Avalanche Forecast

The next front will begin to move over the Northwest Thursday afternoon and night. This should mainly bring increasing moderate to heavy snow to the Northwest Cascades Thursday afternoon with less snow through the daylight hours along the rest of the Cascade west slopes. Increasing SW-W alpine winds should generally be seen in all areas on Thursday.

Existing wind slab should linger and possibly further build on NW-SE aspects along the Cascade west slopes on Thursday.  New wind slab is likely to build in the Northwest Cascades on NW-SE aspects Thursday afternoon due to the incoming front and a greater wind slab danger will be indicated for that area. Remember to watch for wind transported snow on other aspects as well in all areas.

Existing storm slab may also linger along the Cascade west slopes on Thursday.  New storm slab is likely to build in the Northwest Cascades Thursday afternoon due to the incoming front and a greater storm slab danger will be indicated for that area. Storm slab is generally found on more sheltered slopes that experience rapid snow accumulations for several or more hours.

Remember to change your plans if the weather deteriorates sooner than expected in any area.

The cornice accident at Washington Pass on Tuesday is a reminder to avoid ridges or mountain tops where there may be a cornice and avoid slopes below cornices.

Loose wet avalanches also won't be listed as an avalanche problem but it is March so watch for roller balls and loose wet snow deeper than a few inches in you are on solar slopes in sun breaks.

Further increasing alpine winds and snow with a further increasing avalanche danger should be seen in all areas Thursday night and Friday.

Weather and Snowpack

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

A series of disturbances in cool, NW flow aloft from Saturday through Tuesday caused periods of moderate to strong SW-W alpine winds and have deposited significant snow.  Very strong W winds decreased on Wednesday following the last front. The 4 day storm snow amounts range from 18-40 inches along the Cascade west slopes.

See the information near the top of the Avalanche Forecast tab regarding the cornice accident at Washington Pass on Tuesday.

Recent Observations

North

NWAC observers Lee Lazarra and Simon Trautman along with a couple NWAC forecasters toured the Mt. Baker backcountry Tuesday 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.

The Mt Baker patrol on Wednesday mainly reported areas of 6-8" storm slab triggered by explosives and skis.

Central

NWAC observer Ian Nicholson was at Stevens Pass 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. 

In contrast NWAC observer Jeremy Allyn was in the Crystal backcountry Monday and did not find a loose-dry problem in that area. However, locally increased winds early Monday afternoon were transporting snow and building shallow, but touchy wind slabs on some cross loaded features, even in the below treeline band.

Heavy snowfall intensities Monday afternoon and evening in convergence at Snoqualmie Pass caused an extensive natural cycle of 10-12 inch deep storm slab avalanches.

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.

A couple reports from the Stevens Pass area via the NWAC Observations page for Tuesday indicate minor wind slab development near ridge tops and small ski triggered wind slab, storm slab and loose dry avalanches. The Valentine's Day crust was seen down 60 cm. Likely loose wet debris was noted on the south side of Mt Lichtenberg.

The Alpental patrol on Wednesday morning reported some 8-10" storm slab by ski tests. By afternoon wind affected snow on the upper mountain and sun affected snow on the lower mountain were giving bad ski conditions.

A report via Turns All Year for Wednesday for the Alpental Valley also indicated winds and warming were beginning to give beginning to cause snowpack cracking and was beginning to create new wind slab.

South

NPS rangers at Mt. Rainier National Park on Saturday 2/25 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 2/26 reported small and predictable, but fast moving loose dry avalanches on steep N-NE slopes near treeline. 

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