The avalanche danger is LOW this morning but will increase to MODERATE on mid to upper elevation north facing slopes from the June Mountain area south to Rock Creek. Moderate to heavy snowfall and strong southwesterly winds will form additional storm and wind slabs in open terrain exposed to the wind. Expect to find fresh wind slabs along and below north to easterly facing ridgelines and on exposed mid-slope features such as ribs and breakovers. This advisory will be updated later today as the main part of the storm reaches the area.
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Above Treeline
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Near Treeline
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Below Treeline
The main avalanche problem today is recently formed slabs of wind transported snow in exposed terrain. A combination of new snow and wind from yesterday evening through the night and this morning has likely caused the first round of storm slab formation. Expect these fresh drifts to be sensitive on many slopes. Continued snowfall and strong southwesterly winds, wind loading will become increasingly common and dangerous as the day progresses.
In Rock Creek, stability tests continue to show the depth hoar layer at the bottom of the snowpack is still reacting in sudden collapse failures on north facing slopes. The weather forecast calls for snow accumulations over the next 5 days of up to 2 feet. While Rock Creek may not receive 2 feet of new snow, additional loading will increase the load on these widespread weak layers.
The recent dry spell left us with a variety of old snow surfaces. One observer called south facing slopes on Mono Pass "aerated crunchy stuff". Exposed east facing slopes above 10,000 ft. in the June Mountain area were a mix of icy early satrugi. On high elevation north facing slopes, small facets formed widespread weak surface layers that will be buried under today's snowfall, and more snowfall is in the forecast today and tonight. So far this is not an avalanche problem but as a soft slab builds atop this new weak layer, this will change today. Today and tomorrow, use increasing caution on slopes approaching 35 degrees and watch for a developing storm slab instability that could produce shallow slabs or sluffs.
Reports of poor snow stability continue to come in from the Rock Creek area. Sudden collapse on large depth hoar continue to be reported in Rock Creek on north facing slopes above 9,600 ft. Depending on the amount of water content of the new snow, additional loading of this weak snowpack could create dangerous avalanche conditions due to persistent buried weak layers.
Observations from a snowpit dug at 11,400 ft near Half Moon Pass in Rock Creek reported up to 5 to 6 ft. of snow on the north facing slopes. The same crusts from a month earlier were still evident and a 3 cm surface crust had over 2 inches of facets below the crust. There was 4 to 8 inches of depth hoar at the bottom but compression tests and a Rutschblock test yielded test scores in the 28-29 range for compression tests, an ECT (ECTX)and an RB7 score.
Above Lake Mary yesterday, there was near surface facets on shaded north facing slopes at 9,800 ft. and a thin layer of large solid facets on the ground that did not react in extended column tests.
Snow is falling this morning and will continue to fall all day. Periods of heavy snow will occur later today as the storm moves on shore. Wind gusts over 50 mph are expected over the mid elevations. Winds will be out of the southwest today, gusting to over 50 mph at the mid elevations.
Snow showers continue tomorrow. A more powerful storm reaches the eastern Sierra this weekend with over a foot of snow expected in the mountains. Another storm is epected to drop another foot of snow over the area by Tuesday.
Expect cool late winter weather for at least a week. Highs will be in the upper 20's to the low 30's with lows in the teens and upper 20's.
| 0600 temperature: | 18 deg. F. |
| Max. temperature in the last 24 hours: | 42 deg. F. |
| Average wind direction during the last 24 hours: | WSW |
| Average wind speed during the last 24 hours: | 60-70 mph |
| Maximum wind gust in the last 24 hours: | 75 mph |
| New snowfall in the last 24 hours: | 3 inches |
| Total snow depth: | 40 inches |
| Wednesday | Wednesday Night | Thursday | |
|---|---|---|---|
| Weather: | snow | snow | chance of snow |
| Temperatures: | 29 deg. F. | 16 deg. F. | 31 deg. F. |
| Wind Direction: | SW | SW | West |
| Wind Speed: | 30-35 | 25-35 | 20-30 |
| Expected snowfall: | 3-4 in. | 1-2 in. | 1 in. |
| Wednesday | Wednesday Night | Thursday | |
|---|---|---|---|
| Weather: | snow | snow | chance of snow |
| Temperatures: | 28 deg. F. | 16 deg. F. | 31 deg. F. |
| Wind Direction: | SW | West | SW |
| Wind Speed: | 30-40 | 30-35 | 30-45 |
| Expected snowfall: | 1-3 in. | 1 in. | 1 in. |
