THIS AVALANCHE ADVISORY EXPIRED ON January 30, 2018 @ 7:00 am
Avalanche Advisory published on January 29, 2018 @ 7:00 am
Issued by Andy Anderson - Tahoe National Forest

The avalanche danger remains MODERATE due to some wind slabs lingering in near and above treeline terrain and the potential for loose wet avalanches as the day warms up.  Some isolated persistent slabs may also linger in some near and below treeline areas, especially in the Carson Pass and Ebbetts Pass regions. 

2. Moderate

?

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

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.
    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

More warm weather today will cause loose wet instabilities including roller balls, pinwheels, and point release avalanches to become possible on steep sun-exposed slopes as the surface snow becomes wet. The forecasted afternoon cloud cover could dimish the chances of larger loose wet instabilities on slopes where the clouds provide shade. These clouds could also bounce some of the heat back onto other aspects and cause wet sticky snow to form on some more northerly aspects. Most of these loose wet instabilities should not entrain enough snow to bury a person, but they could knock a person over or push a person into terrain where collisions or a fall would have serious consequences. 

Avalanche Problem 2: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Some wind slabs may still linger on near and above treeline N-NE-E aspects and cross-loaded SE and NW aspects. Complex or extreme terrain like unsupported slopes, cliffy areas, or steep exposed couloirs hold the best potential for unstable wind slabs, but some could also exist in the most heavily wind-loaded terrain. Avalanches resulting from the failure of these wind slabs could involve enough snow to bury or injure a person (size D2). In addition to these wind slabs, large fragile cornices also exist above many wind-loaded slopes.

Use clues like wind drifted snow, cornices above slopes, wind pillows, and wind-sculpted snow surfaces to identify and avoid areas of potentially unstable wind slabs, and give cornices a wide berth since they often break well away from their edges.

Avalanche Problem 3: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

While they are unlikely in most of the forecast area since other persistent weak layers have become unreactive, isolated persistent slab avalanches may remain possible in the Carson Pass and Ebbetts Pass areas. If a persistent slab avalanche does occur, it could involve enough snow to bury or injure a person (size D2 with some potential for an isolated D3). A layer of loose weak snow near a crust 8 to 18 inches below the surface represents the persistent weak layer for this problem (near crust facets). Observations including snowpit tests and snowmobile triggered shooting cracks yesterday continue to indicate that this layer remains weak on some near and below treeline NW-N-NE facing slopes in the Carson Pass and Ebbetts Pass areas. Significant uncertainty still remains as to how widespread this problem may be.

Look for and avoid avalanche terrain in any areas where snow surface cracking, snowpack collapse with a possible whumpfing sound, and/or unstable snowpit test results are occurring.

recent observations

* Snowmobile cuts triggered shooting cracks on the buried persistent weak layer of near crust facets in the Ebbetts Pass area yesterday. 

* Snowpit tests targetting the near crust facet layer near Ebbetts Pass and some tests on Red Lake Peak (Carson Pass area) indicated that if the layer breaks fractures can still travel along that layer

* Most snowpit tests and observations in the Mt. Rose backcountry on Incline Lake Peak and Tamarack Peak and tests on Mt. Judah (Donner Pass area) indicated that the older weak layers have gained strength and that fracture propagation along the old layers has become unlikely. 

* Some skier triggered cracking occurred on wind-loaded test slopes on Mt. Judah (Donner Pass area). Large tender cornices also existed above most wind-loaded slopes.

* Minor E wind scouring had occurred in some areas on Red Lake Peak (Carson Pass area) and on Incline Lake Peak (Mt. Rose backcountry) but observers did not report any significant wind slabs on westerly aspects

* Observers reported small loose wet instabilities and wet sticky surface snow during the afternoon on Incline Lake Peak, Red Lake Peak, Mt. Judah, and in the Ebbetts Pass area.

Weather and CURRENT CONDITIONS
weather summary

Calm weather has allowed cold air and fog to sink into the valleys overnight. As a result temperatures at the lower elevations fell below freezing during the night. At the upper elevations, temperatures remained warm with sensors above 8000 ft. reporting overnight lows in the upper 30's to mid 40's. The high-pressure ridge over the region will allow the unseasonably warm weather to continue. Some increased cloud cover may start to develop this afternoon and the southwest winds should start to increase as a dry front approaches the area. 

Weather observations from along the Sierra Crest between 8200 ft. and 8800 ft.
0600 temperature: 34 to 46 deg. F.
Max. temperature in the last 24 hours: 48 to 53 deg. F.
Average wind direction during the last 24 hours: Variable between NE and SW
Average wind speed during the last 24 hours: 5 to 10 mph
Maximum wind gust in the last 24 hours: 34 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 30 to 56 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Partly sunny this morning becoming mostly cloudy by this afternoon Mostly cloudy with clouds starting to decrease after midnight Partly cloudy becoming mostly sunny
Temperatures: 48 to 54 deg. F. 30 to 35 deg. F. 49 to 55 deg. F.
Wind Direction: Variable Southwest Southwest
Wind Speed: Light with gusts to 25 mph in the afternoon Light increasing to 10 to 15 mph with gusts to 30 after midnight 15 to 20 mph with gusts to 40 mph
Expected snowfall: 0 in. 0 in. 0 in.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Partly sunny this morning becoming mostly cloudy by this afternoon Mostly cloudy with clouds starting to decrease after midnight Partly cloudy becoming mostly sunny
Temperatures: 46 to 51 deg. F. 30 to 35 deg. F. 44 to 50 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 15 to 25 mph with gusts to 35 mph in the afternoon 20 to 30 mph with gusts to 40 mph increasing to 55 mph after midnight 20 to 35 mph with gusts to 60 mph
Expected snowfall: 0 in. 0 in. 0 in.
Disclaimer

This avalanche advisory is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This advisory covers the Central Sierra Nevada Mountains between Yuba Pass on the north and Ebbetts Pass on the south. Click here for a map of the forecast area. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the Avalanche Advisory call (530) 587-3558 x258