Mountain Weather

We'll be in active pattern through much of the work week but there's still a lot of uncertainity regarding the mid/late week weather systems. Starting this afternoon, we are in post-frontal flow with a slow cooling trend underway and leftover showers over the area. Showers will be most intense over the Mt Hood area this evening. A trailing upper level trough will pass through and shift the shower focus to the central Cascades with a Puget Sound Convergence Zone later tonight through Monday morning. By Monday morning, snow levels will have fallen into 2000-2500' range and most areas should find a few inches of fresh snow along the west slopes of the Cascades, Passes and Mt Hood.

The trough's passage overnight will also create some strong west winds overnight, and they will slowly taper down on Monday. A weak secondary weather feature will move into the Cascades later Monday afternoon, producing some light, but rather humdrum snow showers.

Scattered showers will quickly wind down Monday evening with a brief period of drier weather on tap Monday night through Tuesday morning. Then, warm frontal moisture will begin to move into the southern half of the forecast area in the afternoon. Areas north of I-90 are likely to see light snow or dry conditions for much of Tuesday, while the south Washington Cascades in particular should see snow begin to pick up during the afternoon hours.

It's a warm, wet, and windy day across much of the forecast region. A frontal system will continue to bring rain and high elevation snow to the Pacific Northwest this afternoon and evening. You may encounter periods of heavy precipitation and gusty winds. The storm peaks in the evening, before quickly exiting to the south and east. By Sunday morning, all the lingering showers should be wrapped up, except for areas along the Columbia River like Mt Hood and Mt Saint Helens. 

While it seems fairly certain that most locations in Washington start Sunday dry, after that, all bets are off. A short wave feature tries to lift precipitation northward out of Oregon, but weather models don't agree on how far into the Cascades it reaches or how much moisture it brings. Some show isolated showers all the way to the Canadian border, while others keep nearly the whole state dry. Not surprisingly, there's low confidence in exactly how this will play out. Even still, a few trends emerge. The best chance for precipitation will be from about I-90 southward. The further south, the more likely you'll see rain and snow. Precipitation should be about equal on both sides of the Cascade crest. Locations further north and west could see significant sun breaks. And the winds should generally be light. This pattern (and problem) continues Sunday night. 

A low pressure system passing to our north spins a wave of moisture into the Pacific Northwest on Monday. Even though it doesn't appear like a lot of moisture is associated with this feature, colder air should allow for snow to accumulate near and below pass elevations. Moderate westerly winds help showers continue to wring out a few more inches of snow, mainly near and west of the Cascade Crest, through the day.