Avalanche Advisory: Monday - Apr 16, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON April 17, 2018 @ 6:53 am
Avalanche Advisory published on April 16, 2018 @ 6:53 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center

Monday – Changeable spring weather is requiring a change in the avalanche forecast with Wind Slabs the avalanche problem for the day. A quick moving spring storm has moved through the region overnight with SW winds in excess of 50 MPH with  2” to 4” (~5 to ~10cm) of new snow as of 400 AM, up to 6” possible in the upper elevations with an additional 1” to 5” forecasted during the day. This has likely formed Wind Slabs on NW-NE-SE aspects near and above treeline (~10,000’+/- and above). Natural Wind Slabs avalanches are possible, triggered Wind Slabs avalanches are likely, especially in steep or complex terrain. 

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Near Treeline

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Below Treeline
Avalanche Problem 1: Wind Slab
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A quick moving spring storm has moved through the region overnight with SW winds in excess of 50 MPH and 2” to 4” (~5 to ~10cm) of new snow as of 400 AM, with up to 6” possible in the upper elevations with an additional 1” to 5” of snow possible during the day. This has likely formed tender Wind Slabs on NW-NE-SE aspects near and above treeline (~10,000’ and above). Natural Wind Slabs avalanches are possible, triggered Wind Slabs avalanches are likely, especially in steep or complex terrain. Anticipate Wind Slabs forming near above treeline (~10,000’ and above) in gullies, depressions, and near rock outcrops. Strong Southwest winds (30 to 40 MPH) are forecasted to continue through much of the day in the upper elevations (~10,000’ an above), which will maintain the Wind Slabs avalanche threat through the day, easing somewhat tonight as winds ease and swing to the West. This will allow the newly formed Wind Slabs to begin bonding to the underlying snow and begin strengthening. Natural Wind Slab avalanches are possible, especially in steep or complex terrain near and above treeline (~10,000’+/- and above). Triggered releases are likely in areas that favor drifting (rock outcrops, gullies, leeward side of ridges, etc.) Use additional caution in and around terrain features that promote drifting, under cornices, tops of chutes, and gully sidewalls. 

advisory discussion

A spring storm that was due to brush by the region has dug further south than originally forecasted, bringing a welcomed shot of moisture to the eastern Sierra. However, this has altered the avalanche problems and required an update to reflect the current avalanche problem. The storm moved into the region Sunday afternoon with strong SW winds and snow beginning after dark. Snow continued off and on through the night with steady SW winds of 50 to 60MPH reported on Mammoth Mountain. Strong Southwest winds (30 to 40 MPH) are forecasted to continue through much of the day in the upper elevations (~10,000’ +/-, and above) with an additional 1" to 5" of new snow, which will maintain the Wind Slab avalanche threat through the day on NW-NE-SE aspects, easing somewhat tonight as winds decrease to 15 to 20MPH and swing to the West. This will slow Wind Slab formation and allow recently formed Wind Slabs to begin bonding to the underlying snow and strengthening. Natural Wind Slab avalanches are possible, especially in steep or complex terrain near and above treeline (~10,000’+/- and above). Triggered releases are likely, especially in areas that favor drifting (rock outcrops, gullies, leeward side of ridges, etc).

 

 

 

recent observations

Bishop Creek: Rain Effect (4/15)

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

Little Lakes Valley, Rock Creek (4/13)

Red Cone (4/11)

Mount Wood (4/11)

Temperatures & New Snow @ 0400
Loc                                     New”    Highs/Lows                    
Virginia Ridge, 9409’:           ~3”      45/25 deg F., 6 hrs below freezing, 
Tioga Pass, 9972’:               N/A      41/19 deg F., 10 hrs below freezing.
Agnew Pass, 9355’:             ~2”      44/24 deg F., 7 hrs below freezing
June Mt., 9148’:                  ~4”      44/23 deg F., 7 hrs below freezing 
Mammoth Pass, 9500’:         N/A     47/22 deg F., 7 hrs below freezing
Sesame Plot, 9014’:             ~2”     44/23 deg F., 6 hrs below freezing
Ch. 22-MMSA, 10,067’:                   35/19 deg F., 12 hrs below freezing
Summit-MMSA, 11,053’:                  31/16 deg F., 24 hrs below freezing
Rock Creek, 9600’:              ~3”      44/25 deg F., 6.5 hrs below freezing
South Lake, 9580’:              N/A      47/24 deg F., 6 hrs below freezing 
Sawmill, 10,200’:                ~2        42/21 deg F., 9 hrs below freezing

 

Weather and CURRENT CONDITIONS
weather summary

Monday- The main area of snow over the Sierra has transitioned since midnight to bands of snow showers, which should continue through mid-morning. This afternoon and evening, chilly conditions and brisk winds (gusts mainly 30-35 mph) with bands of snow showers redeveloping due to unstable conditions and secondary shortwave passage. The stronger wave is projected to swing into Mono County, with potential for heavier snow shower bands extending east of the crest (originating from thunderstorms forming west of the Sierra) with portions of western Mono County receiving a few inches of snowfall. Later tonight, snow showers are expected to diminish, with chilly conditions prevailing as temperatures drop into the 20s for    most lower elevations and teens for Sierras. 

Tuesday- dry conditions with lighter winds will prevail with some warming into the upper 20s to low 40s the Sierra ( about 10 degrees below average). Tuesday night cloud cover increases ahead of the next storm system. 

Wednesday thru Friday- models have come into good alignment in the early part of the extended but start to diverge toward the end of the forecast. The GEFS ensemble members are mainly trending toward the EC/GFS solutions, though there could be shifts in the track of any upper low that moves into the region with the upper level low splitting and diving farther south as it moves inland. Precipitation to develop Wednesday afternoon in eastern California but the track farther south means a little less QPF for the bulk of the area with the highest amounts in the Sweetwater Range and the White Mountains in Mono County with up to 6 inches are possible above 9000 feet. The upper low moves east Thursday afternoon and evening. Below normal temperatures are likely through Thursday. Short wave ridging builds for Friday with highs warming to near normal. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Monday Monday Night Tuesday
Weather: Cloudy. Widespread snow showers. Mostly cloudy. Scattered snow showers. Sunny.
Temperatures: 24 to 32 deg. F. 11 to 17 deg. F. 34 to 42 deg. F.
Mid Slope Winds: Southwest West Light winds.
Expected snowfall: 2 to 4" in. up to 2 in. 0 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Cloudy. Widespread snow showers. Mostly cloudy. Widespread snow showers in the evening, then scattered snow showers after midnight. Sunny.
Temperatures: 16 to 23 deg. F. 6 to 11 deg. F. 28 to 33 deg. F.
Ridge Top Winds: Southwest West Northwest
Expected snowfall: 2 to 5 in. up to 2 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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