Backcountry Avalanche Forecast Central Sierra Nevada
Sierra Avalanche Center
www.sierraavalanchecenter.org
- Issued
- Wednesday, December 6, 2023 - 6:49AM
- Expires
- Thursday, December 7, 2023 - 6:49AM
- Author
- Steve Reynaud
The Bottom Line
A storm will begin late this afternoon through Thursday bringing increased winds and snow to our area. This new snow will add additional weight to our variable and, in some cases, weak snowpack. Over the snow recreation continues to be limited for backcountry travelers due to low snow conditions. Avalanche danger is expected to quickly rise this evening and overnight.
Avalanche Danger
Wednesday, December 6, 2023
Thursday, December 7, 2023
- Above Treeline3 - Considerable
- Near Treeline3 - Considerable
- Below Treeline3 - Considerable
 1 - Low |  2 - Moderate |  3 - Considerable |  4 - High |  5 - Extreme | |
|---|---|---|---|---|---|
| Travel Advice | Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. | Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. | Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential. | Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. | Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain. |
| Likelihood of Avalanches | Natural and human-triggered avalanches unlikely. | Natural avalanches unlikely; human-triggered avalanches possible. | Natural avalanches possible; human-triggered avalanches likely. | Natural avalanches likely; human-triggered avalanches very likely. | Natural and human-triggered avalanches certain. |
| Avalanche Size and Distribution | Small avalanches in isolated areas or extreme terrain. | Small avalanches in specific areas; or large avalanches in isolated areas. | Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. | Large avalanches in many areas; or very large avalanches in specific areas. | Very large avalanches in many areas. |
Avalanche Problems (2)
Problem #1: Wind Slab
Problem Type
Aspect/Elevation
Likelihood
Size
SW winds will be in the strong to gale force range today. Snow available for wind transport remains limited, but small amounts of blowing snow will occur forming small winds slabs in near and above treeline terrain. As snow begins to fall late this afternoon and tonight, larger wind slabs will begin to form in these areas. In some terrain where wind slabs will be forming, previous weak faceted snow exists that could easily be overloaded by the newly forming wind slabs.
Look for blowing snow, new cornice development, and wind pillows as to where wind slabs will be forming.
Problem #2: Persistent Slab
Problem Type
Aspect/Elevation
Likelihood
Size
(12/4/2023)
Shallow and weak snowpack on N side of Hourglass Bowl. Tamarack Peak.
Photo: SAC
Weak faceted snow continues to exist on NW-N-NE aspects above 8500' with weak facet/rain crust combinations existing below 8500’. These weak layers are highly variable in distribution and strength with a high level of uncertainty. The forecasted storm starting late this afternoon through Thursday, will add considerable weight to our weak snowpack structure. This additional weight could overload these weak layers causing avalanches to occur.
Any snowpack collapses, whumpfing sounds, or shooting cracks represent signs of unstable snow. If you encounter any of these signs of instability, avoid NW-N-NE aspect avalanche terrain in the area.
Forecast Discussion
1 to 2 feet of snow can be found on NW-N-NE aspects above 8000' throughout the forecast region. Continuous snow cover starts around 7,200' to 8,000' along the Sierra Crest and 8000’ to 8500’ in the Carson Range. There is a high level of variability in the structure of the existing snowpack depending on elevation and location with concerning weak layers in some areas on NW-N-NE aspects. Generally, below 8000-8500' are a mix of rain crusts and faceted snow combinations. Areas above 8500' to 9000' are mostly all faceted snow and depth hoar with thinner or no rain crusts present.
Previous NE wind events scoured the upper portion of many wind exposed slopes down to rock, dirt, and/or ice before the recent snowfall. Despite this scouring, weaker faceted snow persisted on the lower portions of many slopes. A much thinner snowpack or bare ground exists across E-SE-S-SW-W aspects.
While the snowpack has become more usable for over the snow travel, there is still the potential to hit many obstacles (rocks, logs, open water, bushes, etc.) that are barely covered. Areas with a supportable rain crust are the most usable in the 7500’ to 8500’ elevation range. If you are traveling on snow for recreation, you should come up with a daily travel plan based on the current conditions and associated hazards. Anticipate encountering a different snowpack structure and a different set of travel conditions if you are moving from one place to another around the forecast area.
Media
Mountain Weather
- Issued
- Wednesday, December 6, 2023 - 6:43AM
- Author
- Steve Reynaud
An active weather pattern will enter our region this afternoon with increasing winds and snow. SW winds will continue to increase today and into the afternoon with ridge gusts over 100mph. Snowfall amounts have trended upwards from previous forecasts. Snow will begin late this afternoon with snow levels near 7500'. Snow levels will drop with heavy snow at times through the evening and night and will continue into and through Thursday. A winter weather advisory is in effect from 4pm this afternoon to 4pm Thursday afternoon. Colder and dryer conditions will start on Friday, with a slow warming trend into the weekend.
| Central Sierra Nevada | Conditions in the last 24hrs | Weather Forecast for Today Produced in partnership with the Reno NWS | Weather Forecast for Tonight Produced in partnership with the Reno NWS | Weather Forecast for Tomorrow Produced in partnership with the Reno NWS |
|---|---|---|---|---|
| Weather | Mostly sunny and clear. | Sunny then becoming partly cloudy. Rain and snow likely in the afternoon. Snow levels 7500 feet. Chance of precipitation is 70%. | Mostly cloudy. Snow in the evening, then chance of snow after midnight. 6500 feet decreasing to 6000 feet after midnight. Chance of precipitation is 85%. | Mostly cloudy. Snow likely through the day. Snow levels Below 5500 feet. Chance of precipitation is 70%. |
| Temperatures 7000 to 8000 ft. | @ 5am: 32 to 45 ° F | Max: 47 to 55° F | 42 to 47 ° F | 20 to 26 ° F | 28 to 33. ° F |
| Temperatures 8000 to 9000 ft. | @ 5am: 35 to 44° F | Max: 44 to 55° F | 38 to 44 ° F | 38 to 44. ° F | 24 to 30. ° F |
| Mid Slope Winds | South 10 to 15mph with gusts to 26mph. | Southwest 15 to 25 mph with gusts to 65 mph. | Southwest 15 to 30 mph with gusts to 60 mph. | Southwest 15 to 20 mph with gusts to 50 mph. |
| Ridgetop Winds | SW 30 t0 40mph with gusts to 49mph. | Southwest 30 to 50 mph increasing to 45 to 65 mph in the afternoon. | Southwest 30 to 50 mph increasing to 45 to 65 mph in the afternoon. | Southwest 30 to 50 mph. |
| Snowfall 7000 to 8000 ft. | 0 | 20% probability up to 2 inches. 80% probability no accumulation. | SWE = Up to 0.25 inch. | 70% probability of 2 to 8 inches. 30% probability of 7 to 9 inches. | SWE = Up to 0.60 inch. | 70% probability of 1 to 5 inches. 30% probability of 5 to 6 inches. | SWE = Up to 0.30 inch. |
| Snowfall 8000 to 9000 ft. | 0 | 40% probability up to 2 inches. 60% probability no accumulation. | SWE = Up to 0.25 inch. | 80% probability of 4 to 10 inches. 20% probability of 10 to 14 inches. | SWE = Up to 0.60 inch. | 40% probability of 1 to 5 inches. 60% probability of 6 to 10 inches. | SWE = Up to 0.30 inch. |
| Total Snow Depth between 8200 and 8700 ft. | 6 to 13 inches |
This information is provided by the U.S.D.A. Forest Service and describes general backcountry avalanche hazard and conditions.
It does not apply to ski areas and highways where avalanche mitigation is conducted.