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Avalanche Advisory for 2016-12-09 06:36:32
- EXPIRED ON December 10, 2016 @ 6:36 amPublished on December 9, 2016 @ 6:36 am
- Issued by Nick Meyers - Shasta-Trinity National Forest
Bottom Line
The avalanche danger will increase as one gains elevation today with wind slabs as our main avalanche problem. Overall, MODERATE avalanche danger exists in our forecast area. Above treeline on Mt Shasta, pockets of CONSIDERABLE danger are possible on W-NW-N-NE-E where recent, thick wind loading is observed on slopes steeper than 37 degrees. Below treeline, LOW avalanche danger prevails. Danger ratings could increase as additional snow and wind persist today.
Avalanche Problem 1: Wind Slab
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Likelihood ?CertainVery LikelyLikelyPossible
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Additional new snow and moderate to strong southwest wind will continue to build wind slabs today and tonight. Expect wind slabs to exist near and above treeline on W-NW-N-NE-E-SE aspects. Said slabs should be most suspect primarily above treeline and on the upper mountain on slopes steeper than 37 degrees. Wind slabs could be several feet thick in some areas. Our warming trend may further the problem in that these wind slabs will be more dense than the underlying snow beneath. Look for clues of wind slab development such as blowing snow, cornices, wind pillows. Terrain features like ridgelines, rock outcrops and narrow couloirs are perfect areas to collect wind transported snow. Traditional stability tests are not always the best method for testing wind slabs. Wind slabs can often pop without warning taking you with it. Best to use visual/auditory observations like recent avalanches, shooting cracks and drum-like, hollow sounding snow and simply avoid slopes with recent or active wind loading.
Forecast Discussion
The storm that brought us 5-7 inches of new, light density snow on Wednesday night quickly developed a 4-finger density rain/temperature crust yesterday. Wind transport of new snow was visible and occuring during the night and early morning hours. Once temperatures and snow levels rose, snow available for transport diminished. This is true for below and near treeline areas. Poor visibility did not allow for observation above treeline where temperatures remained cooler and the warming trend had less effect on the snowpack. Wind transport of snow likely occured for most of the day yesterday at upper elevations. We currently have an upside down layered snow pack, that is dense snow on top of lighter density snow within the top 15-20 cm of new snow.
Fairly typical for Mt Shasta, the avalanche danger will increase as one gains elevation. That said, visibility may not allow travel above treeline today anyways! Slopes above treeline, greater than 37 degrees and hosting evidence of wind slabs will be the most important avalanche problem and area to watch out for today. Don't let your guard down near treeline where even a small, unsuspecting steep slope could also host the isolated wind slab. Remember those obvious clues that mother nature gives us for free....don't ignore them! Recent avalanches, blowing snow, significant new snow, shooting cracks/whoomfing, rapid warming/rain on snow.
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LOCAL AREA ROAD, NORDIC, AND SNOWMOBILE PARK STATUS:
The Sand Flat cross country ski trails are in good shape still 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 CLOSED for the time being but will be opening soon! The trails are covered in snow and they are working on getting things going this month. http://www.mtshastanordic.org
The Pilgrim Creek & Deer Mountain Snowmobile Parks are open, however there is no snow at these locations currently. One must drive down the 19 road (Military Pass) for several miles to get to consistent snow before unloading. Private industry is logging out there so watch out for log trucks. 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 Everett Memorial Highway is OPEN. The Castle Lake and Everett 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. 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.
Recent Observations
Observations made from near treeline along Green Butte ridge yesterday trended toward wind slabs as our primary avalanche problem, less so with our storm slab problem. Instabilities were confined to within the new snow layers. HS (height of snow) 150cm and 15-20cm HN (height of new snow). Small column tests and hand shears resulted in failures with easy force (x2) and failures on isolation (x2) on a density break within the storm snow 15cm down from the snow surface. Winds from the S, SE, E, NE were observed throughout the day and snowpack loading was most obvious on westerly aspects with drifts measured 30-60cm. Freezing rain in the afternoon capped the snow surface with a 4F hard zipper crust. No avalanches, shooting cracks, or collapses were observed. Check the full pit profile (Green Butte Ridge - 12/8) in obs section below.
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Have you seen our new, BIG BLUE buttons on our website? Yep, thats them, just up and to your left! You can use those and absolutely should. No more email, no more text, no more messing around! So cool. Please submit your observations by clicking either 'snowpack' or 'avalanche' observation and follow the template. Just a photo? Great! Snowpit profile? Awesome! Video, notes, weather...you name it, there is a place for it. It's simple, easy and fun and extremely useful for us and other users. We also have a drop down menu within the obs template that allows you to submit observations from "out of the forecast area". Heading to Crater Lake or Mt Lassen? Submit some obs! This will help us create the BEST possible avalanche advisory AND provide a great place for peeps to go for checking backcountry conditions. Saddle up!
Weather and Current Conditions
Weather Summary
Snow is in the box for the foreseeable future. The warm front that brought balmy temps and high snow levels moves overhead this morning. Another system moving in today should dump its load primarily tonight with periods of heavy precipitation. About .85 inches of SWE is expected by Saturday morning. So, increasing snow showers today, the brunt of it tonight and tapering off tomorrow. Snow levels will fluctuate for the next 24 hours before colder air drops down over Northern California late Saturday. Expect snow levels at 4,700 feet today, about 6,000 feet tonight, 5,000 feet tomorrow and dropping to town by Saturday night/Sunday. Oh no, I have not forgot about our friend, The Wind. You know it.... above treeline, primarily southwest wind will start us off for the next 24 hours and gradually switch to westerly as the weekend progresses. A steady 30-40 kt blow will keep things sporty for any backcountry traveler venturing above treeline. Near and below treeline, winds will be less. The Wind will be present for most of the weekend. As for long term, a weaker storm arrives Sunday and more snow and periods of rain for next work week too.
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In Mt Shasta City at 0500, we have a current temperature of 42 F, eleven degrees warmer than yesterday.
On Mt Shasta (South Side) in the last 24 hours...
Old Ski Bowl - 7,600 feet, the current temperature is 30 degrees F. Snow on the ground totals 47 inches with with 1 inch new snow and little settlement. Temperatures have ranged from 21F to 30F.
Gray Butte - 8,000 feet, the current temperature is 29 degrees F. Temperatures have ranged from 19 F to 30 F. Winds have been blowing 15-20 mph with gusts to 42 mph, southwest.
Mt Eddy Range (West side of Interstate-5)...
Castle Lake - 5,600 feet, the current temperature is 10 degrees F. Temperatures have ranged from 23 F to 33 F. Snow on the ground totals 23 inches with 1 inch of new snow.
Mt Eddy - 6,500 feet, the current temperature is 32 degrees F. Temperatures have ranged from 26 F to 33 F. Snow on the ground measures 21 inches with a trace of new snow and 3 inches of settlement. Winds have averaged 2 mph with gusts to 16 mph, southerly in nature.
THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 16.81 inches of water, normal is 9.21 inches, putting us at 182% of normal. For the month of December we received 0.34 inches of water, normal is 1.85 inches, putting us at 18% of normal, and finally... for the year of 2016 we've received 49.71 inches of water, normal is 37.21 inches, putting us at 133% 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.
| 0600 temperature: | 33 |
| Max. temperature in the last 24 hours: | 33 |
| Average wind direction during the last 24 hours: | Southwest |
| Average wind speed during the last 24 hours: | 5-10 mi/hr |
| Maximum wind gust in the last 24 hours: | 20-30 mi/hr |
| New snowfall in the last 24 hours: | .5-1 inches |
| Total snow depth: | 28 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 before 4pm, then rain and snow showers. | Rain and snow showers, becoming all snow after 10pm. The snow could be heavy at times. Breezy | Snow before 10am, then snow showers likely, mainly between 10am and 4pm. |
| Temperature (°F) | 32 | 31 | 30 |
| Wind (mi/hr) | South/Southwest 10 mph, gusts to 20 mph | South/Southwest 10 mph, gusts to 20 mph | West 10 mph, gusts to 20 mph |
| Precipitation SWE / Snowfall (in) | / 3-7 | / 10-14 | / 2-4 |
| For 9000 ft to 11000 ft | |||
| Friday | Friday Night | Saturday | |
| Weather | Snow before 4pm, then snow showers after 4pm. Windy | Snow showers before 10pm, then snow after 10pm. The snow could be heavy at times. Windy | Snow before 10am, then snow showers likely, mainly between 10am and 4pm. The snow could be heavy at times. Windy |
| Temperature (°F) | 22 | 22 | 22 |
| Wind (mi/hr) | West/Southwest 30-40 mph | West/Southwest 5-9 | West 40-50 mph |
| Precipitation SWE / Snowfall (in) | / 5-9 | / 12-18 | / 2-4 |
