Avalanche Advisory: Thursday - Apr 26, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON April 28, 2018 @ 6:59 am
Avalanche Advisory published on April 26, 2018 @ 6:59 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center

Thursday thru Friday - 

Loose Wet avalanches continue to be the primary concern through the forecast period. Timing is key to avoiding Loose Wet avalanches. Plan your travels to be clear of steep slopes before the snow become unsupportive. Signs the snow is becoming increasingly saturated, loose, and potentially unstable: pinwheels or rollerballs, small wet sloughs, and deep ski or boot-top penetration are indicators that the snow is becoming increasingly unstable and Loose Wet avalanches are becoming increasingly possible.

Caution – Slide for Life conditions exist on steep slopes prior to thawing where an unarrested fall can have serious consequences. Ski and (or) boot crampons, ice axe, and helmet recommended. 

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Near Treeline

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Below Treeline
Avalanche Problem 1: Loose Wet
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Spring is firmly in place with unseasonably warm temperatures and cool nights. Overnight temperatures are struggling to fall below freezing, which is limiting the strength of the freeze and resulting in rapid thawing during the day. Upper elevations N-NE aspects are thawing for the first time and still transitioning to corn snow and are more prone to Loose Wet avlanches. Lower elevations will warm first and most, though many areas lack sufficient snow coverage to produce significant avalanche or is thin and relatively well anchored. Timing is key to avoiding Loose Wet avalanches. Plan your travels to be clear of steep slopes before the snow become unsupportive, especially in steep, complex, or vegetated terrain. Signs the snow is becoming increasingly saturated, loose, and potentially unstable: pinwheels or rollerballs, small wet sloughs, and deep ski or boot-top penetration are indicators that the snow is becoming increasingly unstable and Loose Wet avalanches are becoming increasingly possible on slopes 35 degrees and steeper.

Caution – Slide for Life conditions exist on steep slopes prior to thawing where an unarrested fall can have serious consequences. Ski and (or) boot crampons, ice axe, and helmet recommended. 

 

advisory discussion

Spring conditions are the dominant theme for the forecast period with strong daily warming and modest overnight freezes at even the highest elevations. After multiple cycles of freeze/thaw, the snowpack has mostly transitioned to classic corn conditions on all but the higher elevation shaded N-NE aspects where the snowpack is becoming wet for the first time. Once the snow has gone through several melt-freeze cycles, it is more resistant to sliding. The N-NE aspects will need to cycle through a few more melt/freeze cycles before the threat begins to decline. Good spring corn can be found at all elevations but plan for unstable conditions developing by mid-morning to mid-day, depending on aspect, elevations, and the depth of the overnight freeze. The snow tends to thaw more quickly near and around rocks and trees where Loose Wet avalanches often originate. Loose Wet avalanches  generally need slopes of 35 degrees or steeper to slide but can flow well out into low angled terrain. Plan your travels to be off of and out from under steep slopes before they thaw excessively.

 

recent observations

Rock Creek: Warming & Avalanche Activity (4/24)

Black Mountain, Red Lake Bowl > North Face (4/23)

Mammoth Crest, Blue Couloir (4/23)

Mt. Lo>Esha: Spring Conditions (4/22)

Lundy Canyon, Upper: Wet Avalanche (4/21)

Temperatures & New Snow Accumulation @ 0400
Loc                                     New”    High (Time)/Low                    
Virginia Ridge, 9409’:            0         57 (1400)/ 41 deg F., 0 hrs below freezing, 
Tioga Pass, 9972’:                0         56 (1500)/ 37 deg F., 0 hrs below freezing.
Agnew Pass, 9355’:              0         68 (1500)/ 36 deg F., 0 hrs below freezing
June Mt., 9148’:                   0         61 (1500)/ 43 deg F., 0 hrs below freezing 
Mammoth Pass, 9500’:         0          64 (1500)/ 37 deg F., 0 hrs below freezing
Sesame Plot, 9014’:             0          61 (1500)/ 40 deg F., 0 hrs below freezing
Ch. 22-MMSA, 10,067’:        0          60 (1445)/ 41 deg F., 0 hrs below freezing
Summit-MMSA, 11,053’:       0          47 (1445)/ 40 deg F., 0 hrs below freezing 
Rock Creek, 9600’:               0         58 (1400)/ 33 deg F., 0 hrs below freezing
South Lake, 9580’:               0         62 (1500)/ 35 deg F., 0 hrs below freezing 
Sawmill, 10,200’:                  0         55 (1300)/ 31 deg F., 2 hrs below freezing

 

Weather and CURRENT CONDITIONS
weather summary

Thurs thru Sat- A trough axis will swing to near the northern California coast by Friday morning, bringing increasing divergence (broad-scale lift) aloft later today and tonight. The highest chance for showers and thunderstorms today was shifted a bit north and east to near and east of the Highway 395 corridor by evening. Friday, a solid dry slot will move over the region bring dry conditions to most areas. Widespread winds of 15-25 mph with gusts 30-40 mph can be expected for much of the region. Saturday, the upper low moves into northeast CA . Winds will kick up again with gusts 25-30 mph for many areas between mid-afternoon and early evening.

Sunday and Beyond- A closed low will be centered over Oregon on Sunday with a shortwave digging into northern Nevada Sunday afternoon with a broad-scale trough and moisture present over the western CONUS, but it’s too stable for thunderstorm development. A final shortwave drops into the trough Tuesday, quickly dropping south into the Desert Southwest. This could bring a few showers to the region on Tuesday, with thunderstorms possible in the afternoon closer to the core of the low. High temperatures will only be in the 30s and 40s in the mountains. Snow or pellets could fall as low as 5500-6000 feet in the overnight and early morning hours with snow levels around 6500-7500 feet during the day. Ridging begins to build into the West for the middle into the end of the week bringing a warming and drying trend. Temperatures will likely return to above normal Wednesday, continuing to warm into the end of the week. 

 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Thursday Thursday Night Friday
Weather: Partly cloudy. Isolated showers and thunderstorms in the afternoon. Partly cloudy then becoming clear. Isolated showers and thunderstorms in the evening. Sunny.
Temperatures: 59 to 67 deg. F. 36 to 41 deg. F. 49 to 59 deg. F.
Mid Slope Winds: Light winds becoming southeast Southwest Southwest
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Thursday Thursday Night Friday
Weather: Partly cloudy. Isolated showers and thunderstorms in the afternoon. Partly cloudy then becoming clear. Sunny.
Temperatures: 50 to 56 deg. F. 30 to 36 deg. F. 39 to 47 deg. F.
Ridge Top Winds: South to southeast South 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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