THIS AVALANCHE FORECAST EXPIRED ON March 17, 2020 @ 6:53 am
Avalanche Forecast published on March 16, 2020 @ 6:53 am
Issued by Brandon Schwartz - Tahoe National Forest

Dangerous avalanche conditions continue in the backcountry at all elevations with wind slab, storm slab, and deep slab avalanche problems. Terrain and route selections should be made deliberately and conservatively with the specific intention to manage today's avalanche problems. Avalanche danger is CONSIDERABLE at all elevations.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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As of this writing, ridgetop wind speeds remain strong out of the S to SW and have yet to decrease as forecast. A shift to SE and a decease to moderate speed is expected today. This should decrease drifting and new wind slab formation as compared to the past 36 hours. Continued instability of wind slabs formed yesterday and last night remains the major concern above treeline and near treeline on NW-N-NE-E-SE-S aspects. Avalanche size on these aspects is expected mostly at D2 with up to D3 possible today. Once the forecast wind shift occurs, smaller wind slabs may form near treeline and above treeline on SW-W aspects that held previous snow cover.

Identify cornices and pillows of wind drifted snow. Wind slabs are on the slopes below these features. Route find around these areas and do not linger below them. Avoidance is a better tactic today than trying to determine if wind slabs are stable or unstable.

Avalanche Problem 2: Storm Slab
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Ongoing snowfall is continuing to introduce new weak layers within the storm snow. Warming air temperatures today may create an upside-down storm slab layer in the upper snowpack. This will keep a storm slab avalanche problem ongoing today in wind protected areas near treeline and below treeline on all aspects. With 2 to 5 feet of new snow in most areas, anchoring does not exit for upper snowpack storm slabs in the areas that had little to no previous snow cover.

Use snow surface cracking triggered while breaking trail as a clue to the presence of this avalanche problem. Specifically choose terrain and routes that give you options for avoiding avalanche terrain if storm slab instability is present.

Avalanche Problem 3: Deep Slab
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In many areas, feet of new snow has been loaded on top of weak faceted (sugary) snow a few inches below the old/new snow interface near treeline and below treeline on NW-N-NE aspects. This has created a deep slab avalanche problem with an expected avalanche size of D2 to D3. Any deep slab avalanches will involve all of the accumulated new snow, plus the additional depth of wind drifted snow if occurring near treeline. Very large avalanches may occur in below treeline areas on slopes with a history very infrequent avalanches.

Becoming caught in a deep slab avalanche near or below treeline may not be survivable. If you hear a whumph or experience snowpack collapse, unstable snow associated with this problem is present in the immediate area and an avalanche would have just occurred if the slope were steeper. Practical ways to avoid this avalanche problem are aspect avoidance or conservative terrain selection.

recent observations
Submit Observations

* Due to the high danger level yesterday and numerous road closures, observations were collected in very conservative terrain. On Donner Ridge (Donner Summit area) fragile cornices and wind slab avalanches up to 10 inches deep were intentionally skier triggered on test slopes along the ridgetop. Multiple layers of wind slab were noted on these test slopes. Digging a snowpit in wind protected terrain below treeline on a N aspect at 7,720' we unintentionally collapsed the facet layer just below the old/new snow interface with deep foot penetration. An audible whumph and a visible drop of the snow surface with this collapse gave evidence of the suspected deep slab avalanche problem.

* Other observations submitted from around the forecast area, also from conservative terrain gave indications of weakness within the new snow and possible storm slabs.

Weather and CURRENT CONDITIONS
weather summary

The storm system that has already brought 2.5 to 5 feet of new snow to the forecast area over the past two days continues. Snowfall rates are forecast to decrease today to 1 inch per hour or less, but significant ongoing new snow accumulation is expected. Ridgetop winds are expected to shift to the SE this morning. Wind speeds are forecast to decrease to moderate speed on the ridgetops today. With the shift in wind direction will come about 5 degrees of warming for today as compared to yesterday. Snow levels are forecast to rise up to near 6,000' today, especially during periods of decreased snowfall intensity. This may be most prominent along the eastern side of the forecast area.

CONDITIONS ALONG THE SIERRA CREST BETWEEN 8200 FT. AND 9200 FT. IN THE LAST 24 HOURS
Weather Station Map
Weather Station Table
6am temperature: 18 to 24 deg. F.
Max. temperature: 20 to 26 deg. F.
Average ridgetop wind direction: SW
Average ridgetop wind speed: 42 mph
Maximum ridgetop wind gust: 113 mph
New snowfall: 14 to 20 inches
Total snow depth: 61 to 95 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 7000 ft. to 8000 ft.
Monday Monday Night Tuesday
Weather: Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 90%. Cloudy. Snow in the evening, then chance of snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 85%. Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 40%.
Temperatures: 30 to 35. deg. F. 15 to 20. deg. F. 28 to 33. deg. F.
Mid Slope Winds: Southeast around 15 mph with gusts to 25 mph. Light winds. Gusts up to 25 mph after midnight. Light winds becoming southwest around 15 mph in the afternoon. Gusts up to 25 mph.
Expected snowfall: 70% probability of 6 to 10 inches. 30% probability of 4 to 6 inches. | SWE = 0.40-0.65 inch. 80% probability of 2 to 6 inches. 20% probability of 6 to 9 inches. | SWE = 0.20-0.40 inch. Up to 2 inches. | SWE = less than 0.10 inch.
For 8000 ft. to 9000 ft.
Monday Monday Night Tuesday
Weather: Cloudy. Snow. Snow levels below 7000 feet. Chance of precipitation is 95%. Cloudy. Snow in the evening, then chance of snow after midnight. Snow levels below 7000 feet. Chance of precipitation is 90%. Mostly cloudy. Chance of snow. Snow levels below 7000 feet. Chance of precipitation is 40%.
Temperatures: 25 to 30. deg. F. 11 to 16. deg. F. 22 to 28. deg. F.
Ridge Top Winds: Southeast 15 to 25 mph with gusts to 40 mph. Southwest around 15 mph with gusts to 25 mph. Southwest 15 to 20 mph with gusts to 30 mph.
Expected snowfall: 70% probability of 6 to 10 inches. 30% probability of 4 to 6 inches. | SWE = 0.40-0.65 inch. 80% probability of 2 to 6 inches. 20% probability of 6 to 10 inches. | SWE = 0.20-0.45 inch. Up to 2 inches. | SWE = less than 0.10 inch.
Disclaimer

This avalanche forecast is provided through a partnership between the Tahoe National Forest and the Sierra Avalanche Center. This forecast 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 forecast applies only to backcountry areas outside established ski area boundaries. This forecast describes general avalanche conditions and local variations always occur. This forecast expires 24 hours after the posted time unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.

For a recorded version of the avalanche forecast call (530) 587-3558 x258