Mountain Weather

Light snow showers along the west slopes of the Cascades will taper off overnight. On Tuesday, the main weather event will begin as warm frontal moisture arrives along the coast in the morning, and quickly slides into the central Cascades to Mt Hood by late morning/mid-day. Snow levels will initially stay below Pass and most trailheads during the day on Tuesday, and snowfall rates will become moderate to heavy by sunset, most likely from the Snoqualmie Pass corridor to the far south WA Cascades in the afternoon and early evening. Even this close to the onset of the storm, there's a fair amount of uncertainity regarding the northern/southern impact of the storm. There's higher confidence that southerly winds will ramp up in the afternoon as storm conditions intensify.

Moderate to locally heavy precipitation will continue through the first half of Tuesday night, but snow levels will rise more agressively, with a change to rain at mid-elevations for the Mt Hood area and the south WA Cascades first. As the warm frontal precipitation begins to taper off Wednesday morning and milder air continues to punch inland with westerly flow aloft, we may see mixed precipitation including freezing rain/drizzle in Snoqualmie Pass, with a chance along the east slopes of the Cascades near and south of I-90.

We should see a short break in the action on Wednesday as another warm front approaches the area. Milder air will have moved into the region at this point, and snow levels will be between 4000-6000' for northern/central Cascades and 6000-8000' for the S. Cascades and Mt. Hood area.

Buckle up! We're in for a very wild and extremely wet few days! A pair of atmospheric rivers will take aim at the Pacific Northwest, bringing eye-popping amounts of precipitation, generally warm temperatures, and very strong and gusty winds. We'll be measuring the water in multiple inches range. Yikes!

The first tidal wave of moisture is arriving as I type (6am). Look for very heavy rain and high elevation snow to develop in the mountains by mid-morning. Once it starts, it won't let up for about 18 hours. Areas near and west of the Cascade Crest could see numerous hours of 1/4 to 1/3 inch of water per hour. Warm air will cause snow levels to climb during the day, peaking in the late afternoon/evening around 6500-7500 feet. Very strong winds should help precipitation pour across the crest throughout much of the storm. So, while east-side zones won't see quite as much rain and snow as their western neighbors, this will still be a major event.

The atmospheric river shifts south into Oregon in the wee hours of Tuesday morning. This keeps the firehose going for Mt Saint Helens, Mt Adams, and Mt Hood. Right now, it's hard to say if places like Mt Rainier, Crystal, and White Pass stay in the bullseye or see a break from the storm. Further north, a cold front will drift down from Canada, helping temperatures to cool. Sadly, as snow levels drop, the moisture tap turns off. As a result, places near I-90 and north should see a break in the storm on Tuesday with just a few light showers and maybe even a few moments of sunshine.

The rollercoaster ride isn't over, though. The second onslaught of precipitation arrives Tuesday evening, bringing another round of very heavy rain/snow, rising snow levels, and very strong and gusty winds.