Avalanche Advisory: Tuesday - Apr 10, 2018

 
 
 
 
 
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THIS AVALANCHE ADVISORY EXPIRED ON April 12, 2018 @ 6:24 am
Avalanche Advisory published on April 10, 2018 @ 6:24 am
Issued by Clancy Nelson - Eastern Sierra Avalanche Center

Tuesday: Triggering loose wet avalanches will become increasingly possible as the spring snow becomes wet and unsupportable on steep slopes by mid-day. Watch for rollerballs and small wet sluffs or boot-top penetration into wet snow as signs that you should move to shady, lower-angle slopes. Loose wet avalanches often originate from rocky areas and vegetation where the snow receives and retains more heat.

Wednesday: The threat of avalanches will most likely decrease on Wednesday as fast-moving storm systems bring a cooling trend and even stronger winds. Use standard caution in your backcountry travels and look for unstable snow on isolated terrain features. Loose wet avalanches will not be impossible. Look for wet snow and rollerballs in steep terrain and near rocky areas. Small wind slabs may form by late afternoon, especially North of Mammoth if snow begins to fall during daylight hours. Blowing snow just under steep ridgelines, in the tops of chutes, and on the sidewalls of gullies will be the biggest clues of increasing instability. Wind slabs will likely form overnight into Thursday.

For the entire forecast period: Early in the day slide-for-life conditions exist on steep slopes where the firm snow surface could make a simple slip and fall very dangerous. Crampons and an ice ax could reduce your vulnerability to icy snow conditions on steep slopes.

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Near Treeline

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Below Treeline
Avalanche Problem 1: Loose Wet
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Loose wet instabilities such as rollerballs and point releases will be increasingly possible by late morning on Tuesday. Clouds overnight Monday and above freezing temperatures across the area will make it easy for the snow to become wet and lose cohesion on Tuesday at all aspects and elevations that have enough snow coverage. Unsupportable wet snow, where you can sink in to your boot tops means it’s time to move to less steep and colder slopes. Cooler temperatures, strong winds, and daytime clouds will most likely improve the problem somewhat by Wednesday.

Avalanche Problem 2: Wind Slab
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Strong wind will be the primary weather factor of note for the next two days. A moisture-starved system will pass through Tuesday night with little in the way of precipitation. By late Wednesday afternoon, especially North of Mammoth, small wind slabs could form as a second system moves in with slightly higher chances of snow. Only the most favored features: like the leeward sides of steep ridgelines and the tops of alpine gullies are likely to see wind slab formation during daylight hours Wednesday afternoon. Daytime wind slab activity is expected to be small. Wind slabs will likely form overnight Wednesday.

advisory discussion

The recent storm 4/6-4/7 brought on a big avalanche cycle as rain pounded the snow and loose wet and wet slab avalanches ran bigger and on lower angled slopes than usual. Snow fell at the very highest elevations, especially around the Bishop area. The moisture seems generally to have passed through the snowpack at the middle and upper elevations where runnels are a sign that the snowpack has consolidated. A drop in temperatures Saturday and Sunday nights allowed for a solid re-freeze. However, spring-like conditions returned Sunday with very warm temperatures, sunny skies, and little in the way of wind. Last night (Monday) almost nowhere in the forecast area reported temperatures below 32 deg F. That, coupled with the hazy clouds overnight, prevented the snowpack from setting up again and will slightly increase the risk of wet snow instability on Tuesday.

High winds will dominate this forecast period as fast-moving spring storms pass through the region. Little is expected in the way of snowfall but forecasts are showing the possibility of accumulation North of the Mammoth area by Wednesday afternoon. Even a few inches of snow accompanied by moderate to strong winds can form sensitive slabs that could be triggered near features that promote drifting. Though wind slab formation is expected to be quite limited through the day Wednesday, larger drifts are expected to form overnight going into Thursday. Areas that receive the most snow will be of greater risk.

recent observations

4/9- Spring Conditions in Valentine Cirque

Temperatures @ 0400

Loc                                          Highs/Lows

Virginia Ridge, 9409’:             55/39 deg F., No Freeze
Tioga Pass, 9972’:                 55/33 deg F., No Freeze
Agnew Pass, 9355’:              66/35 deg F., No Freeze
June Mt., 9148’:                    60/43 deg F., No Freeze
Mammoth Pass, 9500’:          64/35 deg F., No Freeze
Sesame Plot, 9014’:              60/42 deg F., No Freeze
Ch. 22-MMSA, 10,067’:         58/39 deg F., No Freeze
Summit-MMSA, 11,053’:       47/34 deg F., No Freeze
Rock Creek, 9600’:                56/32 deg F., 1 hr below freezing
South Lake, 9580’:                64/37 deg F., No Freeze
Sawmill, 10,200’:                   55/34 deg F., No Freeze

Weather and CURRENT CONDITIONS
weather summary

...WIND ADVISORY IN EFFECT FROM 2 PM TUESDAY AFTERNOON TO 11 PM PDT WEDNESDAY…

 A couple of fast-moving systems will produce gusty winds and light amounts of rain and snow are possible at times today through Thursday.

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: Mostly cloudy. Mostly cloudy then becoming partly cloudy. Scattered showers in the evening. Partly cloudy then becoming mostly cloudy. Chance of snow showers in the afternoon.
Temperatures: 49 to 59 deg. F. 30 to 35 deg. F. 42 to 52 deg. F.
Wind Direction: S-SW SW SW
Wind Speed: 10 to 15 mph with gusts to 35 mph increasing to 20 to 30 mph with gusts to 55 mph in the afternoon. 20 to 35 mph. Gusts up to 60 mph decreasing to 45 mph after midnight. 15 to 20 mph with gusts to 45 mph increasing to 20 to 30 mph with gusts to 55 mph in the afternoon.
Expected snowfall: 0 in. 40% probability...up to 1 inch. 60% probability...0 in. 40% probability...up to 1 inch. 60% probability...0 in.
Over 10,000 ft.
Tuesday Tuesday Night Wednesday
Weather: Mostly cloudy. Mostly cloudy then becoming partly cloudy. Scattered snow showers in the evening. Partly cloudy then becoming mostly cloudy. Chance of snow showers in the afternoon.
Temperatures: 43 to 49 deg. F. 25 to 31 deg. F. 37 to 43 deg. F.
Wind Direction: SW SW SW
Wind Speed: 30 to 45 mph with gusts to 70 mph increasing to 35 to 55 mph with gusts to 80 mph in the afternoon. 40 to 60 mph with gusts to 85 mph decreasing to 30 to 45 mph with gusts to 65 mph after midnight. 30 to 45 mph. Gusts up to 60 mph increasing to 70 mph in the afternoon.
Expected snowfall: 0 in. 40% probability...up to 1 inch. 60% probability...0 in. 40% probability...up to 1 inch. 60% probability...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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