Backcountry Avalanche Forecast Central Sierra Nevada
Sierra Avalanche Center
www.sierraavalanchecenter.org
- Issued
- Tuesday, December 12, 2023 - 6:45AM
- Expires
- Wednesday, December 13, 2023 - 6:45AM
- Author
- Steve Reynaud
The Bottom Line
A weak and shallow snowpack exists below the recent storm snow we received last week. Where strong wind blown or consolidated snow sits on top of this weak snow, avalanches remain possible. Early season conditions with rocky and shallow snowpack areas continue throughout the forecast region.
Avalanche Danger
Tuesday, December 12, 2023
Wednesday, December 13, 2023
- Above Treeline2 - Moderate
- Near Treeline2 - Moderate
- Below Treeline2 - Moderate
 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 (1)
Problem #1: Persistent Slab
Problem Type
Aspect/Elevation
Likelihood
Size
Weak faceted snow below the recent storm snow. Northern side of Hourglass Bowl. Tamarack Peak, Mt. Rose area.
Photo: SACA weak faceted snowpack exists on many NW-N-NE aspects throughout the forecast region. The most recent storm snow has not been enough load to cause avalanches on this weak layer up to this point, with a high level of variability in the weak layer and overlying slab strength depending on location. Snowpack tests still continue to show unstable results on multiple layers in our snowpack at some locations. Areas with wind blown snow or consolidated recent storm snow on top of this weak snowpack structure, are the most concerning areas for a persistent slab avalanche to occur.
If a persistent slab avalanche did occur, it could break wider than expected and be remotely triggered. Any signs of instability encountered (shooting cracks, whumpfing sounds, snowpack collapses) would mean that you are in a location that has all the ingredients for a persistent slab avalanche to occur. If an avalanche did occur, it could result in serious trauma from all the exposed rocks and current shallow snowpack.
Forecast Discussion
A weak faceted (sugary) snowpack exists on most NW-N-NE aspects. As elevation increases expect to find layers of faceted snow in between rain crusts. Above about 8,500', rain crusts disappear and the snowpack becomes nearly all weak faceted snow. Generally speaking, the higher up you go on wind protected NW-N-NE aspects, the weaker the snowpack. Early season NE wind events previously scoured some exposed slopes down to dirt, rock, or ice. The distribution and strength of the faceted snowpack varies greatly throughout the forecast region.
Cold temperatures, clear skies, low sun angles, and long nights will continue the faceting process in our shallow snowpack further decreasing the snowpack structure.
There is still the potential to hit many obstacles (rocks, logs, open water, bushes, etc.) that are barely covered (or not) by the shallow snowpack. Areas with a supportable mid snowpack rain crust in the 7,500’ to 8,500’ elevation range provide the most usable snowpack. 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
- Tuesday, December 12, 2023 - 6:27AM
- Author
- Steve Reynaud
Cooler temperatures with continued dry conditions and mostly sunny skies will continue through this week. Winds have shifted to the NE last night and will increase in speed this afternoon continuing through Wednesday. These winds will bring in cooler temperatures and help to mix out the recent valley inversions.
| 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 | Partly cloudy. | Sunny. Snow levels 5500 feet. Chance of precipitation is 5%. | Clear then becoming partly cloudy. Snow levels 5500 feet. Chance of precipitation is 5%. | Sunny. Snow levels 5500 feet. Chance of precipitation is 5%. |
| Temperatures 7000 to 8000 ft. | @ 5am: 19 to 38° F | Max: 42 to 49° F | 33 to 38. ° F | 17 to 23. ° F | 34 to 40. ° F |
| Temperatures 8000 to 9000 ft. | @ 5am: 25 to 33° F | Max: 36 to 48° F | 29 to 35. ° F | 16 to 22. ° F | 31 to 37. ° F |
| Mid Slope Winds | Light winds | Light winds becoming northeast around 15 mph with gusts to 30 mph in the afternoon. | East around 15 mph with gusts to 35 mph. | Light winds. |
| Ridgetop Winds | West switching to NE at 10 to 15mph with gusts to 21mph. | Northeast around 15 mph. Gusts up to 35 mph. | East 15 to 30 mph with gusts to 50 mph. | East 15 to 25 mph with gusts to 40 mph. |
| Snowfall 7000 to 8000 ft. | 0 | No accumulation. | SWE = None. | No accumulation. | SWE = None. | No accumulation. | SWE = None. |
| Snowfall 8000 to 9000 ft. | 0 | No accumulation. | SWE = None. | No accumulation. | SWE = None. | No accumulation. | SWE = None. |
| Total Snow Depth between 8200 and 8700 ft. | 8 to 23 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.