Avalanche Advisory: Tuesday - Mar 27, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON March 28, 2018 @ 6:52 am
Avalanche Advisory published on March 27, 2018 @ 6:52 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center

Tuesday (3/27) – The overall avalanche hazard is CONSIDERABLE. Near treeline and below, Loose Wet natural avalanches are possible, human triggered avalanches are likely on solar aspects (W-SW-S-SE). Use extra caution in sheltered or steep rocky snow-covered terrain where strongest heating will take place. Forecasted strong Northerly winds will form Wind Slabs near and above treeline (~9000 – 10500’) on W-S-E aspects, especially from Mammoth to June where there is more loose transportable snow. Natural avalanches are unlikely (but not impossible), triggered releases possible.  

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Loose Wet
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The weather forecast for today (Tuesday) calls for a dramatic warm-up with high temperatures climbing into the upper 30’s and mid 40’s below 10,000’ with light to moderate northerly winds and sunny skies. The combination will allow the surface snow to warm and possibly become wet and saturated, especially in steep rocky terrain as high as ~10,000’, possibly a bit higher. Loose Wet avalanches are increasingly possible on SE-S-SW-W aspects where there is appreciable warming of the surface snow, especially recently snow covered steep rocky faces (i.e. Laurel Mountain - South Face). Generally, the snow at the lower elevations thaws more quickly. Use extra caution in and around rock outcroppings, cliff bands, or sheltered areas where the snowpack may heat up more quickly and triggered releases are more likely. Signs of unstable snow: large roller balls, deep ski penetration, and small point releases. Loose Wet can trigger larger deeper releases. Time your travels to be out of steep sunny terrain before the snow becomes saturated from the heat of the day. From near tree line (below ~10,000’) and below, natural avalanches are possible, triggered releases are likely, especially in sheltered or rocky terrain. The trend for the next couple of days will see temperatures rise appreciably, maintaining the potential for Loose Wet releases.  

Loose Wet slides are dense / heavy and are capable of carrying a rider into hazardous terrain or lead to possible burial when combined with a terrain trap.

 

Avalanche Problem 2: Wind Slab
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A recent series of storms with strong SW winds formed extensive wind slabs on NW-N-NE-E-SE aspects. The lingering Wind Slabs have had time to strengthen and are expected to be stubborn to trigger, though not impossible. Strong Northerly winds in the Alpine are forecasted for the region today, anticipate Wind Slabs forming near and above treeline  (~10,000’ and above) on W-S-E aspects. These should be generally shallow and small in nature. Evaluate the snowpack and terrain carefully. Dense snowdrifts are a telltale sign and will likely be encountered: immediately below ridgelines or corniced slopes, in crossloaded gullies, or near terrain features that encourage drifting. Hand shear assessments and pole probing can help identify poorly bonded or suspended slabs. Natural avalanches are unlikely but not impossible, triggered releases are possible.

advisory discussion

Loose Wet – temperatures peaked in the low 30’s yesterday at a few sites but generally remained a bit cooler than anticipated, which kept the snow temperatures a bit colder than predicted and suppressed potential Loose Wet activity. Today’s temperatures are forecasted to climb into the upper 30’s to mid 40’s today below 10000’.  If the forecast holds true, this will be the first real significant warming since the recent series of storms passed through the region. Strong winds in the Alpine will help cool the surface snow from treeline and above, generally limiting the potential for Loose Wet to treeline (~9000’ to ~10,500’) and below. Today, a few small natural avalanches are possible on solar aspects (W-SW-S-SE) and becoming increasingly likely tomorrow (3/28) as temperatures climb into the mid to upper 40’s.

The recent series of storms were accompanied by strong SW winds forming widespread lingering Wind Slabs on NW-N-NE-E-SE aspects. These Wind Slabs have generally had enough time to strengthen and bond to the underlying snow and as a result, less reactive but a potential lingering concern in steep complex terrain. Strong Northerly winds are forecasted through Wednesday AM above 10,000’, with moderate winds below. Above ~10000’ on open exposed terrain, I anticipate small shallow Wind Slabs forming in favored locations (leeward slopes, under cornices, near rock outcrops, etc.), especially areas with large windward fetches. Tender Wind Slabs are possible on W-S-E aspects, near and above treeline (~10000’ and above).  I don’t expect this to be a widespread problem. More of a concern in favored localized areas.

The recent spat of storms brought 4 to 6’ of snow and has helped turn the corner on a rather lean season. The series of storms began to roll into the region in early March and continued through 3/22 with the last storm producing the biggest avalanche cycle of the season with impressive debris fields in many of the runouts throughout the range. The heavy snow accumulations have buried the persistent weak layers deep in the snowpack reducing the potential for triggered release, except possibly in isolated areas near Bishop or north of June where it could be closer to the surface. Prior to the recent series of storms, the facet layers were showing signs of sintering and rounding, with some shallow areas becoming wet and refreezing, becoming stronger in the process with stability tests trending stronger. 

Weather and CURRENT CONDITIONS
weather summary

Tues thru Thursday - High pressure settling into northeast California has brought moderate northeast winds to Mono County crests, with gusts between 55-80 mph. Stronger winds should persist into this morning before easing down. The rest of the week will feature dry and warm days with chilly mornings. Afternoon highs will climb into the 40s to 50s.
 
Friday thru Next Week - Friday currently looks to be the warmest day for the upcoming week as low amplitude ridge axis moves toward the Sierra. For Easter weekend, a weak shortwave looks to approach the CA coast, flattening the ridge and bringing thicker cloud cover across the region with a slim possibility of a few very light showers Saturday-Saturday night. In addition, a longwave trough moving across the Rockies may drive a weak back door cold front across the Great Basin. The cloud cover Saturday night will limit overnight cooling, with early morning temperatures for Easter looking to range from upper 20s-lower 30s for Sierra    valleys. 

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: Sunny Clear Sunny
Temperatures: 39 to 45 deg. F. 23 to 28 deg. F. 46 to 52 deg. F.
Mid Slope Winds: North North North
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Sunny Clear Sunny
Temperatures: 33 to 38 deg. F. 22 to 27 deg. F. 38 to 43. deg. F.
Ridge Top Winds: North Northeast North
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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