Avalanche Forecast

An approaching disturbance should bring renewed light to moderate snow at low snow levels with strong ridgetop winds overnight Tuesday and early Wednesday.

This should build new unstable wind slabs in exposed terrain, near and above treeline and some isolated features below treeline. Wind slabs should build on primarily on NW-NE-SE facing slopes, but may build on a variety of terrain features.

Unstable storm slabs should develop by Wednesday in all terrain, especially following rapid loading in areas receiving the greatest new snow amounts.

Expect dangerous avalanche conditions Wednesday. Evaluate the snow and terrain carefully and change your mindset accordingly to more conservative choices. 

Weather and Snowpack

The most recent warm and wet SW storm arrived on Valentines Day 2/14 and formed the uppermost, very strong rain crust in our snowpack. 

A series of disturbances in cool, NW flow aloft from Saturday night through Tuesday have deposited significant amounts of very low density snow. The three day storm snow amounts are variable throughout the west slope regions, ranging from 10-20 in the Mt Baker and Stevens Pass areas, and 20-40 inches at Snoqualmie Pass and the Mt Rainer areas.

Heavy snowfall intensities Monday afternoon and evening in convergence at Snoqualmie Pass caused a natural avalanche cycle.

Winds are increasing Tuesday evening as the next storm approaches the area. This is beginning to build new wind slabs and stiffen surface snow forming the beginnings of a new storm slab problem.

Recent Observations

North

NWAC observers Lee Lazarra and Simon Trautman along with a couple NWAC forecasters toured the Mt. Baker backcountry Tuesday, 2/28 ahead of the incoming storm. Timing can be everything, as surface snow conditions remained excellent with no real avalanche problems encountered. Low cohesion snow was well bonded to the Valentine's crust and continued to provide excellent tour conditions.   

Central

NWAC observer Ian Nicholson was in the Stevens Pass area on Saturday and found sun crusts affecting the snow surface on an increasing range of solar aspects with shallow amounts of new snow below treeline above the stout 2/14 crust. The weak surface snow near treeline was beginning to be transported by westerly winds beginning around mid-day. Ian was in the Yodelin area Sunday and found 6 inches of low density snow had refreshed the snow surface. Small loose dry avalanches were easily ski triggered on steep test slopes. Shallow new wind slabs were found on lee aspects near ridgetop. Ian was on Skyline Ridge Monday and reported fast moving loose-dry avalanches involving the most recent storm snow easily triggered in steep terrain above about 35 degrees. 

On Sunday, Alpental pro-patrol reported widespread and easily ski triggered, loose-dry avalanches running fast and entraining the surface snow on steep slopes. 

Contrastingly, NWAC observer, Jeremy Allyn was in the Crystal backcountry Monday and noted the loose-dry problem was non-existent in that area. However, locally increased winds early Monday afternoon quickly transported surface snow and building shallow, but touchy wind slabs on some cross loaded features, even within the below treeline band.

Dallas Glass toured on Mt Snoqualmie Tuesday and noted the remnants of the storm slabs that formed late Monday during heavy snowfall. These storm slabs were easily triggered with skis and released within the most recent storm snow. However, a weak layer was found at a thin melt-freeze crust about 8 inches above the rain crust and in deep tests showed propagation was likely. A key takeaway for the Snoqualmie area is just how deep the storm snow above the Valentine's crust is, ranging from 3-4 feet! Avalanches stepping to a deeper weak layer would be very large and dangerous.

South

NPS rangers at Mt. Rainier National Park on Saturday initially relayed a report that five people were hit by a large loose dry avalanche that naturally released in the Fly Couloir on Lane Peak in the Tatoosh Range. Two or three individuals were partially buried, able to self-excavate but suffered some minor injuries. 

Backcountry observations from the Crystal area on Sunday reported small and predictable, but fast moving loose dry avalanches on steep N-NE slopes near treeline. 

An NPS ranger at Mt Rainier reported increasing winds Tuesday evening, 2/28. Surface snow was becoming wind stiffened and beginning to fail as slabs, even on shallow angled terrain.