Avalanche Advisory: Monday - Apr 2, 2018 | Eastern Sierra Avalanche Center

THIS AVALANCHE ADVISORY EXPIRED ON April 3, 2018 @ 6:59 am
Avalanche Advisory published on April 2, 2018 @ 6:59 am

Issued by Doug Lewis - Eastern Sierra Avalanche Center

Bottom Line

Monday (4/2) – As the snow begins to thaw during the day, the avalanche danger will quickly rise to MODERATE from near treeline and below, where there’s snow. Loose Wet avalanches are especially possible in steep, rocky, or vegetated terrain. Watch for extensive rollerballs and small point releases or deep wet snow at the surface.

* Slide For Life - Firm spring conditions, especially in the upper elevations, can make it incredibly hard to arrest a fall on steep slopes. If planning on riding in steep or complex terrain the ability to arrest a fall is critical. Crampons, ice axes, and a helmet are strongly advised.

1. Low

Above Treeline

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

2. Moderate

Near Treeline

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

2. Moderate

Below Treeline

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

Avalanche Problem 1: Loose Wet

Type ?
Aspect/Elevation ?
Likelihood ?

Certain

Very Likely

Likely

Possible

Unlikely
Size ?

Historic

Very Large

Large

Small

Overnight lows continue to struggle to fall below freezing at many locations, permitting only a modest freeze. Today’s forecasted high temperatures will be a bit cooler with highs in the upper 40’s to low 50’s below 10,000’, upper 30’s to low 40’s above 10,000’. Cloud cover and moderate winds in the upper elevations today will play a key role in how quickly the snow surface thaws. The forecast is for mostly cloudy conditions to partly cloudy skies with moderate Westerly winds. The combination of clouds and wind will help slow the daily thaw, especially on solar aspects. Loose Wet avalanches are possible from near treeline (~10500’-9000') on E-SE-S-SW-W-NW aspects but especially on SE-S-W aspects where there is more solar warming of the surface snow. Below treeline, Loose Wet releases are possible all aspects due weak overnight freezes. Generally, the snow at the lower elevations thaws more quickly. Terrain can accentuate the problem, such as cirques and bowls, and rocky gullies can amplify and retain more heat than open slopes. 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, especially in the lower elevations (~9000’ and below) where the snow has become isothermal and saturated during the day. Time your travels to be out of steep terrain before the snow becomes overly saturated from the heat of the day. Natural avalanches are unlikely (small point releases possible), triggered releases are possible, especially in sheltered, steep, or rocky terrain.

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

Loose Wet – Spring conditions continue to be the dominate theme with temperatures overnight once again struggling to fall below 32 degrees for any length of time at most reporting stations. Todays forecast is calling for mostly cloudy to partly cloudy skies as a cold front passes to the north of the forecast area with moderate Westerly winds aloft. The combination of cooler temps, cloud cover, and moderate winds will likely slow daily thawing in the mid and upper elevations (~10,500’ and above) and limit Loose Wet activity to mostly solar aspects below ~10,500’ or lower. Below ~10,500’, limited convective cooling and mixing will see the surface snow thaw more rapidly as temperatures begin to climb during the day. Solar aspects will warm the quickest due to the direct sunlight, with northerly and shaded aspects following as the ambient air temperatures begin to climb during the day. Northerly and shaded slopes above ~9000’ are seeing strong warming at the surface but remain below freezing deeper in the snowpack. As a result, Loose Wet releases on northerly aspects are less likely to erode deeply into the snowpack and will generally be smaller in size.

Yesterday, moderate winds aloft helped to keep temperatures in the upper elevations cooler limited thawing to just the surface snow (aka good corn skiing). High temperatures today will be cooler and additional cloud cover will limit Loose Wet activity to treeline and below (~10500 and below), with the biggest concern focused on solar aspects.

If the snow is so deep that it makes it difficult to turn or boot penetration becomes excessive, this is a strong sign that the surface snow is saturated and loose it’s time to move onto slopes with firmer snow, shady slopes, or lower angles.

recent observations

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Dunderberg, SE Face (4/1)

Mammoth Rock Bowl, Sherwin Trees: Warming (3/31)

Old Man's Bowl: Tracking Warming (3/31)

Lower Esha (3/29)

Red Cone: Thaw (3/29)

Temperatures @ 0400

Loc Highs/Lows

Virginia Ridge, 9409’: N/A
Tioga Pass, 9972’: 50/25 deg F. 7hrs freezing
Agnew Pass, 9355’: 62/28 deg F, 7hrs freezing
June Mt., 9148’: 56/38 deg F, no freeze
Mammoth Pass, 9500’: 58/29 deg F, 4hr freezing
Sesame Plot, 9014’: 52/38 deg F, no freeze
Ch. 22-MMSA, 10,067’: 47/33 deg F, no freeze
Summit-MMSA, 11,053’: 39/27 deg F, 9hrs freezing
Rock Creek, 9600’: 45/35 deg F, no freeze
South Lake, 9580’: 62/31 deg F, 4hrs freezing
Sawmill, 10,200’: 54/27 deg F, 4hrs freezing

Weather and CURRENT CONDITIONS

weather summary

Mon thru Wednesday - Cooler day today as colder air aloft moves through the Great Basin with gusty winds in the 25-30 mph range. Expect increasing clouds midweek as moisture begins to push into the Pacific Northwest with little to no accumulation is expected through midweek. Thursday will be the last quiet day of the week

Friday and Beyond - A warm and very moist storm system approaches the west coast and bring periods of heavy rain and wind to the region Friday through Saturday. Upper trough and moisture plume are to arrive a little sooner with more widespread precipitation Friday ahead of the main jet/frontal support that is still expected to arrive Friday night. Model soundings show snow levels rising to near 10000 feet with this initial moisture plume. Friday night into Saturday, expected QPF totals easily approaching 2.5 to 3" along the crest and 1-2" west of Highway 395. Significant rises on creeks and streams are likely by Saturday morning and depending on the ripeness of the snowpack. A notable front will work southward through the area Saturday with much of the heavier precipitation falling along and ahead of it. The GFS continues to indicate a rather abrupt end to the heavier rain as the cold front passes with snow levels dropping to Sierra valleys by late afternoon Saturday. The ECMWF is a little slower but also shows this trend of cooling aloft. While precipitation will be lighter on the backside, snow showers may bring several inches of snow to higher passes late Saturday into early Sunday morning. Strong gusty winds will develop over the ridges Thursday night and continue thru Saturday.

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:	Mostly cloudy then becoming partly cloudy.	Partly cloudy then becoming clear.	Sunny.
Temperatures:	45 to 53 deg. F.	23 to 28 deg. F.	46 to 54 deg. F.
Mid Slope Winds:	West	Northwest	Light winds
Expected snowfall:	0 in.	0 in.	0 in.

Over 10,000 ft.

	Monday	Monday Night	Tuesday
Weather:	Partly cloudy.	Partly cloudy then becoming clear.	Sunny.
Temperatures:	37 to 42 deg. F.	20 to 25 deg. F.	39 to 44 deg. F.
Ridge Top Winds:	West	West	Southwest
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.