Avalanche Advisory: Friday - Jan 1, 2021 | Eastern Sierra Avalanche Center

THIS AVALANCHE ADVISORY EXPIRED ON January 2, 2021 @ 6:40 am
Avalanche Advisory published on January 1, 2021 @ 6:40 am

Issued by Steve Mace - ESAC

Bottom Line

MODERATE avalanche danger exists today near and above treeline while LOW danger persists at lower elevations. Wind slabs will be the primary concern on all aspects near and above treeline. These wind slabs will range in both size and sensitivity, from fresh and sensitive to older and more stubborn. Evaluate snow and terrain carefully if you head into the backcountry today and be wary of the very thin obstacle-ridden conditions.

2. Moderate

Above Treeline

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

Near Treeline

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

Below Treeline

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Avalanche Problem 1: Wind Slab

Type ?
Aspect/Elevation ?
Likelihood ?

Certain

Very Likely

Likely

Possible

Unlikely
Size ?

Historic

Very Large

Large

Small

In true Sierra fashion, we have seen strong winds shift from one end of the compass rose to the other and back again over the past couple of days. Wind slabs will range in both size and sensitivity today from fresh and sensitive to older and more stubborn and will be possible to find on ALL aspects. Be particularly warry on more easterly, southerly and westerly terrain today as strong ridgetop winds will continue out of the N-NW. Exposed areas and leeward catchment zones near and above treeline deserve elevated caution. Large drifts, hollow drum-like snow, recent cornice growth, and uneven snow surfaces are all clues that indicate nearby wind deposits. Do your own localized assessments and be suspect of terrain features that encourage drifting such as the leeward sides of ridgelines, gully features, and cross-loaded depressions.

advisory discussion

After many long discussions, the forecasters have decided to drop the persistent slab as a problem. While field observations continue to report a very poor snowpack structure throughout the northern part of the forecast area, we have just not seen any activity on these weak faceted layers near the ground. In addition, our very thin snowpack continues to degrade throughout the pack, remaining for the most part unconsolidated and limiting the available “Slab”. From a 10,000’ view our snowpack is riddled with wide swaths of bare ground and shallow un-rideable terrain and this lack of contiguous snow coverage is greatly limiting the areas where a persistent slab avalanche might occur. This does not however mean that it is completely out of the realm of possibility for an avalanche to be triggered on these basal facets. An intrepid backcountry traveler could foreseeably find a place in our large and diverse range where the right conditions exist to trigger a consequential persistent slab avalanche, but this would be an unlikely and isolated event. Make no mistake, our weak snowpack deserves continued caution and evaluation. When in doubt, give yourself a wide safety margin, be wary of hazards that may reside above you, and use terrain choice to limit your exposure. It is very likely that a significant snowstorm, like the one predicted for early next week, will tip the balance, bring this persistent weak layer back into focus, and kick off a significant avalanche cycle.

recent observations

Submit Snowpack Observations

Submit Avalanche Observations

12/31- VA Lakes- Poor Structure, propagating test results, Sensitive Wind deposits

12/31- VA Lakes- Propagating test results

12/31- Mammoth Area- Snowpack conditions in the lakes basin

12/31- Mammoth Area- San Joaquin Ridge, Very strong winds

12/30- Mammoth Area- Snow conditions along the Mammoth crest

12/30- Mammoth Area- Weak snowpack structure in the lakes basin

12/30-Mammoth Area- Weak Structure, propagating test results in the Sherwins

12/30- Mammoth Area- Snow conditions in the lakes basin

12/30- June Area- Snow conditions on Chicken wing

Weather and CURRENT CONDITIONS

weather summary

Sunny skies are expected this morning becoming partly cloudy this afternoon. Mild temperatures are expected today with highs in the mid 30°F at upper elevations. Moderate to strong winds will continue out of the N-NW today although we may see wind speeds taper off this afternoon.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS

For 8,000 ft. to 10,000 ft.

	Friday	Friday Night	Saturday
Weather:	Sunny then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.	Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.	Mostly cloudy then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures:	34 to 40. deg. F.	18 to 23. deg. F.	30 to 38. deg. F.
Mid Slope Winds:	Light winds. Gusts up to 25 mph in the morning.	Southwest 15 to 25 mph. Gusts up to 35 mph increasing to 55 mph after midnight.	Southwest around 15 mph. Gusts up to 40 mph decreasing to 25 mph in the afternoon.
Expected snowfall:	0 in.	0 in.	0 in.

Over 10,000 ft.

	Friday	Friday Night	Saturday
Weather:	Sunny then becoming partly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.	Partly cloudy then becoming mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 0%.	Mostly cloudy. Snow levels below 7000 feet. Chance of precipitation is 5%.
Temperatures:	29 to 35. deg. F.	15 to 20. deg. F.	24 to 30. deg. F.
Ridge Top Winds:	Northwest 15 to 20 mph. Gusts up to 35 mph decreasing to 25 mph in the afternoon.	West 15 to 25 mph with gusts to 45 mph increasing to southwest 30 to 45 mph with gusts to 75 mph after midnight.	Southwest 15 to 30 mph. Gusts up to 50 mph decreasing to 35 mph in the afternoon.
Expected snowfall:	0 in.	0 in.	0 in.

Disclaimer

This Avalanche Advisory is designed to generally describe avalanche conditions where local variations always occur. This product only applies to backcountry areas located outside established ski area boundaries. The information in this Avalanche Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.