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Avalanche Advisory for 2017-02-24 06:23:14

  • EXPIRED ON February 25, 2017 @ 6:23 am
    Published on February 24, 2017 @ 6:23 am
  • Issued by Nick Meyers - Shasta-Trinity National Forest

The overall avalanche danger is MODERATE today, near treeline and above treeline. The most dangerous places are at mid and upper mountain levels where new, light density snow has or will be wind transported onto leeward ridgelines and tops of bowls. If you see blowing snow, pay attention to wind direction and where that snow is headed! If you avoid these leeward slopes, you will avoid being in avalanche danger today.  Below treeline, the avalanche danger is LOW.

 

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Avalanche Problem 1: Wind Slab

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Human triggered wind slabs will remain possible today near treeline and above treeline. Most wind slabs will shallow but could propagate across a large area. Ridgelines on the upper mountain will see the most wind today. Use clues such as blowing snow to help identify recently wind-loaded slopes where unstable wind slabs may exist.

 

Avalanche Problem 2: Cornice

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Small to large cornices have been observed in the forecast area. Some of these cornices, upon failure, have triggered wind slabs on slopes below. The chance of this occurring is becoming less so, but continue to keep this in mind as you are traveling along ridgelines or anywhere cornice formations are observed. Most cornices have been observed on the west side of I-5 in the Eddy Range. We have yet to get up to Castle Lake recently.

 

 

Avalanche Problem 3: Loose Dry

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Small, loose snow sluffs that involve the cold unconsolidated snow that exists in the upper foot of the snowpack could be possible today on steep sheltered slopes. Most of these would occur where the coldest and least cohesive snow exists on NW-N-NE-E aspects below and near treeline. It is not expected for these avalanches to be a serious threat. Several small, loose dry slides were observed yesterday near treeline on Mt Shasta. They were initiated by falling rime ice.

 

Forecast Discussion

Overall, the snow stability in the Mt Shasta area backcountry is looking pretty good. Concern lies for any new wind transport of our 4-6 inches of light density snow that sits at the top of the snowpack. New wind slabs on leeward slopes will be the top concern for any riders or sliders in the backcountry today.

 

Recent Observations

Observations were made over a widespread area on the south side of Mt Shasta yesterday including the Bunny Flat area, Old Ski Bowl up to 10,000 feet and the Gray Butte area. Every once in a while during a storm, temperatures and wind will drop and the result is pretty magical. Overall, about 4-6 inches of new, light density snow fell upon the forecast area and provided for some very smooth and silky snow surface conditions in all areas.  It was the unadulterated above treeline terrain that was most notable. The day brought periods of warm February sun quickly followed with light snow showers and partly cloudy skies. Above 9,000 feet, soft snow prevailed but ridgelines remained somewhat scoured and snow surfaces were like styrofoam. Down in gullies and lower lying areas held soft, very light new snow on top of supportable, one finger hand hardness, older snow. One small, new wind slab avalanche occurred late in the day in Sun Bowl. I noticed this as I was leaving Bunny Flat. It's unknown if it was a natural or human triggered slide. The crown was maybe 6-8 inches deep, 100 feet wide and ran only half the length of the bowl. A few older debris piles and crown lines were visible off the east and north aspects of Green Butte and the west aspect of Red Butte. Sunny, southerly slopes below 8,500 feet had some small roller ball action. Winds were almost dead calm for most of the day and temperatures were in the mid to high teens at 8,000 feet. Later in the day, a thin, breakable zipper crust began to form on sun exposed slopes below 7,500 feet. I dug a full pit on a NE aspect at 7,700 feet and could not get any notable results trending toward unstable snow or lingering weak layers.

Weather and Current Conditions

Weather Summary

It is a chilly one this morning! Unseasonably cold temperatures for this time of year will continue through the weekend. In fact, this mornings weather balloon launch set a record for the 850mb (5,000ft) temperature. The average for late February is about 35F. This mornings launch out of the NWS Medford was 20F! We've got two low pressure systems that will deliver a couple inches of new snow over the next several days. The first will arrive late this afternoon. Expect about .18" of snow/water equivalent, or about 1-2 inches of snow, with snow levels to town and lower. Tomorrow will remain partly cloudy with perhaps a bit of sun. Sunday into Monday will bring the second low pressure system. About a quarter inch of water (2-4 inches snow) is expected with this storm with continued low snow levels. For the next couple days, winds look quite calm below and near treeline. Above treeline doesn't look to bad either, however the upper mountain will likely see windy conditions. 

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In Mt Shasta City at 0500, we have a current temperature of 11 F.

On Mt Shasta (South Side) in the last 24 hours...

All weather stations are currently down. We are trouble shooting the issue.

THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 43.23 inches of water, normal is 28.14 inches, putting us at 153% of normal.  For the month of February, we have received 10.97 inches of water, normal is 5.87, which is 186% of normal. And finally for the year of 2017, we received 22.07 inches of water, normal is 12.93 inches, putting us at 170% of normal.

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.

CURRENT CONDITIONS at Bunny Flat (6950 ft)
0600 temperature: 11
Max. temperature in the last 24 hours: 35
Average wind direction during the last 24 hours: Variable
Average wind speed during the last 24 hours: 0-5 mi/hr
Maximum wind gust in the last 24 hours: 5-10 mi/hr
New snowfall in the last 24 hours: 0 inches
Total snow depth: 122 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 Snow showers, mainly after 4pm. Wind chill values as low as zero. Chance of precipitation is 80%. Snow showers. Chance of precipitation is 80%. A 50 percent chance of snow showers. Partly sunny.
Temperature (°F) 22 14 25
Wind (mi/hr) East/Southeast becoming south/southwest in the afternoon. 5-10 mph South, becoming east after midnight 5-10 mph North 5-10 mph
Precipitation SWE / Snowfall (in) / 0-1 / 2-4 / 0-.5
For 9000 ft to 11000 ft
  Friday Friday Night Saturday
Weather A 20 percent chance of snow showers after 10am. Increasing clouds and cold. Wind chill values as low as -26. Windy on the upper mountain. Snow showers likely. Cloudy. Wind chill values as low as -21. Chance of precipitation is 70%. A 50 percent chance of snow showers. Partly sunny and cold. Wind chill values as low as -15.
Temperature (°F) 2 1 5
Wind (mi/hr) West/Southwest 5-10 mph Southwest 0-1 North 5-10 mph
Precipitation SWE / Snowfall (in) / 0-1 / 2-4 / 0-.5

Disclaimer

This advisory does not apply to Ski Areas or Highways and is for the Mt. Shasta, Castle Lake and Mt. Eddy backcountry. Use this information for guidance only. You may find different conditions in the backcountry and should travel accordingly. This advisory expires on midnight of the date it was posted unless otherwise noted.