Avalanche Forecast

The pattern is a tricky forecast timing-wise for the daylight hours on Sunday. The timing and track of the incoming low pressure system remains pretty consistent among the numerical weather models.

The deep low pressure system should move across the northwest tip of the Olympic Peninsula and across south Vancouver Island Sunday afternoon and evening. This should bring stormy weather and moderate to heavy snow to east slopes Sunday late afternoon or evening. A vigorous, strong front should rapidly cross the area and cause rapidly shifting winds Sunday evening.

The main avalanche problems on Sunday through most of the daylight hours should be winds transporting and redistributing new or recent snow onto lee slopes. This is likely to be northwest to southeast slopes at higher elevations. New or recent shallow storm slab should also be possible where there has been rapidly accumulating new or recent snowfall.

Rapidly changing weather and snow conditions are expected east of the crest Sunday afternoon or evening. Be ready to change your plans if the storm arrives and conditions deteriorate sooner than expected.

The persistent slab avalanche problem will only be listed in the northeast zone and is most likely to be found on non-solar aspects in the above and near treeline band and stretching into the upper portion of the below treeline band.  This interface is likely getting harder for a human to trigger but if triggered is capable of producing large avalanches. Be aware that at depths approaching the 1 m mark the extended column test becomes a less reliable indicator of propagation across a column. Deeper tests like the propagation saw test or deep tap test may help but layer identification and terrain selection are your best friends for managing a persistent slab danger.

Weather and Snowpack

During a period of fair weather in late February, widespread surface hoar formed in the northeast zone mainly surviving outside of steeper solar aspects and wind affected terrain. A weak front buried the surface hoar layer in the Washington Pass area about 2/27 and to a lesser extent the central-east zone.  

The nonstop active weather pattern continues to push a storm system through the PNW almost every day or two with fluctuating but generally moderate snow levels.

The last storm impacted the area Wednesday through Thursday with a warming trend that peaked Wednesday night and very strong winds seen throughout the Cascade range. Generally 1 to 1.5 inches of water accumulated along the east slopes in the 24 hours ending 4 am Thursday. Snow levels rose above 5000 feet in the Mission Ridge area Wednesday night but stayed lower closer to the Cascade crest and in the northeast Cascades. About 6-16 inches of snow accumulated through Thursday morning with the higher tallies of over a 1 foot seen at Holden, the NWAC station at Washington Pass and the NRCS sitess at Lyman Lake and Hart's Pass.

A front on Saturday is causing west-southwest winds and there should be a couple inches of new snow at most sites by Sunday morning.  

We are no longer tracking any layers of concern formed earlier this winter in the mid or lower snowpack due to lack of recent activity at these interfaces and confirming field observations. 

Recent Observations

Strong winds on March 3rd caused widespread natural wind slab avalanches in the NE zone. While many were contained to the recent storm snow, one larger slide on a N-NE aspect at Windy Pass likely released down to the 2/27 PWL. The last known human triggered avalanche on this layer was also in the Washington Pass area on March 2nd. 

Mission Ridge pro-patrol reported a very active day of control on Thursday, March 10th with 1-4 foot slides produced during control work on lee slopes below ridges. Wind slabs were sensitive and ran far.  Widespread cornice growth was also noted along ridge lines.

The North Cascade Guides report for the Washington Pass area on Friday indicates 20-50 cm of HST on lee slopes. Several pits had a mix of homogeneous snow or crust in the top meter of snow. Tests gave no results or RP results including on the 2/27 interface. Crowns or debris with sizes to 2.5 was noted from an avalanche cycle on Wednesday to Thursday.