Avalanche Advisory: Wednesday - Feb 20, 2019

THIS AVALANCHE ADVISORY EXPIRED ON February 21, 2019 @ 6:58 am
Avalanche Advisory published on February 20, 2019 @ 6:58 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

MODERATE avalanche danger in the form of WIND SLABS exists at upper and mid elevations on all aspects due to increasing and shifting winds, and possible light new snow this afternoon.  Human triggered wind slab avalanches are possible in exposed areas. LOOSE DRY sloughs are also a concern in low elevation steep sheltered terrain.

2. Moderate

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

2. Moderate

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

1. Low

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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
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Northerly winds yesterday intensified as they shifted out of the south and west late last night with gusts into the 40mph range even at lower elevations. Greatest concern will be for fresh smooth wind-loaded pockets from today’s W to SW winds, but recognize older wind deposits that could now looked etched away could still be sensitive as well. Below ridgelines, the sidewalls of gullies, and around mid-slope terrain fluctuations that catch snow are likely spots to find denser sensitive wind-deposits. Areas that receive several inches plus of new low-density snowfall this afternoon and tonight will become even more concerning. While likely to be relatively small, these wind slab avalanches could knock a person off their feet and lead to a nasty fall in consequential terrain and even a burial if a terrain trap is involved.

Avalanche Problem 2: Loose Dry
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Cold temperatures have kept snow soft and loose in sheltered areas. Several reports of sizeable loose-dry sloughs were reported yesterday in steep terrain. These sloughs could be large enough to knock someone off their feet and even end in a burial if a terrain trap is involved. Shallowly buried rain crusts at low elevations will make it even easier for loose snow to slide. Manage slough wisely, or avoid steep sheltered terrain.

Avalanche Problem 3: Cornice
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CORNICES have become established on EASTERLY and NORTHERLY aspects throughout the range. Give these curling wavelike features a wide berth and make sure you are well on terra firma on the windward side of ridges where cornices reside. Cornice fall not only is hazardous if it gives way beneath you, but can affect travelers if it falls from above when you are travelling on slopes below. Cornice fall can be the big trigger that start avalanches on slopes below as the falling blocks can be of tremendous weight and scale. Cold temps help to keep these locked up, but with forecasted SUNNY SKIES today be cognizant that solar gain can contribute to loosening freshly formed cornices and other teetering wind deposited formations in alpine terrain--particularly easterly aspects. Cornices are one of the main contributors of fatalities for seasoned guides, skiers, and mountaineers in the alpine environment. Always give cornices extra space, as they can release further back on ridges than expected due to the connectivity of the snow.

advisory discussion

Rain over Valentine’s day led to firm icy crusts up to around 10,000’+, which were then covered by additional snowfall. In wind swept areas and at lower elevations where these icy crusts are at the surface or only shallowly buried, slide for life conditions could exist. Especially with cold temperatures, it will be important to monitor how the layers of snow directly below and above these crusts change, particularly with an eye for weak faceted snow formation.

recent observations
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-2/19 - June Area - Negatives & Carson Bowl: Small isolated human triggered wind slabs.  Reports of loose-dry sloughing in Hemlock Ridge.

-2/19 - McGee Creek - Esha Canyon: Wind effects, wind slab.

-2/19 - Mammoth - Red Cone and Lake George Headwall: Loose sloughing, isolated wind slab pockets.

 

Weather and CURRENT CONDITIONS
weather summary

Light snow showers are likely this afternoon thru tomorrow as another even colder low-pressure system enters our area. Up to 2” of very low-density snow is expected today, with a few more inches tonight, and a couple more tomorrow. Slightly more is possible around Mammoth, and due to Mono lake effect even more around the June area. Winds have intensified and shifted out of the SW and W late last night, with gusts into the 40s even at low elevations. These winds should decrease slightly in the afternoon; shift out of the NW tonight; and then out of the N for tomorrow. Drier conditions with slightly warmer temperatures are looking likely from Friday thru early next week.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Widespread snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 70%. Cloudy. Widespread snow showers in the evening, then scattered snow showers after midnight. Snow levels below 7000 feet. Chance of precipitation is 80%. Mostly cloudy. Chance of snow showers. Snow levels below 7000 feet. Chance of precipitation is 55%.
Temperatures: 18 to 24. deg. F. 5 to 10. deg. F. 12 to 22. deg. F.
Mid Slope Winds: Southwest around 15 mph. Gusts up to 45 mph decreasing to 30 mph in the afternoon. Northwest around 15 mph with gusts to 30 mph. North 15 to 25 mph with gusts to 35 mph.
Expected snowfall: 90% probability up to 2 inches. 10% probability of 2 to 4 inches. | SWE = less than 0.10 inch. in. 80% probability of 1 to 4 inches. 20% probability of 4 to 6 inches. | SWE = less than 0.10 inch. in. Up to 2 inches. | SWE = less than 0.10 inch. in.
Over 10,000 ft.
Wednesday Wednesday Night Thursday
Weather: Mostly cloudy. Widespread snow showers in the afternoon. Snow levels below 7000 feet. Chance of precipitation is 85%. Cloudy. Widespread snow showers in the evening, then scattered snow showers after midnight. Snow levels below 7000 feet. Chance of precipitation is 80%. Mostly cloudy. Snow showers likely. Snow levels below 7000 feet. Chance of precipitation is 55%.
Temperatures: 10 to 15. deg. F. 2 below to 4 above zero. deg. F. 2 to 7. deg. F.
Ridge Top Winds: West 25 to 35 mph with gusts to 55 mph shifting to the southwest 15 to 30 mph with gusts to 40 mph in the afternoon. Northwest 15 to 25 mph with gusts to 40 mph. North 15 to 30 mph with gusts to 45 mph.
Expected snowfall: 90% probability up to 2 inches. 10% probability of 2 to 4 inches. | SWE = less than 0.10 inch. in. 80% probability of 1 to 4 inches. 20% probability of 4 to 6 inches. | SWE = up to 0.20 inch. in. Up to 2 inches. | SWE = less than 0.10 inch. 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.

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