Observation: NWAC Forecaster

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Weather Summary

Unique warm, upslope weather pattern. The day started warm, but cooled after 12p. S1 snow mainly before 12p w another short burst around 2p. Overcast clouds gradually started lifting around 12p, becoming broken in the afternoon w periods of thicker/lower clouds. Very calm wind. Air temps rose above freezing below treeline, but remained cold above treeline.

Avalanche Observations

#	Date	Location	Size	Type	Bed Sfc	Depth	Trigger	Photos	Details
1	Apr 21, 2022 ()	Silver Star creek NW 5600ft	D1	WL-Wet Loose	I-New/Old Interface		N-Natural		Report
5	Apr 21, 2022 11:30 am ()	Silver Star creek NW 6200ft	D1.5	WL-Wet Loose	I-New/Old Interface		N-Natural		Report

Avalanche activity (and hazard) seemed to be limited to very specific asp/elev and timing. We saw and heard about 5 avalanches run on very steep NW aspects near treeline with the peak of warming with snowfall. Most (and the biggest) of these were initiated from rock faces shedding snow, and could have gouged below the 4/20 interface. A few very small loose wet avalanches and rollerballs ran below treeline in the 6,000-5,400ft range, though there was minimal snow available to entrain.

Snowpack Observations

Significant variation by elevation and aspect. Southerly aspects are bare below 5,000ft. Northerly aspects near and above treeline and most slopes above ~7,000ft hold a winter-like snowpack with minimal to no transition to melt forms.

Below 5,000ft in flat terrain to steeper N-NW, the 4/20 interface was a semi-frozen crust. New snow was 5cm or less, which began to melt into the old crust by afternoon. Above 5,000ft on Nrly, the 4/20 interface quickly became a thin, 4F+ layer of rounds and melt forms with mostly dry snow above and below.

Above 6,500ft, the new snow was dry and rested on the 4/20 which seemed to have been stiffened by both wind and possibly subtle melting/rounding from mild temps. About 60cm of settled snow accumulated since 4/8. Above 7,000ft, N-NW, HS was consistently greater than 350cm. We encountered areas of slight wind stiffened and wind-drifted slabs from 4/18-19 at 8550ft, N, just below the ridgetop. Hand shears produced hard, non-planar results ↓35cm. These were also unreactive to skiing.

A quick profile, 6,800, WNW:
0-13cm new snow, F+ hardness, mostly dry, 4/20 @ 13cm
13-33cm 4/18 snow, 4F+ hardness, dry, @33cm- hard, non-planar hand shears
33-60cm snow since 4/8, 1F, dry
60cm P-k hard, crust/debris, likely 4/7-8 warm-up

Avalanche Problems

Problem	Location	Distribution	Sensitivity	Size	Comments
Wet Loose	N E S W	Isolated Specific Widespread	Unreactive Stubborn Reactive Touchy	D1 D1.5 D2 D2.5 D3 D3.5 D4 D4.5 D5	Layer Depth/Date: 10-20cm, mostly on 4/20 interface/crust. Some may have gouged a bit deeper into snow that fell 4/19 Comments: Hazard was very specific in distribution and timing tho significant enough to injure a person. Hazard was generally 5,500-7,000ft, most widespread/prolonged near treeline, but otherwise isolated and fleeting. Near treeline, naturals occurred during peak warming/snowfall 11:30-45a, and likely with some sun mid-afternoon.
Wind Slab	N E S W	Isolated Specific Widespread	Unreactive Stubborn Reactive Touchy	D1 D1.5 D2 D2.5 D3 D3.5 D4 D4.5 D5	Layer Depth/Date: 4/19, 4/20 Comments: We found a few pockets of older (4/19) slabs that were unreactive to skiing and tests. No new wind slab hazard observed. Could exist elsewhere, tho seems isolated at best.