Mountain Weather Forecast

Weather Synopsis for Sunday & Saturday

A trough lingers over the western US. A general break between active weather patterns has allowed for some weak instability to build in the afternoon with scattered clouds and isolated snow or graupel showers, particularly along the Cascade West slopes. Some high clouds are increasing over the Olympics ahead of the first in a series of poorly-defined, but moisture-laden systems which should approach the region on a NW flow, riding over a large ridge covering much of the eastern Pacific Ocean. The systems will bring lots of precipitation to the mountains, moderate to strong generally westerly flow, and rising snow levels. Significant amounts of snow will fall at many low to mid-elevation sites before many of these areas eventually see a changeover to rain up to approximately 4,000 ft in the Cascades. The systems have very little upper-level signature and generally weak surface fronts. 

On Sunday night, a warm front arrives, bringing increasing wind speeds, a slight wind shift from W-SW to W, a warming trend, and increasing light snow.

Monday should see light to moderate rain and snow as snow levels gradually approach Snoqualmie Pass level by the end of the day and moderate to occasionally strong crest-level W-SW winds. 

Monday night, a second system arrives on a NW flow as snow levels continue to rise. Snow will eventually change to rain at Snoqualmie Pass and may change to rain or mix with rain at Stevens Pass as well, but not before significant accumulations of snow. Rain and snow will become moderate to occasionally heavy, with much more precipitation in the Washington Cascades than near Mt. Hood.

The warming Monday and Monday night is in part a response to an eastward shift of the broad Pacific Ridge, forcing the storm track farther north and moving our forecast region into the warm sector of the active weather pattern.