West Slopes North - Canadian Border to Skagit River
The Bottom Line: Significant new snow and moderate to strong winds well above treeline have created winter-like conditions above 7000 ft. Don’t let your guard down if you head to higher elevations.
Weekend Snow and Avalanche Discussion
Over the last week, we transitioned back to cooler temperatures after a prolonged warm and dry spell from May 4th - May 13th. Since May 14th, most NWAC stations have remained above freezing, with some solid refreezes at our highest elevation sites.
A moisture-laden frontal band brought significant precipitation and some convergence activity to the region later Thursday through Friday morning. The west slopes of the Cascades received 1.00-2.50” of water equivalent, while the east slopes of the Cascades and Mt. Hood received less than an inch.
Above 6000-7000 ft, some of this precipitation has fallen in the form of snow, creating a return to winter-like conditions at higher elevations above 7000 ft. These higher elevation areas are where the avalanche danger will be most elevated this weekend.
Graph: Weather stations showing a return to cooler, more seasonal conditions after a prolonged heat wave in early May.
Expect a mix of clouds and sun on Saturday with freezing levels rising to 7000-8000 ft and light to occasionally moderate East winds developing at all elevations. Late Saturday, a band of rain should begin lifting northward across the Oregon Cascades and into the Washington Cascades overnight and lingering over the region through Sunday. Snow levels are expected to be in the 6000-7000 ft range. The North Cascades should remain warmer and drier than other areas.
Recent Avalanche Activity
Some unusual avalanche activity continued to be reported through the early May heat wave. During that time frame, reports on the NWAC observations page documented a climax avalanche near Washington Pass, a very large avalanche that may have been partially geothermally triggered on Sherman Peak (Mt. Baker), along with evidence of wet slab and loose wet activity.
Since the unsettled weather began, reports have been very limited. A large loose wet avalanche observed on the south side of Mt. Rainier at very high elevation reminds us that the fresh snow has created new avalanche danger.
New Snow Avalanche Concerns at Elevations above 7000’
Wind Slabs - Fresh snow has drifted to around ~2 ft (50-70 cm) deep in some areas on Mt. Rainier. Watch for wind slabs on lee slopes or under cornices. Look for evidence of wind transported snow and consistently probe the snow above a firm or refreezing snow surface to check for a punchy snow character. Avoid wind-loaded slopes and convexities over 35 degrees.
Loose Wet Avalanches - Loose wet avalanches will start as soon as this fresh snow receives direct sunshine and these avalanches are expected to entrain enough snow to become large and powerful. Get off steep slopes if the surface snow becomes wet and deeper than your ankle. Plan your travel to avoid exposure to higher elevation slopes capable of producing large wet snow avalanches as the sun comes out and temperatures rise.
Other terrain-related hazards
Cornices are likely to be weak and are more likely to break if they are overhung and receiving direct sunshine or rainfall. Limit your exposure to large cornices as you travel.
Creeks are full and moving rapidly. They can present a serious impediment to travel at this time of year.
Below-normal snow coverage exists at all elevations. Lower elevations have melted out, mid-elevations have melted back rapidly, and rocky terrain at higher elevations is increasingly exposed. Don’t assume that areas you traveled in at this time last year will look the same.