Avalanche Advisory: Saturday - Apr 14, 2018

THIS AVALANCHE ADVISORY EXPIRED ON April 17, 2018 @ 7:00 am
Avalanche Advisory published on April 14, 2018 @ 7:00 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center

Saturday – Isolated Loose Wet and Wind Slabs are the avalanche problems for the day. The recent 2 to 4” (~5 to ~10cm) of new snow from 4/12 and moderate to strong SW > NE has formed shallow stubborn Wind Slabs near and above treeline (~9000’ and above) on most aspects but Westerly aspects. Natural Wind Slabs avalanches are unlikely, small shallow triggered Wind Slabs avalanches are possible, especially in steep or complex terrain. Though likely small and isolated in nature, they can carry a rider into hazardous terrain if caught. Temperatures continue to climb Saturday, with 40’s to upper 50’s forecasted for 10,000’ and below, which will warm the surface snow and increase the potential for shallow Loose Wet avalanches primarily on E-S-W aspects Saturday with the trend decreasing on Sunday and Monday as temps cool and cloud cover increases. Very small natural Loose Wet avalanches are possible on steep solar aspects; isolated triggered releases are possible in steep or complex terrain. Rollerballs, small wet sluffs, or boot-top snow penetration are signs to move off to shaded or lower-angle slopes. Extra caution near rocky outcrops and vegetated slopes more heat is retained in the snow.  

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Above Treeline

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Near Treeline

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Below Treeline
Avalanche Problem 1: Loose Wet
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Saturday - temperatures will continue to rebound and warm the surface snow quickly with the potential for Loose Wet avalanches rising on E-S-W aspects, primarily from treeline and below (~10500”), possibly creeping higher. Small natual Loose Wet avalanches are possible, triggered releases are possible Saturday, especially in steep or complex terrain. 

Sunday thru Monday - temperatures are forecasted to cool somewhat ahead of an approach storm system, which will decrease the potential for Loose Wet avalanches during the day and confine the problem to primarily on E-S-W aspects, below ~10,000’. Signs of wet snow instabilities include: pinwheels, rollerballs, deep ski or boot penetration, and point releases. Loose Wet avalanches can trigger larger deeper releases, especially in the lower elevations (~10000’ and below). Very small natural avalanches are possible, triggered releases possible, especially in sheltered, steep, or rocky terrain. 

Avalanche Problem 2: Wind Slab
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The recent fast moving storm system that passed through the region 4/12 deposited 2” to 4” of new snow and was accompanied by strong SW winds, which the swung around to the NW to NE as the system moved off to the east. Due to the wide swings in wind direction as the sytem passed through the region, shallow Wind Slabs formed near above treeline (~9000’ and above) in gullies, depressions, and near rock outcrops on NW-NE-SE-SW aspects. Southwest winds will increase Sunday in advance of the next storm system but will have little transportable snow to form new Wind Slabs, except possibly in the highest elevations. Saturday, natural Wind Slab are unlikely, isolated triggered releases are possible, especially in steep or complex terrain near treeline and above (~9000’ and above). Triggered releases are most likely in areas that favor drifting (rock outcrops, gullies, leeward side of corniced ridges, etc.) Use additional caution in and around terrain features that promote drifting, under cornices, tops of chutes, and gully sidewalls. 

advisory discussion

The recent new snow has settled and bonded well to the underlying snow surface. Warm temperatures over the past couple of days has formed a light melt freeze crust on all slopes that receive direct sunlight but NNW-NE aspects where dry shallow soft condition over a firm melt/freeze base exists. Solar aspects thawed slightly during the day Friday with only the surface ~5 cm to ~10 cm becoming moist or wet while the melt/freeze crust (20 to 30 cm. 8”-12” thick) below remained dry. Under the melt/freeze crust, is moist grains for an additional 20 to 40 cm (8’ to 16”), which rests on a very hard mid-pack. The storm that passed through the region (4/11) left 2” to 4” of new snow in it’s wake from Mammoth north. The new snow was accompanied by strong SW winds which formed Wind Slabs above ~9000 on NW-NE-SE aspects. Tests Friday suggest the recently formed Wind Slabs are isolated, shallow and stubborn, primarily a concern in steep or complex terrain. Generally, the new snow is shallow in nature and has bonded well to the pevious snow surface. 

Loose Wet avalanche concerns is a concern in the mid and lower elevations (10,500’ and lower) for Saturday, primarily E-S-W aspects, decreasing Sunday and Monday as increased cloud cover and cooler temperatures settle in. 

 

 

recent observations
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Red Cone > Crystal Lake > TJ Bowl (4/13)

Little Lakes Valley, Rock Creek (4/13)

Red Cone (4/11)

Mount Wood (4/11)

Mono Pass Tour (4/10)

Spring Conditions In Valentine Cirque (4/9)

Temperatures @ 0400

Loc                                          New    Highs/Lows                                            

Virginia Ridge, 9409’:             0         42/31 deg F., 8 hrs below freezing, 
Tioga Pass, 9972’:                 N/A     36/25 deg F., >5 hrs below freezing.
Agnew Pass, 9355’:               0         47/25 deg F., 9 hrs below freezing
June Mt., 9148’:                    0         41/33 deg F., 7 hrs below freezing 8pm-3am
Mammoth Pass, 9500’:           N/A     49/29 deg F., 8 hrs below freezing
Sesame Plot, 9014’:               0         44/35 deg F., 6 hrs below freezing
Ch. 22-MMSA, 10,067’:                     48/32 deg F., 3 hrs below freezing
Summit-MMSA, 11,053’:                   29/26 deg F., 24 hrs below freezing
Rock Creek, 9600’:                N/A     42/28 deg F., 7 hrs below freezing
South Lake, 9580’:                           N/A     50/27 deg F., 10 hrs below freezing

Sawmill, 10,200’:                   0         40/29 deg F., 10 hrs below freezing

 

Weather and CURRENT CONDITIONS
weather summary

...WIND ADVISORY IN EFFECT FROM 2 PM SUNDAY TO 2 AM PDT MONDAY...

Saturday– temperatures will warm to near mid 40s-near 50 for Sierra. A late day zephyr-type breeze is expected with gusts 25-30 mph.         

Sunday- the thermal and pressure gradients will tighten up during the day with most locations seeing windy conditions ahead of the cold front. Wind gusts 45-55 mph are likely Sunday afternoon and evening, with stronger gusts up to 70 mph possible in wind prone areas along US-395 in Mono County. Sierra ridge gusts of     80+ mph are also likely. The stronger winds could extend into the late night hours for Mono. As the storm and cold front move inland, rain and snow will push south into Mono county late Sunday evening with the moisture band and forcing losing some of its punch, leading to lesser snow amounts. 

Monday- a secondary shortwave will keep clouds and snow showers over the higher elevations. Unstable conditions with a cold pool aloft could produce isolated thunder and snow pellets/graupel. Snow showers could continue into Monday night, with isolated light accumulations possible. 

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Saturday Saturday Night Sunday
Weather: Sunny Partly cloudy then becoming mostly cloudy. Partly cloudy.
Temperatures: 49 to 57 deg. F. 29 to 34 deg. F. 44 to 54 deg. F.
Mid Slope Winds: Light Winds. Southwest Southwest
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Saturday Saturday Night Sunday
Weather: Sunny. Partly cloudy then becoming mostly cloudy. Mostly cloudy then becoming partly cloudy.
Temperatures: 44 to 50 deg. F. 24 to 29 deg. F. 36 to 44 deg. F.
Ridge Top Winds: Southwest Southwest Southwest
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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