Eastern Sierra Avalanche Advisory - 3/19/17

THIS AVALANCHE ADVISORY EXPIRED ON March 20, 2017 @ 6:46 am
Avalanche Advisory published on March 19, 2017 @ 6:46 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center

Spring like conditions will continue to dominate Sunday with the surface snow warming through the day (Easterly > Southerly > Westerly), natural and human triggered small loose wet avalanches possible as the snow surface softens. An approaching storm system increased cloud cover overnight, which limited the depth of the freeze overnight, and with moderate to strong SW winds today which will likely slow surface snow thawing in the mid to upper elevations.  Caution - small wet slides are dense/heavy and are capable of carrying a rider into hazardous terrain or possibly entrain enough snow to bury a person, especially if a terrain trap is involved.  Early starts are recommended before the snow become saturated and unsupportable.  Caution – Cornices can fail unexpectedly, avoid Corniced slopes and give them wide berth while traveling along ridgelines. Possible “Slide for Life” conditions exists in the AM before the snow surface thaws. Evaluate snow and terrain carefully. 

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Avalanche Problem 1: Loose Wet
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Natural and human triggered small loose wet avalanches will become increasingly possible as the snow surface thaws and becomes wet during the day. An approaching storm system will increase cloud cover with accompanying moderate to strong SW winds will reduce and slow surface snow thawing in the mid and upper elevations.  Cloudy skies overnight has kept temperatures warm & mild overnight, which has produced a weak freeze with the surface snow likely becoming unsupportable fairly quickly. The surface snow will warm through the day (Easterly > Southerly > Westerly), increasing near cliffs and rock outcrops. Natural and human triggered small loose wet avalanches possible as the snow surface softens. Large pinwheels or snow penetration boot top or greater are signs the snow is loosing strength and becoming unstable, steep terrain on these aspects should be avoided.  

A number of factors affect the rate of snow thawing: Aspect (Easterly facing slopes begin to thaw first, followed by south and then west in the afternoon); Elevation: lower elevations warm more quickly than higher elevation, Cloud cover: cloud cover can shade the slopes slowing thawing. However, clouds can help to slow or limit overnight cooling limiting how solid the snow sets-up, Air temperature: Warmer air temperatures leads to more snowpack warming.  

advisory discussion

Spring has made its annual appearance with two weeks of above average temperatures and for the most part sunny skies. The last snowfall recorded in the region was on March 5th with up to 7” primarily in the June and Mammoth basins, which was followed by strong winds producing highly wind-effected and firm snow conditions in the upper elevations. Prior to this temperatures were slightly cooler than seasonable with a winter like snowpack. As temperatures began to climb the snowpack began to transition to a spring snowpack with melt freeze crusts forming at the surface while the snowpack as a whole consolidated and strengthened. With the arrival of warming temperatures, Loose Wet avalanches were observed in the Low to Mid elevations, slowly creeping into the upper elevations as temperatures continued to climb into unseasonably warm territory this last week. A change in the weather is forecasted for Monday night when winter will reassert itself through the upcoming week. Slide For Life conditions may exist on slopes before they thaw or areas with hard smooth wind board.  Crampons, ice axes, whippets, recommend may be required to safely travel in steeper terrain. Caution – Cornices can fail unexpectedly, avoid Corniced slopes and give them wide berth while traveling along ridgelines.

Saturday High / Overnight Low Air Temperatures in Degrees F as of 0600;
                                                 Low    High
Virginia Lakes (9300’):                32     48
Ellery Lake (9545’):                    33     46
Agnew Pass (9450’):                  35     48
June Mtn Wx Plot (9220’):          35     47
Sesame Snow Study (9014’):      36     48
Rock Creek (9700’):                   23     49
South Lake (9600’):                   32     50

 

 

recent observations
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3/16 Negatives, June Lake, Spot Weather Obs

3/16 Mt. Tom - SE Gully - Snow Softening

3/16 Mt. Tom SE Chute

Weather and CURRENT CONDITIONS
weather summary

Sunday - Moist southwest flow and a jet streak over northwest Nevada will keep a slight chance of showers in the forecast today with mostly cloudy skies and gusty ridge winds. Any showers that do form today will be light with QPF measured in hundredths. 

Monday thru Tuesday – Monday a brief drying trend with an increasing southerly surface winds as gradients begin to tighten in response to the incoming trough. Wind gusts of 25 to 35 mph with ridge gusts around 70 mph can be expected. The negatively tilted trough approaching the coast will allow southerly flow over the region with warm air advecting in from the south. Precipitation begins to increase Monday night in the Sierra as moisture begins to bank up against the mountains. The heaviest precipitation is expected Tuesday morning through Tuesday afternoon. Recent trend in the models has continued to enhance the southerly flow, which will keep snow levels higher through the main precipitation event on Tuesday. Precipitation amounts are still expected to be in the 1-2" (SWE) range along the Sierra. With warmer southerly flow snow levels are forecast to be in the 7000-7500 foot range during the heaviest precipitation. Snow levels are expected to drop Tuesday night with precipitation rates dropping off. 
 
Wednesday - another short wave is expected to move through the region with organized bands of convective showers. Snow levels between 5000-5500 feet, lower at times. General accumulations would be light with locally heavier convective showers, snow pellets can accumulate quickly a quick inch or two. The showers will wind down Wednesday evening behind the short wave and warmer temps aloft move in. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Slight chance of showers in the afternoon. Mostly cloudy. Slight chance of snow showers in the evening. Slight chance of showers after midnight. Cloudy. Slight chance of snow showers.
Temperatures: 46 to 54 deg. F. 26 to 32 deg. F. 44 to 52 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 15 to 20 mph with gusts to 40 mph. 15 to 20 mph with gusts to 35 mph. 15 to 25 mph with gusts to 45 mph.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Sunday Sunday Night Monday
Weather: Mostly cloudy. Slight chance of snow showers in the afternoon. Mostly cloudy. Slight chance of snow showers after midnight. Mostly cloudy. Slight chance of snow showers.
Temperatures: 40 to 48 deg. F. 21 to 26 deg. F. 35 to 43 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 30 to 45 mph decreasing to 25 to 35 mph in the afternoon. Gusts up to 80 mph. 25 to 35 mph. Gusts up to 85 mph decreasing to 70 mph after midnight. 25 to 35 mph with gusts to 65 mph.
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 Snowpack Summary is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

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