Avalanche Forecast

High clouds in advance of a weak weather disturbance should make for a mostly cloudy day over the north Cascades while more sunshine is seen further south. Temperatures will remain cold but winds will be much lighter on Thursday.

Moderate to locally strong E-NE winds Tuesday night and Wednesday have loaded unusual aspects and built wind slab in all elevation bands. Allow fresh wind slabs time to stabilize and avoid terrain where even a small slab avalanche could have unintended consequences. Remember to watch for firmer wind transported snow on all slope aspects or cross loaded slopes especially in areas with varied terrain and modified wind directions. 

Along all of the east slopes the 12/17 PWL persistent slab problem is gaining strength, becoming more deeply buried and less sensitive in snowpack tests. However, continue to avoid large open terrain in areas where an overall shallow snowpack exists like the Mission Ridge/Blewett Pass area or where you find this layer in snow pits, especially if you experience direct observations such as whumpfing or shooting cracks.

Weather and Snowpack

A low pressure system moved south over western Washington on Saturday night followed by cold Arctic air. NWAC stations along the east slopes had West winds Saturday and up to about 4 inches of snowfall by Sunday morning.

An unusual moist reverse orographic east flow caused snow especially along the east slopes of the central to south Cascades Sunday afternoon and night. NWAC stations along the east slopes had a shift to NE winds and another 0-34 inches of snow on Monday morning with the most snow in the central to south part such as at Mission Ridge.

Fair cold weather with east winds were seen on Monday and Tuesday. Fair and cold weather continued Wednesday with easterlies moderate at Pass level and strong NE winds near ridgetops and above treeline seen at the Washington Pass and Mission Ridge stations. 

Recent Observations

Tom Curtis was out at Mt. Lillian Friday 12/30 and found reactive wind slabs along ridges with shooting cracks and whumpfing on north aspects near 5900 feet. The wind slab was likely collapsing down to the 12/17 PWL about 25-35 cm down. Wind slabs were found on NW-E-SE aspects with some wind loading apparent well below treeline.

Ski tourers in the Washington Pass area Saturday 12/31 reported no results from hand shears in the near and below treeline bands and no avalanches while avoiding possible wind loaded terrain above treeline. Nice, low cohesion surface snow conditions were reported below treeline. 

On Sunday 1/1 reports from multiple snow pits by Mission Ridge patrol testing the basal facet layer, now indicate a much stronger more settled snowpack from a week ago. The basal facets remain intact, but show signs of rounding and overall consolidation and bonding.

The NCMG at the hairpin at Washington Pass on Sunday 1/1 found that new snow was causing loose dry avalanches on steep terrain. North winds were seen to be quickly forming touchy new wind and storm slab.

The Mission Ridge ski patrol had their hands full with about 34 inches of new snow and strong northeast winds on Monday morning. It was not possible for them to visit lee S-W slopes were likely new, deep wind slab was expected.

The NCMG was out again at the hairpin at Washington Pass on Monday and found 20-25 cm of storm snow and no significant signs of instability.