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Avalanche Advisory for 2013-02-24 07:15:54

  • EXPIRED ON February 25, 2013 @ 7:15 am
    Published on February 24, 2013 @ 7:15 am
  • Issued by Nick Meyers - Shasta-Trinity National Forest

For today, the overall avalanche danger remains LOW with pockets of MODERATE danger where wind slabs are present. We received 5-7 inches of new snow over this past week with moderate to strong winds from various directions. Instabilities will be limited to areas of wind loading near ridgetops, bowls, rock outcrops, chutes and gullies. Winds have primarily blown from the northwest, however periods of wind from other directions have occurred. Be cautious of wind slabs on all aspects and on slopes steeper than 35 degrees.  Most other areas have been scoured down to the old, firm snow surface.

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

  • Character ?
  • Aspect/Elevation ?
  • Likelihood ?
    Very Likely
  • Size ?
    Very Large

Isolated areas hosting wind slabs will persist on most aspects, especially near and above treeline. Easy failures were found within wind slab layers in the past couple days. Slabs could be shallow to up to 2 feet thick. Failures propagated on layers of facets, below and above a buried, pencil hardness-crust layer, about 30-40 cm deep in snowpack, depending on wind slab thickness. Stability tests have shown easy failures with full propagation in wind loaded areas on these layers, but natural avalanches and/or human triggered avalanches have not been obeserved other than the Spring Hill slide in Avalanche Gulch on 2/20. Bottom line...the greatest instability will be limited to human travel on wind slabs near and above treeline on slopes steeper than 35 degrees.

Recent Observations

2-23-13  North side of Mt. Shasta, 4-8 inches new snow, wind affected. Traveled only to the trailhead, not in avalanche terrain. Several feet of snow at the trailhead and no recent tracks. Snowmobiles necessary for approx. 5 miles of road to access the trailhead. Very cold, poor visibility, snowing lightly at the time.

2-22-13  Mt Eddy area, NW aspect, 35 degree slope... ECTP 2 / Q1 - Failures on same layers as seen at Castle Lake...small, faceted snow crystals above and below buried crust layer, 30-40 cm deep in wind loaded area. Weakest layer has been below this crust layer. No recent nature/human triggered avys observed.

2-21-13 - Castle Lake area, NW aspect, 30 degree slope on Middle Peak... CT-6 / ECTP - 4 - Q1/2 -   Failures near buried crust on layer of facets, above old snow, about 30-40 cm down from surface, wind deposited snow, full propagation hard slab. No recent nature/human triggered avys observed.

2-20/2-21 - Numerous reports of "whoomfing" and shooting cracks near and above treeline on Mt. Shasta: Giddy Giddy gulch, Anaconda, The Promise Land areas.

2-20-13 - Avalanche Gulch, Spring Hill area, small wind slab avalanche (R1-D2), unknown trigger

Below: ECTP-4 / Q2 at Castle Lake on 2-21. Received same results (ECT-2) in Mt. Eddy area, wind loaded NW aspect.

    Weather and Current Conditions

    Weather Summary

    A clearing trend in general will begin today with high pressure building into the work week. Temperatures are slightly warmer this morning and will persist through the day, however another brief cold front is behind and temps will cool again late tonight. A slight disturbance will drop down into the area for Monday, but this storm is expected to be even weaker than the one we just had. I would expect snow levels to start near 5,000 feet and lower to 2,500 to 3,000... Precip totals look meager, around .01 inches of water....which probably means a trace of snow. Snow flurries could continue through Monday, though from the NWS discussion yesterday, "spring-like" conditions will ensue for the latter part of the week. Words that are not exactly music to a skiers ear...especially in February! Lastly, northwest flow will continue to bring us moderate to strong winds above treeline on the mountain, at least through Tuesday.

    WEATHER STATIONS - (last 24 hours):
    In Mt. Shasta City at 0500, we have clear skies and a current temperature of 27 F.
    On Mt. Shasta:  In the Old Ski Bowl (7,600') on the south side of Mt. Shasta, we have a current temperature of 16 F. Snow on the ground totals 100"  inches with no new snow and little settlement. Temperatures have ranged from 10 F to 27F.  At Grey Butte (8,000') on the south side of Mt. Shasta winds averaged 15 mph from the NW with a max gust of 71 mph from the NW. The current temperature is 24 F and temps have ranged 10 F to 25 F.
    Castle/Mt. Eddy:   Castle Lake - Castle Lake is hosting a current temp of 17 F. In the last 24 hours temperatures have ranged from 17 F to 29 F. Snow depth measures 47" inches with no new snow and little settlement.  On Mt Eddy, we have 66" inches of snow on the ground with no new snow and little settlement. The current temperature reads 23 F with temps ranging from 16 F to 24 F. Winds have been SE, averaging 5 mph and gusting to 17 mph from the SE.

    THIS SEASON:    A brief re-cap of the snow season thus far in Mt. Shasta... Leading up until now, September and October were warm and dry with September recording exactly zero precipitation. November remained warmer than normal with precipitation almost double normal values, 9.16" vs. 5.08". A local weather COOP observed the 2nd wettest November on record. December started out wet and warm, but temperatures cooled and brought snow to very low elevations. Since our avalanche cycle near Christmas, we've had a few small storms that brought some amounts of snow to the area, but did not produced any notable avalanches. January was below normal for precipitation with a long period of high pressure and sun that kept skiing conditions somewhat meager. We've had a few storms lately that has brought a pittance of wintery weather, but nothing to write home about!  The area has been under siege by high pressure overall giving us blue bird days for the most part. Feb 7/8 gave us up to 11" of new snow followed by moderate NE winds. Most recently, on 2-22 a trace to and inch of snow fell in the area. High and dry weather is expected for the next week and potentially the rest of the month. We currently have 6-10 feet of snow above 6,500 ft. Since September 1st, Mt Shasta sits at 78% of normal, 22.55" recorded; normal 28.81". For 2013, we sit at 14% of normal with 1.85" recorded and 12.93" normal.

    CURRENT CONDITIONS at Bunny Flat (6950 ft)
    0600 temperature: 11
    Max. temperature in the last 24 hours: 27
    Average wind direction during the last 24 hours: NW
    Average wind speed during the last 24 hours: 0-10 mi/hr
    Maximum wind gust in the last 24 hours: 14 mi/hr
    New snowfall in the last 24 hours: 0 inches
    Total snow depth: 63-100 inches

    Two Day Mountain Weather Forecast

    Produced in partnership with the Medford NWS

    For 7000 ft to 9000 ft
    (4 a.m. to 10 p.m.)
    Sunday Night
    (10 p.m. to 4 a.m.)
    (4 a.m. to 10 p.m.)
    Weather Mostly clear, cold this morning, warming throughout the day. Clear, cooling again late tonight Cool, slight disturbance to enter area in AM, weak system, snow flurries
    Temperature (°F) 38 Mid 21 29
    Wind (mi/hr) Northwest 10-15 mph Southwest 10-15 mph West/Northwest 10-20 mph
    Precipitation SWE / Snowfall (in) / 0 / trace / .5-1
    For 9000 ft to 11000 ft
      Sunday Sunday Night Monday
    Weather Mostly clear, windy Mostly clear, windy Snow flurries
    Temperature (°F) 30 13 19
    Wind (mi/hr) Northwest 35-40 mph with gusts higher Northwest/West 0 Northwest 40-50 mph with gusts higher
    Precipitation SWE / Snowfall (in) / 0 / trace / .5-1


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