Avalanche Forecast

On Thursday, alpine winds will by light and freezing levels should remain around 10000 feet. Very warm temperatures and the strong late March sun will maintain wet snow concerns as the main avalanche hazard Thursday. High freezing levels, light winds and sunny skies over the next several days will increase the hazard, causing natural loose wet avalanches on solar aspects and increasing the odds for low likelihood/high consequence problems such as cornice failures.  

Melt-freeze crusts can quickly break down with intense spring sunshine. In areas that have received more recent snowfall, small loose wet avalanches have the potential to entrain deeper layers. Be aware of terrain traps where even a small loose wet avalanche could have unintended consequences. Plan to avoid steep solar slopes by late morning/mid-day to minimize the problem.    

The likelihood of triggering older wind slabs continues to diminish, however, in isolated areas above treeline, a mix of older wind slab on lee easterly aspects and newer wind slab on the south through westerly aspects will maintain wind slab potential on a variety of aspects. Watch for cracking and firmer or chalky wind transported snow. 

Many areas have massive cornices along ridge-lines, watch for those overhead hazards. Unlike the loose wet problem, you may not have much notice that a cornice is about to fail. Cornices can break much further back on ridges than expected and releases can be unpredictable during the spring.

Weather and Snowpack

Snow accumulations Wednesday 3/23 to Friday 3/25 varied based on proximity to the Cascade crest and higher terrain with about 12 inches at the NRCS Lyman Lake Snotel, 6 inches at Harts Pass and next to nothing at Blewett, Mission Ridge and Berne weather stations. 

A strong front crossed the Northwest Sunday morning followed by a large upper trough and a cool unstable air mass Sunday afternoon and evening. Snowfall accumulations were light along the east slopes of the Cascades with only a few inches of new snow seen at the higher elevation stations near the crest. The highest totals were likely downwind of a Puget Sound convergence zone east of Snoqualmie Pass Sunday evening. 

Sunny skies on Tuesday were accompanied by a slow warming trend and moderate NE crest level winds along the east slopes. While valley locations like Lake Wentachee and Mazama hit 60 F Tuesday, Mission Ridge summit temperatures stayed near freezing with wind speeds averaging in the 30s and gusts 55-70 mph out of the NE Monday night through Tuesday afternoon. 

Frequent March storms have built large cornices along ridges in many areas.

A spotty layer of surface hoar was buried on about 3/12 mainly in the northeast Cascades with the terrain most suspect being N through E facing slopes. The last known human triggered avalanche on this layer was in the Washington Pass area on 3/19 and the persistent slab problem has been removed from the east slopes forecast moving forward. 

No avalanches have been noted for quite some time on a persistent surface hoar layer buried February 27th in the Washington Pass area and to a lesser extent the central-east zone. Avalanches releasing on or down to this layer are unlikely.   

Recent Observations

Mission Ridge pro-patrol reported strong west winds Thursday morning 3/24 but little in the way of avalanche concerns in area due to the lack of new snow. On Saturday they reported minor small point release loose wet avalanches and minor rollerballs.

Tom Curtis was out in the Table Mountain area of Blewett Pass on Monday and found about 6 cm of new snow in wind sheltered areas with up to 20 cm on lee north through east aspects near treeline. No recent avalanche activity was noted in the Blewett Pass area.