Avalanche Advisory: Friday - Mar 13, 2020

THIS AVALANCHE ADVISORY EXPIRED ON March 14, 2020 @ 6:52 am
Avalanche Advisory published on March 13, 2020 @ 6:52 am
Issued by Chris Engelhardt - Eastern Sierra Avalanche Center

MODERATE avalanche danger exists at UPPER Elevations Friday for heightened hazard for WIND SLAB on ALL ASPECTS. LOW avalanche danger will continue near and below treeline. Winds are predicted to switch from light to moderate NE flow to much stronger W-SW orientation. In areas that saw substantially more new snow mid-week (Southern part of the forecast zone & Mammoth Lakes Basin), this wind shift will redistribute low-density snow and cross-load alpine terrain, such as couloirs, slopes adjacent to ridgelines, cliff bands and rock outcroppings.

2. Moderate

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

1. Low

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

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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Be on the lookout for pockets of unstable, shallow wind slab on specific terrain features such as slopes adjacent to rock outcropping, cliff bands and side walls of gullies and chutes. ALL ASPECTS in the Upper Elevations should be taken into account with recent Northerly winds switching to the W-SW and increasing in velocity as the day progresses. Field observations in the upper elevations yesterday found upwards of 15-20cm of new snow in the southern part of the range (SF Big Pine & Kearsage Area) and skiers in the Mammoth Lakes Basin reported much deeper new snow conditions than initially reported, some reactive shallow wind slab, and visible snow transport taking place during the day. This more accurate knowledge of deeper low-density, new snow amounts, combined with increasing W-SW winds should be considered in relation to potential for fresh wind slab development. Be observant for blowing snow, recent loose snow avalanche activity, and fresh cross loaded ribbons and pillows of snow established on terrain features conducive to capturing snow. Shooting cracks or panels of firmer wind effected snow resting on top of looser, less cohesive snow will be good indicators that wind slab is present. Be observant of overhead hazards, and plan your route accordingly if you’re travelling in tight and confined terrain where small slides and spindrift originating in the alpine could be an issue if snow funnels in your direction. Anticipate that warming from the sun could loosen freshly deposited small panels of snow from sunny aspects today.

Avalanche Problem 2: Loose Wet
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Warm temperatures and sunny skies today along with light NW winds in the early part of the day will play a part in allowing Sunny aspects to heat up and loosen. Pay attention for small loose wet activity on E-SE-S-SW-W aspects. New point release activity, fresh Roller balls and pin-wheeling of snow are all indicators of warming and loosening of residing snow. Pay particular attention if you’re attempting routes that are affected from terrain above that is getting significantly warmed from the sun. Be observant for even small amounts of moving snow or rock fall that could impact you from above, especially if in tight or confined terrain that is exposed to overhead hazards.

recent observations
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3/12- Mammoth Area –TJ Bowl –small skier triggered avalanche

3/12 – SF Big Pine – 15-20cm new snow

3/12 – Onion Valley– University pass -20-25cm new snow

3/12 - Mammoth Area - Warming on Solar aspects

3/12- Mammoth Area –Red Cone -minor wind loading

3/11 – June Lake Area –New snow in Negatives- snow conditions

 

Weather and CURRENT CONDITIONS
weather summary

Sunny weather for Friday with continued warm temperatures reaching 50F for lower mountain elevations and 31-39F above 10000ft. Light to moderate NW winds will transition to a W-SW flow this afternoon with velocities in the 25-35mph range with ridge top gusts in the high country up to 65mph. Winds will continue to increase to extreme levels tonight with gusts in the 80mph range as this weekend’s storm moves into the area. Upwards of 2” of new snow could fall tonight at the onset of the storm. Heaviest accumulations of snow associated with this storm are predicted for the Lake Tahoe area with Mono County potentially seeing 1ft along the Sierra crest. It will be interesting to see what happens.

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. Snow levels below 7000 feet increasing to 8000 feet in the afternoon. Chance of precipitation is 5%. Clear then becoming partly cloudy. Chance of snow. Snow levels 7500 feet decreasing to below 7000 feet after midnight. Chance of precipitation is 25%. Sunny. Chance of snow through the day. Snow levels below 7000 feet. Chance of precipitation is 30%.
Temperatures: 40 to 50. deg. F. 25 to 31. deg. F. 31 to 41. deg. F.
Mid Slope Winds: Light winds becoming southwest 15 to 25 mph with gusts to 50 mph in the afternoon. Southwest 15 to 30 mph with gusts to 70 mph. Southwest 25 to 35 mph with gusts to 70 mph.
Expected snowfall: No accumulation. 90% probability no accumulation. | SWE = none. in. up to 2 inches. | SWE = less than 0.10 inch. in. 1 to 3 inches. | SWE = up to 0.15 inch. in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: Sunny. Snow levels below 7000 feet increasing to 8000 feet in the afternoon. Chance of precipitation is 10%. Partly cloudy. Chance of snow through the night. Snow levels 7500 feet decreasing to below 7000 feet after midnight. Chance of precipitation is 30%. Partly cloudy. Chance of snow through the day. Snow levels below 7000 feet. Chance of precipitation is 35%.
Temperatures: 31 to 39. deg. F. 19 to 24. deg. F. 22 to 30. deg. F.
Ridge Top Winds: Northwest 15 to 30 mph with gusts to 45 mph shifting to the southwest 25 to 35 mph with gusts to 65 mph in the afternoon. Southwest 30 to 45 mph increasing to 35 to 55 mph after midnight. Gusts up to 80 mph. Southwest 35 to 55 mph with gusts to 80 mph.
Expected snowfall: No accumulation. | SWE = none. in. up to 2 inches. | SWE = less than 0.10 inch. in. up to 3 inches. | SWE = up to 0.15 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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