Pro Field Report

Basic Information

Observation Date:

December 14, 2020

Submitted:

December 15, 2020

Observer:

SAC - VandenBos

Zone or Region:

Sawtooth and Western Smoky Mtns

Location:

Salmon River Headwaters (7,300-10,000, primarily NE-N-NW-W-SW)

Recent Avalanches?

None Observed

Cracking?

Isolated

Collapsing?

None Experienced

Isolated cracking in thin, freshly deposited wind drifts at upper elevations.

Stability Rating:

Good

Confidence in Rating:

Moderate

Stability Trend:

Steady

Continue to be in the very weak snowpack without a slab waiting game. New snow and wind hadn't significantly affected stability, but the presence of this snow will likely make the 12/11 and 12/13 interfaces even more touchy when they get a proper load.

Advanced Information

Cloud Cover:

Mostly Cloudy

Temperature:

upper teens to low 20s F (estimated)

Wind:

Moderate , NE

Somewhat windier than forecast in the afternoon, with brief flurries of S-1 precipitation for a trace of accumulation. Light to moderate winds blowing out of the N-NE along ridgetops. Periodic light winds sifting snow around down to valley bottom. Quite a bit of incoming solar earlier in the day, increasing clouds in the afternoon and clearing into the evening.

New snow: 1 cm of new snow from 12/11 squalls, 4-5 cm in past 24 at upper elevations. I went out trying to find wind affected snow where I thought it would be at its worst. Encountered isolated fresh drifts up to 20 cm thick (max), which extended down from ridge tops for 1-2 m. These small, dinner table-sized drifts were resting on a variety of surfaces and were stubborn to unreactive.

Old snow: Continue to be impressed/concerned with the snowpack that is developing, particularly below the inversion line of ~8,500'. As noted further north in the Sawtooths, a period of warm air and sunshine last week allowed crusts to wrap around quite a bit further north than during the previous few weeks, creating a 1-5cm thick crust built out of what were once advanced facets. Quite neat to look at if you like snow, not so much if you are hoping for good stability. Today, I encountered this crusts on slopes that faced 30 degrees north of west (300), even at slope angles down into the low 20s. Sandwhiched between this crust and the 11/17 rain crust is a F- stack of 1-3 mm facets. Truly impressive how advanced this faceting has become, with striations common in large grained crystals. Could probably give someone a handful and convince them they were looking at DH... On top of the upper crust, the 1 cm that fell on 12/11 has faceted somewhat (based on behavior, not seen with scope). Plenty of shortwave coming in today but light winds kept surfaces cool and it is clear out as of 4AM (12/15), I anticipate that 12/13-14 snowfall has faceted appreciably as well now. HS=50-60cm along valley bottoms. Did not go looking for pre 11/7 snow today.

Continue to close steep, open terrain where October snow exists. Had steep terrain where wind slabs existed closed but did not encounter.