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Avalanche Advisory for 2016-01-29 06:52:38
- EXPIRED ON January 30, 2016 @ 6:52 amPublished on January 29, 2016 @ 6:52 am
- Issued by Jon Dove - Shasta-Trinity National Forest
Bottom Line
Overall, MODERATE avalanche danger exists near and above treeline on all aspects for newly developing wind and storm slabs. LOW avalanche danger exists below treeline. Avalanche danger will increase at all elevations with the current storm. Some unstable snow could exist on isolated terrain features. Evaluate snow and terrain carefully; identify features of 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
Today's storm and strong west/southwest winds will develop new wind slab formations near and above treeline. Wind slabs small to medium in size will form in the usual locations just below ridge tops, the tops of chutes and couloirs, depressions around rock outcroppings, and in gullies. The strength of the winds may also transport and deposit snow in non-typical mid-slope locations, as well. Ridge tops will be scoured down to firm, old snow surfaces and cornices will build in size. Snow levels with this system have hung around 6,000-6,500 ft., but will lower as the system progresses with a cold air mass pushing it along. The most likely place to find and trigger a wind slab today will be on slopes 35 degrees and steeper, in complex terrain, steep chutes, convexities/roll overs, and cross loaded depressions. Slabs will build in size and depth primarily on leeward NW-N-NE-E-SE-S aspects with some possible cross loading on W-SW aspects with today's strong west/southwest winds.
Avalanche Problem 2: Storm Slab
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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
Storm slabs have the potential to develop at all elevations with today's storm system and the associated cold air mass driving it across the region. The strong west/southwest winds will limit the amount of storm slab development above treeline. Storm slabs will still be a concern, however, with the significant amount of snow forecast for elevations above the snow line (6,500 ft. falling to around 4,000 by tonight).
Forecast Discussion
Precipitation amounts received yesterday fell below what was predicted with the majority falling before noon. Mostly cloudy skies prevailed for the remainder of the day with an occasional peek through to the blue skies above. Precipitation did not resume until after midnight last night. Snow levels with yesterday's storm rose to around 7,000 ft. before tappering off in the early afternoon. A much colder air mass will move in behind the cold front lurking just off shore which will help to lower snow levels as the day progresses. Levels will drop to 3,500-4,000 ft. by Saturday morning. The pressure gradient over the area will be tight enough during this weather system to push winds to advisory levels. Winds above treeline, at mid-mountain levels (10,000 ft.) will be there strongest during today's storm at 60-65 mph with gusts pushing into hurricane force. Winds will begin to lower slightly overnight, continuing to drop on Saturday to 20-30 mph prevailing out of the west-southwest.
THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 21.68 inches of water, normal is 21.64 inches, putting us at 100% of normal. For the month of January and year of 2016 we've received 12.19 inches of water, normal is 6.43 inches, putting us at 189% of normal .
Recent Observations
Yesterday's storm was not quite as wet as had been expected with the majority of precipitation falling before noon totaling 0.15 inches of water. The current storm system began to ramp up after midnight with predicted total water amounts falling just above 1 inch of water. The strongest pulse of precipitation is forecast to occur this morning with showers tapering off this afternoon to early evening. Snow conditions yesterday near and below treeline were soft and heavy as one might expect with the warm temperatures and a mix of rain and snow. The afternoon was characterized by mostly cloudy skies with the occasional break allowing a few rays of sun to penetrate through. This allowed the snowpack to continue to consolidate over the course of the day near and below treeline. Above treeline, snow fell adding a few more inches on top of a firm surface from the previous few days of clear skies and moderate temperatures. An extended column test was performed on a SE aspect just below treeline on a 31 degree slope resulting in a score of ECTX.
For today, avalanche danger will remain low below and near treeline due to the few days of sunshine, warmer temperatures, and then some rain/wet snow yesterday morning. It will, however, rise with the development of wind and storm slabs resulting from today's storm which has already added a couple of inches of new snow this morning. For above treeline, avalanche danger has edged back up to moderate once again due to another round of wind and storm slab formation.
Quick Pit Profile from West aspect in Sun Bowl on 1-27-2016 by Jon Dove:
View across Sun Bowl to SE aspect. Note the two small naturally triggered wind slab avalanches with starting zones directly below cornice formations:
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LOCAL AREA ROAD, NORDIC and SNOWMOBILE PARK STATUS:
The Sand Flat cross country ski trails are in great shape and ready for your cross country skis or snow shoes. These are backcountry trails marked with blue diamonds on trees. Trails are not groomed. Snow shoers, please blaze a parallel trail to cross country skiers staying out of the skin track. These trails can be accessed via the Everett Memorial Highway. Thank you, and enjoy!
The Mt Shasta Nordic Center is open! These beautiful, groomed trails can be accessed via the Ski Park Highway. http://www.mtshastanordic.org
The Pilgrim Creek & Deer Mountain Snowmobile Parks are open! Trails are being groomed currently. Head to our "Education" tab on our website and find the snowmobile section for trail information, grooming status and other sledder resources!
The Castle Lake road is plowed to the lake. The Everett Memorial Highway is plowed to Bunny Flat.
The Five Red Flags of Avalanche Danger any time of year include: 1) Recent/current avalanche activity 2) Whumphing sounds or shooting cracks 3) Recent/current heavy snowfall 4) Strong winds transporting snow 5) Rapid warming or rain on snow.
Weather and Current Conditions
Weather Summary
Good Morning! In Mt Shasta City at 0500, we have a current temperature of 43 F, two degrees cooler than yesterday at this time. Skies are cloudy with light rain.
On Mt Shasta (South Side) in the last 24 hours...
Old Ski Bowl - 7,600 feet, the current temperature is 28 degrees F. Snow on the ground totals 118 inches with 1 inch new snow and no settlement. Temperatures have ranged from 25 F to 35 F.
Grey Butte - 8,000 feet, the current temperature is 27 degrees F. Temperatures have ranged from 26 F to 33 F. Winds have been averaging 10-15 mph, with a max gust to 35 mph, west.
Mt Eddy Range (West side of Interstate-5)...
Castle Lake - 5,600 feet, the current temperature is 35 degrees. Temperatures have ranged from 34 F to 44 F. Snow on the ground totals 65 inches with no new snow and 1 inch of settlement.
Mt Eddy - 6,500 feet, the current temperature is 31 degrees F. Temperatures have ranged from 25 F to 40 F. Snow on the ground measures 82 inches with no new snow and 2 inches of settlement. Winds have averaged 2 mph, south/southeast with a max gust of 11 mph, southeast.
Always check the weather before you attempt to climb Mt Shasta. Further, monitor the weather as you climb. Becoming caught on the mountain in any type of weather can compromise life and limb. Be prepared.
| 0600 temperature: | 32 |
| Max. temperature in the last 24 hours: | 37 |
| Average wind direction during the last 24 hours: | Westerly |
| Average wind speed during the last 24 hours: | 10-15 mi/hr |
| Maximum wind gust in the last 24 hours: | 35 mi/hr |
| New snowfall in the last 24 hours: | 2 inches |
| Total snow depth: | 96 inches |
Two Day Mountain Weather Forecast
Produced in partnership with the Medford NWS
| For 7000 ft to 9000 ft | |||
|---|---|---|---|
|
Friday (4 a.m. to 10 p.m.) |
Friday Night (10 p.m. to 4 a.m.) |
Saturday (4 a.m. to 10 p.m.) |
|
| Weather | Cloudy. Rain before 10 am, then rain and snow between 10 am and 1 pm, then snow after 1 pm. Windy | Mostly cloudy with a 70% chance of precip. Snow showers likely before 10 pm, then a slight chance of snow showers after 4 am. Breezy | Mostly cloudy. 70% chance of precip. Slight chance of snow showers in the morning, then snow showers likely in the afternoon. |
| Temperature (°F) | 38 | 22 | 28 |
| Wind (mi/hr) | Southwest 20-30 mph with gust to 65 mph decreasing to 15 mph with gusts to 45 mph in the afternoon | West 10-15 mph | Southwest 5-10 mph |
| Precipitation SWE / Snowfall (in) | / 1-2 | / 0-1 | / 0-1 |
| For 9000 ft to 11000 ft | |||
| Friday | Friday Night | Saturday | |
| Weather | Cloudy. Snow, could be heavy at times. Windy with wind chill values as low as -10. | Mostly cloudy with a 70% chance of precip. Snow showers likely before 10 pm, then a slight chance of snow showers after 4 am. Windy with wind chill values as low as -22. | Cloudy, then gradually becoming mostly sunny. 70% chance of precip. Snow showers likely, mainly between 10 am and 4 pm. Windy with wind chill values as low as -23. |
| Temperature (°F) | 25 | 4 | 4 |
| Wind (mi/hr) | West 60-65 mph with higher gusts | West 6-10 | West 20-25 mph with higher gusts |
| Precipitation SWE / Snowfall (in) | / 6-10 | / 0-.5 | / 2-4 |
