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Avalanche Advisory for 2016-03-23 07:08:35
- EXPIRED ON March 24, 2016 @ 7:08 amPublished on March 23, 2016 @ 7:08 am
- Issued by Nick Meyers - Shasta-Trinity National Forest
Bottom Line
MODERATE avalanche danger overall, with areas of CONSIDERABLE danger, exist near and above treeline today for wind slab avalanches. Recent new snow and wind blowing from both the N/NW and S/SW has loaded leeward terrain near ridgetops and bowls. A human triggered avalanche is possible today, and likely in wind loaded, steep terrain. You need to be able to identify wind loaded terrain and take appropriate action to avoid triggering an avalanche.
Avalanche Problem 1: Wind Slab
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Likelihood ?CertainVery LikelyLikelyPossible
Unlikely -
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We've seen moderate to strong wind all over the board in the last three days, blowing from the north/northwest/west and also the southwest/south/southeast. This has created soft to hard wind slabs on many aspects near and above treeline in the forecast area. Temperatures have struggled to rise above freezing. Even though the sky might be blue, snow being transported by wind and loading onto leeward terrain can still produce unstable conditions and possibly an avalanche. About 7-12 inches of new, fairly light density snow fell over the region above 6,500 feet. Immediately during and after the storm, weakensses within the new snow were easily triggerable on small test slopes. I would suspect that slabs are still lingering near and above treeline and could be sensitive to human trigger. I would be cautious of terrain near ridgelines where wind loading has taken place. Do you see blowing snow? Have you quickly skied onto snow of different density? Does the snow look scalloped or like a big snow pillow? Pay attention to these signs that wind is or has been present. Areas of instability may also exist on cross loaded slopes and perhaps mid-slope depressions or leeward convexitites of moraines. The bonding of the new snow to old snow has been good... weak layers will lie within the new snow. A slight change in temperature, wind direction, or wind speed can create density changes in the snowpack and function as a weak layer.
Avalanche Problem 2: Loose Dry
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Likelihood ?CertainVery LikelyLikelyPossible
Unlikely
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Size ?HistoricVery LargeLargeSmall
While not a big concern, loose dry sluffs within new snow layers on steep (>37 degrees), north facing slopes are possible today. Light density snow that has preserved will likely sluff, but it is not expected for them to gain enough size to cause harm to human life. Always be cautious with loose sluffs as they can catch you off guard, potentially sweep you off your feet, and push you into a tree or other terrain traps.
Forecast Discussion
High pressure will keep things dry today, however a weak front will move on shore late tonight. This front is not expected to provide much precipitation, if any at all. We'll move back into northwesterly flow as the weekend approaches and then another cool system (as in temperature...) for Easter Sunday will move through. Both of these said weak fronts will result most likely in increased cloud cover at best and perhaps a few hundredths of an inch of water where good upslope effects are present. Next week an overall drying trend will finish off March for us. Winds look to be light to moderate for the remainder of the week. Max winds will reach 30-40 mph in exposed areas and average 20-30 mph at mid-mountain levels. Below treeline, wind speeds will be calm and quite civilized.
THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 36.72 inches of water, normal is 34.20 inches, putting us at 107% of normal. For the month of March we've received 11.20 inches of water, normal is 4.70 inches, putting us at 238% of normal, and finally... for the year of 2016 we've received 27.23 inches of water, normal is 18.99 inches, putting us at 143% of normal.
Recent Observations
A decent dollop of new snow fell over the first part of the week bringing on average 7-12 inches of fairly light density new snow to avalanche terrain in the forecast area. This storm was relatively cool. Temperatures rose a bit yesterday, but struggled to reach above freezing on the mountain. Areas like Castle Lake did climb above freezing. Winds have been moderate to strong, blowing both out of the south/southwest and also the northwest. These winds have certainly been blowing snow around and loading many leeward aspects. A local rider reported yesterday that the visibility was poor, but still was able to observe what looked to be like a 20 to 30 foot wide soft slab release in Sun Bowl on the south side of Mt Shasta. The crown depth is unknown, but he added that it ran about 3/4 of the way down the bowl. It's suspected that this was a natural trigger, wind loading from the steady northwest winds we saw yesterday. For much of the day, the northwesterlies averaged 20-30 mph with gusts into the 40 mph range. Sun Bowl is a classic slide path that recieves a lot of wind loading during northwest wind events. Some other local riders reported decent skiing conditions, albeit a bit of a thin crust on top of the snow. Perhaps a bit of a sun crust formed on southerly aspects it sounds like. Even though the storm has passed this week and we've had a couple days for the snow to settle, windy conditions above treeline continue to transport snow. Temperatures will persist and remain cool. Even though it's not snowing and maybe some blue sky is showing, we can still get avalanches... case in point yesterday. The same could go for today so pay attention to wind features, blowing snow, wind pillows, leeward terrain off ridgetops, etc. Another soft wind slab like yesterday's observed Sun Bowl slide could certainly happen again today.
A note for all climbers and skiers heading up onto the upper mountain: Rime ice has formed on most rock outcroppings and is currently very thick. As warm days ensue, rime ice will flake off and fall down onto the slopes below. Rime ice chunks can be very large and very hard, enough to potentially kill you or cause serious injury. Beware of this hazard. Keep your eyes up slope as you climb and move laterally to avoid falling chunks of ice. If continuous ice fall is encountered turn around and descend to climb another day!
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LOCAL AREA ROAD, NORDIC, AND SNOWMOBILE PARK STATUS:
The Sand Flat cross country ski trails are in good shape and ready for your cross country skis and snow shoes. These are backcountry routes 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 have not been groomed in the past week and a half due to constant deep snow fall. 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 OPEN. The Everitt Memorial Highway is OPEN. The Castle Lake and Everitt Hwy are plowed year round to the trailheads. The roads are not always first priority, so your dawn patrol powder mission might be ceased if the plow has not made it up yet. Siskiyou County does a great job keeping the roads clear and be respectful of the plow drivers if you encounter them. If you get to Bunny Flat before or during when the plow is there, please park on the uphill, LEFT side of the parking lot as you drive in. This is uphill and lookers right of the bathrooms. Thank You!
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 30 F, 5 degrees cooler than yesterday at this time. Skies are partly cloudy with calm wind.
On Mt Shasta (South Side) in the last 24 hours...
Old Ski Bowl - 7,600 feet, the current temperature is 20 degrees F. Snow on the ground totals 164 inches with no new snow and 3 inches of settlement. Temperatures have ranged from 18 F to 30 F.
Gray Butte - 8,000 feet, the current temperature is 19 degrees F. Temperatures have ranged from 15 F to 29 F. Winds have been primarliy moderate out of the northwest, 10-20 mph with gusts to 42 mph and then became variable since 1900 last night, 3-5 mph with a gust to 14 mph, southeast.
Mt Eddy Range (West side of Interstate-5)...
Castle Lake - 5,600 feet, the current temperature is 26 degrees F. Temperatures have ranged from 23 F to 39 F. Snow on the ground totals 79 inches with no new snow and 1 inch settlement.
Mt Eddy - 6,500 feet, the current temperature is 20 degrees F. Temperatures have ranged from 17 F to 30 F. Snow on the ground measures 93 inches with no new snow and 2 inches of settlement. Winds have been southerly in nature with an average of 2-3 mph, and a maximum gust of 11 mph, ESE.
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: | 19 |
| Max. temperature in the last 24 hours: | 32 |
| Average wind direction during the last 24 hours: | Northwest until 1900, then variable |
| Average wind speed during the last 24 hours: | 15-20 mi/hr |
| Maximum wind gust in the last 24 hours: | 42 (Gray Butte) mi/hr |
| New snowfall in the last 24 hours: | 0 inches |
| Total snow depth: | 107 inches |
Two Day Mountain Weather Forecast
Produced in partnership with the Medford NWS
| For 7000 ft to 9000 ft | |||
|---|---|---|---|
|
Wednesday (4 a.m. to 10 p.m.) |
Wednesday Night (10 p.m. to 4 a.m.) |
Thursday (4 a.m. to 10 p.m.) |
|
| Weather | Partly sunny, with a high near 46. North wind 5 to 10 mph, with gusts as high as 20 mph. | Partly cloudy, with a low around 32. West northwest wind 5 to 10 mph, with gusts as high as 20 mph. | A slight chance of rain and snow showers before 11am. Mostly sunny, with a high near 49. West northwest wind 5 to 10 mph, with gusts as high as 20 mph. Chance of precipitation is 20%. |
| Temperature (°F) | 46 | 32 | 49 |
| Wind (mi/hr) | North 5-10 mph, gust to 20 mph | West/Northwest 5-10 mph, gust to 20mph | West/Northwest 5-10 mph. gust to 20 mph |
| Precipitation SWE / Snowfall (in) | / 0 | / 0 | / 0 |
| For 9000 ft to 11000 ft | |||
| Wednesday | Wednesday Night | Thursday | |
| Weather | Partly sunny, with a high near 25. Wind chill values as low as -5. Windy, with a north northwest wind 20 to 30 mph with gusts higher, decreasing in the afternoon. | Mostly cloudy, with a low around 22. Wind chill values as low as -1. Windy, with a west northwest wind 20-30 mph and gusts higher in exposed terrain. | A 20 percent chance of snow showers before 11am. Mostly sunny, with a high near 26. Wind chill values as low as zero. Windy, with a west northwest wind 30 to 40 mph, with gusts higher in exposed terrain. |
| Temperature (°F) | 25 | 22 | 26 |
| Wind (mi/hr) | North/Northwest 20-30 mph with gusts higher in exposed terrain | West/Northwest 0 | West/Northwest 30-40 mph with gusts higher in exposed terrain |
| Precipitation SWE / Snowfall (in) | / 0 | / 0 | / 0 |
