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Avalanche Advisory for 2018-12-17 06:00
- EXPIRED ON December 18, 2018 @ 6:00 amPublished on December 17, 2018 @ 6:00 am
- Issued by Aaron Beverly - Mount Shasta Avalanche Center
Bottom Line
The avalanche danger is CONSIDERABLE near and above treeline due to potentially thick wind slabs. Avoid leeward slopes greater than 35 degrees. Loose dry avalanches near treeline are a secondary concern.
Avalanche Problem 1: Wind Slab
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Character ?
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Aspect/Elevation ?
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Likelihood ?CertainVery LikelyLikelyPossible
Unlikely -
Size ?HistoricVery LargeLargeSmall
The 13 inches of snow received over the last 24 hours coupled with 15-25 mph winds have most likely contributed to the formation of wind slabs. The new snow will continue to blow today. Expect these on northerly and easterly aspects but look for them everywhere. A widespread rain crust could provide the perfect bed surface for slabs to slide on. Use careful snowpack evaluation and conservative decision making toady. Stick to slopes under 35 degrees.
There is no clearer sign of unstable snow than recent avalanche activity. Pay attention out there. Winds slabs are often most sensitive to trigger immediately during or just after storm cycles. Look for blowing snow, wind pillows, shooting cracks and/or smooth, round, hollow sounding snow. Be suspicious of any steep slope with recent deposits of wind drifted snow. Weak layers could include old snow/new snow interfaces and/or density changes in the new snow.
Avalanche Problem 2: Loose Dry
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Character ?
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Aspect/Elevation ?
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Likelihood ?CertainVery LikelyLikelyPossible
Unlikely
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Size ?HistoricVery LargeLargeSmall
With 13 inches of new snow atop an often stout rain crust, keep an eye out for the loose-dry problem on slopes greater than 35 degrees. This type of avalanche starts at a point and entrains snow as it moves downhill. These "sluffs" are usually harmless but can catch an unaware skier and carry them into or over a terrain trap or down a long slope.
Loose-dry avalanches could be near treeline in areas protected by the wind.
Forecast Discussion
Snow below treeline was wet and heavy. With lower freezing levels last night and today, the snowpack below treeline should get locked up tight. Therefore avalanche danger below treeline is considered LOW.
Near and above treeline, avalanche danger is CONSIDERABLE. This means careful snowpack evaluation, cautious route-finding and conservative decision making are essential today. Natural avalanches are possible and human triggered avalanches are likely. You may encounter small avalanches in many areas, large avalanches in specific areas, or very large avalanches in isolated areas.
Recent Observations
Close to 13 inches of snow fell in the last 24 hours in the old ski bowl. Winds have been southerly and westerly averaging between 15 and 25 mph.
A tour up green butte ridge saw plenty of snow transport, though not much wind affect was seen on snow surfaces. Up to 7600 ft, snow was wet and heavy. Ski cuts of wind lips were unreactive. A widespread rain crust, stout in places, and breakable in others, that formed during Saturday's high snow levels, sat under 4-8 inches of moist to dry snow that was not well bonded to the crust. Limited visibility prevented any observations of the upper mountain. Columns tests yielded no notable results. The snowpack has a right side up configuration.
Weather and Current Conditions
Weather Summary
The effects of the front that brought close to 3 inches of water over the last three days will dissipate today giving us a break between storms. After effects may cause some lingering snow showers but little accumulation is expected. Another front moves in early tomorrow that could bring 2-4 inches at higher elevations. Winds are expected to crank above treeline. Snow levels will remain near 4500 ft today and tonight, rising to 5900 ft tomorrow.
24 Hour Weather Station Data @ 4:00 AM
| Weather Station | Temp (°F) | Wind (mi/hr) | Snow (in) | Comments | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cur | Min | Max | Avg | Avg | Max Gust | Dir | Depth | New | Water Equivalent | Settlement | ||
| Mt. Shasta City (3540 ft) | 38 | 37 | 42 | 40 | 3 | N | ||||||
| Sand Flat (6750 ft) | 29 | 29 | 33 | 32 | 33 | 7 | 1 | 1 | ||||
| Ski Bowl (7600 ft) | 21.5 | 21.5 | 31 | 28 | 45.2 | 12 | 2.48 | 0.9 | ||||
| Gray Butte (8000 ft) | 23.5 | 23.5 | 30.5 | 27.5 | 18 | 43 | S | |||||
| Castle Lake (5870 ft) | station down | |||||||||||
| Mount Eddy (6509 ft) | 22.5 | 22.5 | 33.5 | 31 | 1 | 18 | 247.5 | 0 | 0 | |||
| Ash Creek Bowl (7250 ft) | station down | |||||||||||
| Ash Creek Ridge (7895 ft) | station down |
Two Day Mountain Weather Forecast
Produced in partnership with the Medford NWS
| For 7000 ft to 9000 ft | |||
|---|---|---|---|
|
Monday (4 a.m. to 10 p.m.) |
Monday Night (10 p.m. to 4 a.m.) |
Tuesday (4 a.m. to 10 p.m.) |
|
| Weather | A 50 percent chance of snow showers. Mostly cloudy. | Snow. Temperature rising to around 33 by 4 a.m. Breezy and gusty. Chance of precipitation is 80%. | Snow before 4 p.m, then rain. Breezy and gusty. Chance of precipitation is 80%. |
| Temperature (°F) | 33 | 31 | 37 |
| Wind (mi/hr) | SW 5-10 | S 10-15 | S 15-20 |
| Precipitation SWE / Snowfall (in) | / < 1 | / 1-2 | / 3-4 |
| For 9000 ft to 11000 ft | |||
| Monday | Monday Night | Tuesday | |
| Weather | Snow showers likely, mainly between 10 a.m. and 4 p.m., then snow likely after 4 p.m. Mostly cloudy. Low wind chills. Windy and gusty. Chance of precipitation is 60%. | Snow. Windy and gusty. Chance of precipitation is 80%. | Snow. Low wind chills. Windy and gusty. Chance of precipitation is 80%. |
| Temperature (°F) | 27 | 25 | 27 |
| Wind (mi/hr) | SW 20-25 | W < 1 | W 45-50 |
| Precipitation SWE / Snowfall (in) | / < 1 | / 2-4 | / 3-5 |
Season Precipitation for Mount Shasta City
| Period | Measured (in) | Normal (in) | Percent of Normal (%) |
|---|---|---|---|
| From Oct 1, 2023 (the wet season) | 7.30 | 11.20 | 65 |
| Month to Date (since Apr 1, 2024) | 2.57 | 3.84 | 67 |
| Year to Date (since Jan 1, 2024) | 22.58 | 39.20 | 58 |
