Avalanche Forecast

Wet avalanche conditions will quickly develop Sunday as warm air temperatures and sunny skies affect the snowpack. When you see new rollerballs, observe fresh fan-shaped debris, or experience wet surface snow deeper than your ankle, you may be able to trigger loose wet avalanches on similar slopes. Do not underestimate these loose wet avalanches. Observations from this week have shown that many small slides have gouged into older snow layers, grown large, and traveled farther down slope than normal.

Many cornices have grown large over the winter. This time of year, warm sunny weather causes them to droop and eventually fail. This warm-up may be significant enough to cause this to occur. Do not linger in areas where cornices are above you. Choose travel routes and techniques that limit your exposure to these potential ticking time bombs.

We have received reports of isolated very large wet slab and glide avalanches from most areas over the past week. Many of these avalanches appear to have been triggered by cornice falls or loose wet avalanches. During significant warm-ups such as this, minimize your time in very large avalanche paths by choosing routes and techniques that reduce your exposure to this low-likelihood but high-consequence scenario.

Small lingering wind slabs from Saturday may still be found at higher elevations. You are most likely to trigger a wind slab below cornices, near convex rollovers, or on unsupported slopes. Use visual clues such as cold dry surface snow, fresh cornices, and snow drifts to identify and avoid these wind loaded features

Other springtime hazards exist in the mountains. Creeks have begun to open, running high and fast with snowmelt. Use caution and choose your creek crossings carefully if you are traveling near or over large creeks.

In general 1-3 inches (3-8cm) of new snow fell in most locations Saturday. Winds during the storm drifted snow at higher elevations. Near and below treeline, this new snow fell on a melt-freeze crust. The thickness and strength of the curst depends on aspect and elevation. On shaded slopes above treeline, this new snow fell on strong settled snow.

The upper and mid snowpack is quite variable depending on aspect and elevations. In general, the upper snowpack consists of frozen melt-freeze crusts, weak large wet grains, and strong rounded grains. The 4/1 melt-freeze crust which may be the culprit in some of these recent very large wet slab avalanches is generally found 4-6 feet (120-200cm) below the snow surface.

Very large slab and glide avalanches have been reported over the last several days. Mt Baker, Stevens Pass, Alpental Valley, Chinook Pass, and the Mt Rainier area have all reported very large deep avalanches. They are a reminder that very large triggers, such as cornice falls or other avalanches, may trigger older deep layers that have become wet with recent rain and warm temperatures.

Observations

Stevens Pass

NWAC avalanche forecaster Dallas Glass traveled in the Stevens backcountry Saturday. Dallas found 1-3" (3-8cm) of new snow. He was able to trigger loose wet avalanches on steep slopes greater than 35 degrees. In areas where the slopes were longer, these small avalanches entrained additional snow and ran further than he expected.

NWAC professional observer Matt Primomo traveled in the Stevens backcountry Friday. A layer of weak large grain wet snow was observed near treeline (5800’). This weak layer was 14-30” (35-75cm) below the snow surface. Numerous loose wet avalanches were observed in the area from the last several days.

Snoqualmie Pass

NWAC avalanche forecaster Dallas Glass traveled in the Alpental Valley Friday. He found weak large grains of wet snow in the upper 30” (75cm) of the snowpack. He was able to trigger loose wet avalanches on small test slopes near and below treeline. This corresponded with numerous recent natural loose wet avalanches on all aspects.

Tuesday and Wednesday Alpental ski patrol reported glide avalanches in the Alpental Valley that entrained significant snow and traveled farther than normal.

South

NWAC professional observer Lee Lazzara traveled near Paradise Saturday. Lee found small shallow isolated wind slabs near treeline. While they were generally too small to pose a risk, at higher elevations they may be larger and more widespread.

We received several reports of a very large avalanche in the Frying Pan Creek drainage near Mt Rainier Thursday. The avalanche appears to be on a NE aspect around 7500’.

NWAC staff visited the Crystal backcountry Wednesday and Thursday. They reported many large overhanging cornices. Wind slabs in this area had bonded and gained strength. Surface snow on nearly all slopes showed signs of warm air temperatures.