elevations, so any precipitation that falls will almost certainly be as rain.