Avalanche Advisory - Tue, Jan. 10, 2017

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THIS ADVISORY EXPIRED ON January 12, 2017 @ 12:28 pm
Avalanche Advisory published on January 10, 2017 @ 12:28 pm
Issued by Doug Lewis - Eastern Sierra Avalanche Center

bottom line:
  • Blizzard warning in effect until 10 am PST Wednesday...dangerous blizzard conditions due to heavy snow and strong winds will continue today through Wednesday morning. Periods of moderate to heavy snow will continue through Wednesday night.
  • Winter storm warning in effect from 10 am Wednesday to 4 am PST Thursday. Snow accumulations through Thursday morning: 1 to 3 feet for communities along highway 395. Totals of 3 to 6 feet above 7500 feet west of highway 395 with locally higher amounts. Snow levels: all valley floors, may briefly rise to 7000 feet this afternoon and evening before falling again.
  • Winds: southwest 20 to 30 mph with gusts to 60 mph. Sierra ridge gusts over 100 mph.

Primary concern for the next 48 hours – 

On-going Atmospheric River continues to bring heavy snow to the forecast area and will bring a complex mix of dangerous avalanche problems for the Advisory Forecast period. Overall - Very dangerous avalanche conditions exist. Travel in avalanche terrain not recommended, Natural avalanches likely; human- triggered avalanches very likely. Large avalanches in many areas; or very large avalanches in specific areas.

Tuesday thru Wednesday

Storm Slab - Very dangerous avalanche conditions exist throughout the region. Travel in avalanche terrain not recommended. Natural avalanches likely; human-triggered avalanches very likely due to wide spread Storm Snow instability on all aspects and elevations as another the storm enters the region, which is forecasted to deposit 2’ to 5’ plus of snow by Thursday. The new snow will fall on a recently saturated and fragile snowpack at the Low to Mid elevations. In the upper elevations a combination of rapid loading by heavy mountain snows has added significant weight to the snowpack and bonds to underlying adjacent layers are still forming, this combined with the potential for density changes within the new snow has increased the potential for Storm Slab avalanches.

Wind Slab – the approaching system is coming in with strong SW winds (40 to 60 mph, increasing to 50 to 65 mph Tuesday afternoon) combined with copious snow for transport will help form widespread fresh Wind Slabs NW-N-E-SE aspects in and around exposed terrain at all elevations. These can likely be found along ridgetops and in and around exposed terrain features that promote drifting.  Because of the strong winds, Wind Slabs may extend well down slope, be potentially deep, and very wide, depending on the terrain feature. Failures could be quite large.

Persistent Deep Weaknesses have been found throughout the forecast region and an avalanche failure in the upper snowpack could potentially trigger a step down failure deep in the snowpack triggering a potentially large and destructive avalanche, this is especially a concern north and south of the Mammoth Basin. 

Avalanche Character 1: Storm Slab
Storm Slab avalanches release naturally during snow storms and can be triggered for a few days after a storm. They often release at or below the trigger point. They exist throughout the terrain. Avoid them by waiting for the storm snow to stabilize.

Very dangerous avalanche conditions exist throughout the region. Travel in avalanche terrain not recommended. Natural avalanches likely; human-triggered avalanches very likely due to wide spread Storm Snow instability on all aspects and elevations as another the storm enters the region, which is forecasted to deposit 2’ to 5’ plus of snow by Thursday. The new snow will fall on a recently saturated and fragile snowpack at the Low to Mid elevations. In the upper elevations a combination of rapid loading by heavy mountain snows has added significant weight to the snowpack while bonds to underlying adjacent layers are still forming, this combined with the potential for density changes within the new snow has increased the potential for Storm Slab avalanches.

Avalanche Character 2: Wind Slab
Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

Very dangerous avalanche conditions exist throughout the region. Travel in avalanche terrain not recommended. Natural avalanches likely; human-triggered avalanches very likely. The approaching system is coming in with strong SW winds (40 to 60 mph, increasing to 50 to 65 mph Tuesday afternoon) combined with copious snow for transport will help form widespread fresh Wind Slabs NW-N-E-SE aspects in and around exposed terrain at all elevations. These can likely be found along ridgetops and in and around exposed terrain features that promote drifting.  Because of the strong winds, Wind Slabs may extend well down slope, be potentially deep, and very wide, depending on the terrain feature. Failures could be quite large. 

Avalanche Character 3: Persistent Slab
Persistent Slab avalanches can be triggered days to weeks after the last storm. They often propagate across and beyond terrain features that would otherwise confine Wind and Storm Slab avalanches. In some cases they can be triggered remotely, from low-angle terrain or adjacent slopes. Give yourself a wide safety buffer to address the uncertainty.

Early season storms In October and early December formed a combination of Melt/Freeze crusts and facets in the mid to upper elevations, primarily found on NW thru N thru East aspects forming a Persistent Deep Weaknesses that has been found throughout the forecast region. The recent heavy snows have added significant stress to the snowpack. An avalanche failure in the upper snowpack could potentially trigger a step down failure deep in the snowpack triggering a potentially large and destructive avalanche, this is especially a concern north and south of the Mammoth Basin. A recent avalanche observed in the Tele Bowls clearly illustrates this problem. Very dangerous avalanche conditions exist throughout the region. Travel in avalanche terrain not recommended. Natural avalanches likely; human-triggered avalanches very likely. 

 

Snowpack Discussion

The latest in a series of storms embedded in strong Atmospheric River will move into the region Tuesday with heavy snow through Thursday AM. Temperatures have begun to cool from the warm-up over the weekend, which brought heavy rain to the lower elevations and heavy snow to the highest elevations, a mixture of heavy precipitation in the mid-elevations.  Rain at the lower elevations has saturated the lower elevations snowpack with new snow now insolating it from the cooler temperatures moving into the region and hindering the deep snowpack from freezing and setting up, which increases the chances for Storm Slab failures due to weak substructure and weak bonding at the old/new snow interface, increasing the likelihood of avalanches triggering deeper weaknesses in the lower snowpack or eroding deep into the lower snowpack. In the mid to higher elevations, ongoing heavy snowfall has created Storm Slab conditions throughout the region and will continue into the next Forecast Period. Temperatures have begun to moderate from the 30’s to low 40’s over the weekend with temperatures in the 20 and low 30’s forecasted. Temperatures may briefly spike during the day Tusday with the potential for creating a denser layer of snow and an inverted snowpack

Forecasted strong SW winds (40 to 60 mph, increasing to 50 to 65 mph Tuesday afternoon, continuing into Wednesday) combined with copious snow for transport will help form widespread fresh Wind Slabs NW-N-E-SE aspects in and around exposed terrain at all elevations. These can likely be found along ridgetops and in and around exposed terrain features that promote drifting.  Because of the strong winds, Wind Slabs may extend well down slope, be potentially deep, and very wide, depending on the terrain feature. Failures could be quite large.

Early season storms In October and early December formed a combination of Melt/Freeze crusts and facets in the mid to upper elevations, primarily found on NW thru N thru East aspects forming a Persistent Deep Weaknesses that has been found throughout the forecast region. The recent heavy snows have added significant stress to the snowpack. An avalanche failure in the upper snowpack could potentially trigger a step down failure deep in the snowpack resulting in a potentially large and destructive avalanche, this is especially a concern north and south of the Mammoth Basin. A recent avalanche observed in the Tele Bowls clearly illustrates this problem.

 

recent observations

Mammoth Rock, Mammoth Basin (1/9/17) - Skinned up from the end of Old Mammoth Road to above Mammoth Rock around 9250 ft and back down the same way. Passed two seperate debris fields.  Debris piled up around a foot above snow against the uphill side of trees, some blocks up to 1 ft by 1 ft visible under new snow.  Both were under steep cliff bands west of the Rock.  One started around 9,000ft the other around 9,400ft, both crowns were obscured by new snow.  There were settlement cracks around many trees throughout the approach.  Cracking around skis was common, no shooting cracks.  Isolated collapsing when I moved into a wind loaded area. Two hand shear tests, both failed easily 25 and 30 cm down.  Seemed to be a thin layer of larger crystals where the failure occured.  In both locations I found 10 cm of fist hard new snow on the surface, 5 cm 1F wet snow under that, and 35 cm fist hard snow below that.

Avalanche Observation, Tele Bowls, Mammoth Basin (1/9/17) –

Slope: 35degrees, Trigger type: Natural

Aspect: North, Weak Layer: Other - explain below

Avalanche Width: 500ft., Terrain: Below Treeline

Elevation: 8,700ft., Bed Surface: Other - explain below

Avalanche Length: 1,000ft., Number of similar avalanches: 2

More detailed information about the avalanche: R4-D3.5 (large relative to path, could damage a railway car, destroy a car, a wood frame house).  Looks to have gone naturally during heavy rain event last night/yesterday.  Wet slab.  2.5ft+ crown, wrapping around upper parts of both entire bowls.  Northerly facing bowls, starting zones in the low 30s for the most part.  Failed and ran on top of upper October rain crust (~15cm above ground).  Underneath this rain crust was mix of frozen basal ice and 2-2.5mm facets.  Entire snowpack to ground, save for top few inches of new dry snow, was quite moist.  12'+ debris piles in bottom portion of bowls.  Some small trees were taken out, along with some 10" diameter dead ones.  Of note, avalanches ran in forested areas adjacent to open bowls in the lower 1/2.  

*Skiing and riding has now gone to crap in the bowls, between firm shallow bedsurface with icy spots to frozen chunder avy debris (hard to walk thru, let alone navigate a ski or board).

Punta Bardini/Old Growth, Mammoth Basin (1/9/17) - Route:  Propane tanks up Old growth to summit, back down, thru Tele bowls. Both Tele Bowls ripped out huge during heavy rain/storm event yesterday or last night. Snow pack was wet underneath top few inches of new snow from this morning to the ground below ~8900'.  Above this, snow pack was moist to ground up past at least 9,300'.  5cm thick rain crust at surface from last night/yesterday at the summit ~10,100', where new snow has blown off and not stuck. Pit dug to ground at 9,300', northerly aspect.  See attached profile.  Of note, snow was moist to the ground, and almost entirely isothermal (0 deg throughout except for a portion in middle with was -0.5- -1.0deg C, and very surface).  Stability tests (CT and ECT) did not show any concerning results (rough fractures with moderate to hard force, no propagation in ECTs).  No woomphing, cracking, or other signs of instability (remember, Punta Bardini is mostly fairly sheltered and relatively low elevation). Skiing/riding conditions very good above 8,900'! (3-5" nice fresh powder on top of supportive moist snow).  Below 8,900', rain crust seemed to be more distinct and breakable, requiring a little more light-footed-ness.  Below 8,500', even less new soft surface snow, and more punchy rain crust.

Mammoth Mountain Ski Patrol, Mammoth Basin (1/8/17) - Widespread avalanches triggered by explosives and ski cuts throughout mountain at all elevations.  12" crowns around Lincoln Mtn (10,000'), propagating across entire ridglines.  Up to 36" crowns on main lodge side  - upper cliffs (9,600'), lower cliffs.  Debris from gun shots on upper mountain from Scotty’s and Paranoids running far down the mountain with debris piles 6ft deep in bristlecone and running within 10ft of the patrol avalanche closure near Terry's run.  Monday Morning (1/9):  1-1.5" think rain crust on surface in the Bear, with several inches of dense snow on top at 9am.  Thick dense snow underlying rain crust. Slopes at 9,800' 7-8" new dense snow on top of 2-3" moist slush layer.  Lincoln Mtn: 1-2' crowns top of Avy 1 & 2 (new blown in snow sliding on top of bullet proof ice crust from yesterday / last night's rain layer freezing).  Several patrollers hitting ice layer, loosing edges and going for scary slides.  

Sierra Front, Tom’s Place to June Lakes (1/8/17) - Avalanche Type: Wet Slab, Loose Wet/Point-Release, Storm Slab

Slope: 35degrees, Trigger type: Natural

Aspect: Northeast, Weak Layer: Storm Snow

Terrain: Below Treeline, Elevation: 9 000ft.

Bed Surface: Unknown

More detailed information about visible avalanches: 

Quick road tour this afternoon while there was a break in the weather. Noted wide spread natural activity from Convict Lake to June Lakes.

- Rock Creek to McGee - still not cleared.

- Convict Lake - Avalanche activity visible from the lake on both sides of the valley (Mt. Laurel, Mt. Morrison), unknown start, ran short of the lake elevation.

- Solitude - debris visible in Banana Chute, start unknown.

- Punta Bardini - start unknown, debris to the young growth in the runout. D2-

- Mammoth Bowl - debris visible in the upper bowl, crown partially obscured, visible 1-2' x 200'. D2

- Dempsey's Don't - debris visible in the top end, unknown runout. D2

- Mammoth Rock - Loose/Wet x 2 ~ 8,700 and below, possibly running to ground. Numerous small Loose/Wet running short distances. D1 

- Carson Pk. and visible terrain north - extensive debris visible in Devils' Slide. Debris from central face in runout D2. Two debris fields D2 running just  south of Silver Lake.

- Sierra Front - numerous Loose/Wet starting at ~ 8,700' +/- from Mammoth Rock south to McGee Creek. D1 - D1+. Most active areas where there was little snow prior and recently loaded by the latest series of storms. As you move east of the crest rain up to 8,000', wet snow up to 9,000', heavy dense snow fall above, 10,000'. One to three feet new snow along 395 from Mammoth to June Lake.  

weather
  • Blizzard warning in effect until 10 am PST Wednesday...dangerous blizzard conditions due to heavy snow and strong winds will continue today through Wednesday morning. Periods of moderate to heavy snow will continue through Wednesday night.
  • Winter storm warning in effect from 10 am Wednesday to 4 am PST Thursday. Snow accumulations through Thursday morning: 1 to 3 feet for communities along highway 395. Totals of 3 to 6 feet above 7500 feet west of highway 395 with locally higher amounts. Snow levels: all valley     floors...may briefly rise to 7000 feet this afternoon and evening before falling again.
  • Winds: southwest 20 to 30 mph with gusts to 60 mph. Sierra ridge gusts over 100 mph.

A powerful Pacific storm will continue to affect the forecast region through at least Wednesday. Blizzard conditions are expected in the Eastern Sierra with snow continuing above 5000 feet.

Bottom line: do not travel in the Eastern Sierra. Life threatening blizzard conditions are occurring in places and will continue through Wednesday morning.

The next 24 hours will be very active to say the least...

Tuesday thru Wednesday - A second storm and AR is wreaking havoc in the Sierra at this time. Highway 395 is shut down in portions of Mono County due to blizzard conditions with visibility 10 feet per Mono County Sheriff`s Office. Wind gusts of 50 to 60 mph will create whiteout conditions along with heavy snow with multiple feet expected. Sierra ridge gusts will reach or exceed 150 mph tonight. Significant blowing and drifting snow will occur. Total snow accumulations up to 10 feet in the higher elevations and several feet in the lower elevations through Thursday morning. Drifts up to 20 feet are possible. Snow levels may briefly rise to 6500 feet. Winds will also create blowing and drifting snow with localized whiteout conditions. For Wednesday, the worst of the current winter storm should be over, but it will not be a clean break for the Sierra as areas of light to moderate snow will likely continue through much of the day, bringing a few more inches of snowfall. Brisk southwest to west winds will continue and although wind speeds won`t be as strong compared to today, most areas should still see gusts at least 40 mph, with Sierra ridge gusts over 80 mph.

Thursday thru Friday - This precip break for most lower elevations will be short lived as an upper low following on the heels of the previous storm is on track to move inland across north central CA and spread more precip into the Sierra by Thursday. Most recent guidance favors a central Sierra and western NV track with a surface low forming between Tonopah and Beatty NV (a weak "Tonopah Low" pattern).  The result of these recent trends is an increasing chance for another 5-10 inches of snow are possible for the Sierra. By Thursday night, the steady snow will taper to isolated-scattered snow showers. Friday through early next week, the medium range guidance has remained consistent with building a ridge over CA-NV. A few leftover snow showers may linger in southern Mineral-Mono early Friday morning as Thursday`s low departs, before the ridge axis amplifies and pushes the storm track farther north. Inversion conditions will keep daytime temps below average. 

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
  Tuesday Tuesday Night Wednesday
Weather: CLOUDY. SNOW AND BLOWING SNOW. CLOUDY. HEAVY SNOW AND BLOWING SNOW. CLOUDY. SNOW IN THE MORNING, THEN CHANCE OF SNOW IN THE AFTERNOON.
Temperatures: 27 TO 33 deg. F. deg. F. 19 TO 24 deg. F. deg. F. 25 TO 31 deg. F. deg. F.
Wind direction: SOUTHWEST SOUTHWEST SOUTHWEST
Wind speed: 25 TO 40 MPH. GUSTS UP TO 70 MPH. 25 TO 40 MPH. GUSTS UP TO 70 MPH. 20 TO 30 MPH WITH GUSTS TO 60 MPH.
Expected snowfall: 8 TO 16 in. 18 TO 30 in. 8 TO 12 in.
Over 10,000 ft.
  Tuesday Tuesday Night Wednesday
Weather: CLOUDY. SNOW AND BLOWING SNOW. CLOUDY. HEAVY SNOW AND BLOWING SNOW. CLOUDY. SNOW IN THE MORNING, THEN CHANCE OF SNOW IN THE AFTERNOON.
Temperatures: 22 TO 28 deg. F. deg. F. 11 TO 17 deg. F. deg. F. 18 TO 24 deg. F. deg. F.
Wind direction: WEST SOUTHWEST SOUTHWEST
Wind speed: 40 TO 60 MPH WITH GUSTS TO 120 MPH SHIFTING TO THE SOUTHWEST 50 TO 65 MPH WITH GUSTS TO 135 MPH IN THE AFTERNOON. 45 TO 65 MPH WITH GUSTS TO 125 MPH INCREASING TO 55 TO 75 MPH WITH GUSTS TO 160 MPH AFTER MIDNIGHT. 35 TO 55 MPH WITH GUSTS TO 85 MPH.
Expected snowfall: 8 TO 16 in. 18 TO 36 in. 8 TO 14 in.
Disclaimer

This Snowpack Summary 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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