Avalanche Forecast

The relatively high snow levels will continue with rain forecast below 6000-7000 feet through Tuesday morning. We should see a relative break in the steady precipitation Tuesday afternoon before another wave of moisture returns Tuesday night. Periods of moderate W-SW winds above treeline will continue to transport new and recent snowfall only for the upper portion of the above treeline band Monday night through Tuesday. 

We have already experienced a region-wide avalanche cycle such that the overall likelihood of wet snow avalanches have diminished. However their destructive potential remains high. Realize that wet snow avalanches, specifically wet slab avalanches, are very hard to predict and demand an extra amount of caution when engaging with avalanche terrain.

Loose wet avalanches are likely on steeper slopes with the additional rainfall. While most loose wet avalanches will be shallow, a few may gouge down to deeper layers and become more powerful than you expect. 

Cornices will be weakened and prone to failure due to rain and mild temperatures. Very large cornices have been reported in many areas and have been involved in recent accidents and close calls. A cornice failure could trigger a large and destructive wet slab avalanche. 

Wet slab avalanches are highly unpredictable and not necessarily tied to peak warming or rainfall. Glide cracks can indicate areas where wet slab avalanches are more likely to occur. Besides their destructive potential, wet slab avalanches often surprise backcountry travelers when they run further than expected. 

If you manage to venture into the above treeline zone Tuesday, expect new or previous wind slab mainly on NW-SE aspects due to recent SW-W winds. Continue to watch for firmer wind transported snow on all aspects especially in areas of complex terrain.

Weather and Snowpack 

The first week or so of March was very cool and snowy. NWAC stations along the Cascade west slopes piled up about 3 to 8 ft of snow with the most at Mt Baker.

A strong frontal system brought increasing precipitation and winds along with a warming trend to the Cascades on Thursday. On Thursday night rain pushed up to about 5000 feet in the northwest Cascades and about 6500 feet in the southwest Cascades. By Friday morning NWAC stations along the Cascade west slopes had about 1-2 inches of WE (water equivalent) but only 0-7 inches of snow (most snow at Stevens and Mt Baker). This load gave the snowpack a huge test and caused an avalanche cycle along the Cascade west slopes.

Another front crossed the Cascades on Saturday causing SW-W winds, snow at higher elevations and rain at lower elevations. NWAC stations along the Cascade west slopes had about 1-7 inches of new snow on Sunday morning with the most at Mt Baker, the top of Alpental and at Paradise.

A mild frontal system slowly sagged south across the Cascades on Monday with moderate to locally heavy rainfall. Rainfall totals through 5 PM PST (or 6 PM PDT)

Recent Observations

North

The Mt Baker patrol reported natural avalanches on Thursday night. A very large avalanche released during avalanche control work on Shuksan Arm Friday producing a 8 ft x 75-100 yd crown.

Shuksan Arm avalanche crown from Friday 3/10. Photo Mt Baker Ski Area.

Shuksan Arm debris on Friday 3/10. Photo by Sam Llobet, Mt. Baker Ski Area.

NWAC observer Lee Lazzara was out near the Mt Baker ski area on Sunday and reported 20-25 cm of homogeneous moist snow well bonded to the 3/10 crust over deep dense snow. Cornices were huge with ski triggered loose wet avalanches possible.

Central

The Stevens Patrol and Stevens and Snoqualmie WSDOT crews reported many wet slab and loose wet avalanches from control work and natural cycles Wednesday to Friday. Several large slab avalanches ran on the south side of Granite Mountain near Snoqualmie during this period.

The Alpental patrol reported a widespread natural cycle occurred Thursday night.

NWAC observer Tom Curtis made a trip to Rainy Pass just east of Stevens Pass from the Lake Wenatchee side on Saturday. He noted wind effects on nearby ridges and 1-3 days worth of old loose wet and wet slab releases. The upper snowpack consisted of a surface crust over right side up snow and no alarming results in snowpack tests in the area he traveled.

NWAC observer Jeremy Allyn was in the Alpental Valley from 3000-4000 ft on Saturday and reported evidence of the avalanche cycle on Thursday and Friday. A 2 inch thick surface crust was stabilizing underlying moist snow. Travel conditions were extremely difficult. 

NWAC observer Dallas Glass was in the Alpental Valley on Sunday and Monday and reported tough travel conditions (boot sucking goo) along with some rollerballs on steeper slopes. 

South

Dallas was in the Crystal backcountry on Friday 3/10 and reported a wet slab cycle occurred there on Thursday night with several releases on the ridge running from 3 Way to Crown point on W-NW-N slopes in the 5800-6000 range. Natural loose wet avalanches also ran from steep and rocky terrain.

The Paradise NPS rangers reported a large natural wet slab or loose wet avalanche covered the road Friday morning just up the road from the Nisqually Bridge. This occurred on a NW aspect at about 4500 ft.

Just above the Nisqually Bridge to Paradise on Friday morning. Photo Doug Jones.