Avalanche Advisory: Monday - Mar 26, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON March 27, 2018 @ 7:00 am
Avalanche Advisory published on March 26, 2018 @ 7:00 am
Issued by Doug Lewis - Eastern Sierra Avalanche Center

Monday (3/26) – The overall avalanche hazard is MODERATE. Natural avalanches are unlikely, human triggered Wind Slab avalanches are possible near and above treeline. Evaluate wind deposited snow carefully on exposed leeward slopes, below ridgelines, and crossloaded gullies. Loose Wet avalanches will be a concern on solar aspects (W-SW-S-SE) especially in steep rocky terrain that has recently become snow-covered near treeline and below (~10500' and below) where strongest heating will take place. Natural avalanches are unlikely, triggered releases possible from treeline and below. 

2. Moderate

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

2. Moderate

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

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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A quick system passed through the region 3/24 overnight with 1 to 4” mainly from Rock Creek north with SW winds forming large wind slabs on NW-N-NE-E-SE aspects. Previously formed Wind Slabs from over the past few days have had time to strengthen and are expected to be stubborn to trigger, though not impossible. Winds are forecasted to veer to the North – Northeast, today, with 1 to 4” of new low-density snow available for transport, anticipate Wind Slabs forming above treeline  (~10,000’) on NW-W-SW-S-SE aspects. The newer wind slabs are expected to be smaller but more reactive. Evaluate the snowpack and terrain carefully. Dense snow deposits 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, triggered releases are possible.

 

Avalanche Problem 2: Loose Wet
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The weather forecast calls for high temperatures to climb into the mid 30’s (likely warmer)below 10,000’ with light northerly winds and sunny skies. The combination will allow the surface snow to begin warming and possibly become wet and saturated, especially in steep rocky terrain up to ~10,000’, possible 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. Anticipate lower elevations warm more quickly than mid-elevations. Extra caution is advised in and around rock outcrops, below cliff bands, or 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. Small point releases are indicators that the surface snow is becoming wet; as the snow becomes saturated larger avalanches are increasingly possible. Loose Wet can trigger larger deeper releases. Timing is critical for avoiding Loose Wet releases. Time your travels to be out of steep sunny terrain before the snow becomes saturated from the heat of the day. For near tree line and below, natural avalanches are unlikely, triggered releases are possible, especially below 10,000’ in sheltered or rocky terrain. The trend for the next couple of days will see temperatures rise appreciably, increasing 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.

 

advisory discussion

The recent spat of storms brought 4 to 6’ of snow and has helped turn the corner on a rather lean season. The rapid series of storms produced 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 into the snowpack reducing the concern for triggered release, except possibly in very isolated areas 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.

The recent storms were accompanied by strong SW winds, pre & post frontal passage, forming widespread 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. As winds veer to the North-Northeast today (3/26), moderate winds above ~10000’ will begin to forming new and tender Wind Slabs on NW-W-SW-S-SE aspects, near and above treeline (~10000’ and above).

Loose Wet – temperatures are forecasted to climb into the mid 30’s today and begin appreciably warm the snow for the first time since the recent series of storms passed through the region. Anticipate a developing cycle of Loose Wet, with a few possible today and becoming increasingly likely tomorrow (3/27) with high temperatures forecasted to climb into the mid 40’s. Today, Loose Wet release will generally be small on solar aspects (W-SW-S-SE), primarily tree line and below, as temperatures begin to rebound to seasonable.

Loose Dry sluffs may be encountered in isolated steep terrain, near and below tree line in sheltered locations. While these slides are not a concern for burial, they can sweep a rider into potential hazardous terrain or obstacles.

 

 

 

 

 

 

Weather and CURRENT CONDITIONS
weather summary

Monday thru Tuesday – A ridge of high pressure centered over the eastern Pacific slowly builds over eastern California through midweek. A significant warming trend beginning Tuesday with above average temperatures by Wednesday. Winds will increase along the Sierra crest tonight into Tuesday morning as the ridge begins to press inland and a surface high settles into Nevada. This will bring enhanced easterly winds over exposed Sierra ridges, especially along the immediate crest     where winds are expected to gust 60-80 mph.

Thursday thru Sunday - Above average temperatures are expected Thursday and Friday as the high-pressure center shifts to the Southwest US and starts to    flatten. The medium range guidance scenarios diverge over the Easter weekend but thicker clouds and light showers with possible additional cooling. It appears temperatures will drop a few degrees over the weekend, possibly back to near     seasonal averages in the Sierra by Sunday. 

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: Sunny Clear Sunny
Temperatures: 27 to 33 deg. F. 15 to 20 deg. F. 39 to 45 deg. F.
Wind Direction: North North North
Wind Speed: 10 to 15 mph with gusts to 30 mph. 10 to 20 mph. Gusts up to 40 mph. 10 to 15 mph with gusts to 40 mph.
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Monday Monday Night Tuesday
Weather: Sunny Clear Sunny
Temperatures: 20 to 25 deg. F. 12 to 17 deg. F. 33 to 38 deg. F.
Wind Direction: Northeast North Northeast
Wind Speed: 20 to 35 mph with gusts to 45 mph. 25 to 40 mph with gusts to 60 mph increasing to 30 to 45 mph with gusts to 70 mph after midnight. 20 to 35 mph with gusts to 55 mph.
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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