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Avalanche Advisory for 2016-12-08 06:56:41
- EXPIRED ON December 9, 2016 @ 6:56 amPublished on December 8, 2016 @ 6:56 am
- Issued by Nick Meyers - Shasta-Trinity National Forest
Bottom Line
Steady, southerly wind and 5-7 inches of new snow overnight has created CONSIDERABLE avalanche danger near and above treeline on Mt. Shasta. Below treeline, expect overall MODERATE danger. Near and above treeline, recently formed wind and storm slabs on our old, smooth and firm snowpack will be encountered today and could be sensitive to trigger. Be extra cautious on W-NW-N-NE-E facing slopes steeper than 35 degrees.
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
The onset of our storm, still currently in progress, began yesterday afternoon at 1600 hrs. Moderate southeast, south and then southwest winds have transported snow onto leeward W-NW-N-NE-E slopes creating wind slabs near and above treeline. Triggering a new wind slab near and above treeline today is likely.
Below treeline, lack of a smooth bed surface on our old snowpack will most likely keep new snow in place. The odd steep slope could see a small human triggered wind slab, but unlikely.
It will be your duty to keep an eye out for signs of wind slab formation and sensitivity to triggering today. Cornices, human triggered cracking of the snowpack, wind pillows or travel where you quickly find yourself stepping from icy, scoured snow to fresh, new wind deposited snow are all signs that you may be on a wind slab. Wind slabs often appear stable but can "pop" without warning. Traditional stability tests are not always a great method to test wind slabs. Use obvious clues of instability like shooting cracks, recently avalanche activity and visible blowing snow.
Ridgelines, concave shaped bowls, chutes and couloirs, convexities or roll-overs, and rock outcrops are all prime terrain features that can host wind loading of new snow today. It is unknown how sensitve to trigger they will be and we have some uncertainty regarding this. Based on weather and snowpack observations, new wind slabs will continue to grow in size as steady snow and wind is forecasted. Cold, light density snow on a smooth, icy bed surface could be a recipe for an avalanche.
A little early season reminder: Always pay attention to wind direction. Remember, if we say a "south" wind, that means the wind is blowing from the south. If we say a "north" aspect, that means the slope is facing north. Thus, a south wind would transport snow onto a north facing (leeward) slope. The slope facing the wind is called "windward".
Pay attention to local orographics. Mt Shasta is known for creating funky wind eddies and backwinds. Even though the primary wind direction is southerly, wind slabs can sometimes form on the odd aspect. Cross-loading of slopes is also possible and often seen on the NW aspect of Gray Butte and the West Face.
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
Steady deposition of new, light density snow overnight followed by additional snow and warming temperatures today could create storm slab instability. Temperatures and snow levels are forecasted to rise throughout the day. Snow levels should reach upwards of 6,500 to 7,000 feet by this afternoon. With additional precip in the forecast, this warming could create the "upside down cake effect" where heavier snow falls on top of lighter density snow and coupled with a smooth bed surface. We have seen slides in the past that were seemingly absent of a weak layer and failed simply at a density layer change in the snowpack, due to a change in temperature and/or wind speed. Steeper slopes (>35 degrees) near and above treeline will be most prone to this avalanche problem. Below treeline, human trigger of a storm slab is unlilkely but not impossible somewhere in the forecast area.
Forecast Discussion
New snow overnight and a series of storms will continue to deliver steady snow, wind and potentially lower elevation rain at times over the next several days. We have been in the early winter duldrums for a while that has created a rock hard, smooth snow surface for most of the forecast area, especially near and above treeline. While we do not have any existing weak layers of concern, we DO have concern for light density snow on top of a icy smooth bed surface. It is now time for you to be very careful with your terrain choices if traveling in the backcountry. It is the age old question of uncertainty: How well will the new snow bond to the old snow surface? From the looks of it and from our best estimate, not that well. Strong winds will often sublimate light density snow right off the mountain, but winds have been moderate thus far and potentially just right for optimal wind loading of avalanche prone slopes. Winter is here, avalanches are possible and you need to make sure to have your 'A' game in place.
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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 from Bunny Flat, ascending up and along Green Butte ridge, Broadway and to the top of Green Butte proper yesterday were downright firm. I've been on Broadway, which is the above treeline broad, lower portion of Green Butte ridge before you gain GB proper, and it was the first time where one could have almost used crampons! Yes, it was that icy and firm. The general goal for yesterday was to get a look at the current snow surface condition so we knew what this new snow was falling onto. Overall, very smooth and very firm snow surface conditions were widespread near and above treeline on Mt Shasta. A few islands of wind sculpted, hard, wind packed snow was observed, but these seemed fairly sparse. Below treeline, conditions were firm albeit breakable crust in most areas. The warm temperatures we experienced last weekend created a widespread melt/freeze crust that required ninja skills to safely navigate on skis. Zero signs of instability were noted.
Since about 1600 yesterday, the westerly moving storm has brought 5-7 inches of new, light density snow to the forecast area. These totals are from the Old Ski Bowl, Castle Lake and Mt Eddy snow depth sensors. Winds began southeast in nature last night and swung more southwest early this morning, a steady 10-15 mph with gusts 25-35 mph.
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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
The westerly moving warm front is moving into Siskiyou County/Southern Oregon today. Cold air still remains trapped in areas keeping snow levels low. As the day progresses, expect warming temperatures and rising snow levels, upwards of 6,500 to 7,000 feet. Precipitation is expected to continue with about .16 inches of snow/water equivalent for the daylight hours today. We should see another several inches of snow on the mountain and west of the Interstate. South/Southwest winds are going to blow, peaking in the early afternoon. From the looks of it, a steady trickle of snow and fairly constent wind is going to be the normal for the next several days.
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In Mt Shasta City at 0500, we have a current temperature of 31 F, fourteen degrees warmer than yesterday. The skies are obscured with light snow falling.
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 46 inches with with 5-7 inches new snow since 1600 yesterday and no settlement. Temperatures have ranged from 12F to 20F.
Gray Butte - 8,000 feet, the current temperature is 19 degrees F. Temperatures have ranged from 14 F to 25 F. Winds have been blowing 10-15 mph with gusts to 35 mph, easterly in nature up until early this morning when they switched to more southerly, 10-15 mph, gust to 28 mph.
Mt Eddy Range (West side of Interstate-5)...
Castle Lake - 5,600 feet, the current temperature is 22 degrees F. Temperatures have ranged from 15 F to 27 F. Snow on the ground totals 22 inches with 7 inches of new snow since 1600 yesterday.
Mt Eddy - 6,500 feet, the current temperature is 23 degrees F. Temperatures have ranged from 9 F to 24 F. Snow on the ground measures 24 inches with 6 inches new snow since 1600 yesterday. We're seeing southerly winds averaging 2 mph, gusting to 10 mph over the last 24 hours.
THIS SEASON PRECIPITATION for MT SHASTA CITY: Since October 1st (the wet season), we have received 16.74 inches of water, normal is 8.97 inches, putting us at 186% of normal. For the month of December we received 0.27 inches of water, normal is 1.61 inches, putting us at 16% of normal, and finally... for the year of 2016 we've received 49.64 inches of water, normal is 36.97 inches, putting us at 134% 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: | 24 |
| Max. temperature in the last 24 hours: | 25 |
| Average wind direction during the last 24 hours: | Southerly |
| 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: | 5-7 inches |
| Total snow depth: | 28 inches |
Two Day Mountain Weather Forecast
Produced in partnership with the Medford NWS
| For 7000 ft to 9000 ft | |||
|---|---|---|---|
|
Thursday (4 a.m. to 10 p.m.) |
Thursday Night (10 p.m. to 4 a.m.) |
Friday (4 a.m. to 10 p.m.) |
|
| Weather | Snow before 1pm, then snow, possibly mixed with freezing rain between 1pm and 4pm, then rain and snow, possibly mixed with freezing rain after 4pm. Breezy | Rain and snow, becoming all snow after 10pm. Windy. | Snow. Breezy. |
| Temperature (°F) | 32 | 32 | 34 |
| Wind (mi/hr) | South 20-30 mph | South/Southwest 20-30 mph | South/Southwest 20-30 mph |
| Precipitation SWE / Snowfall (in) | / 3-7 | / 2-4 | / 2-4 |
| For 9000 ft to 11000 ft | |||
| Thursday | Thursday Night | Friday | |
| Weather | Snow before 1pm, then snow, possibly mixed with freezing rain. Windy | Snow. Windy. | Snow. Windy. |
| Temperature (°F) | 19 | 20 | 23 |
| Wind (mi/hr) | West/Southwest 30-40 mph, gusts 50+ | West/Southwest 3-7 | West/Southwest 30-40 mph, gusts 50+ |
| Precipitation SWE / Snowfall (in) | / 3-7 | / 4-8 | / 3-7 |
