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Avalanche Advisory for 2015-12-25 05:55:41
- EXPIRED ON December 26, 2015 @ 5:55 amPublished on December 25, 2015 @ 5:55 am
- Issued by Nick Meyers - Shasta-Trinity National Forest
Bottom Line
MERRY CHRISTMAS TO ALL!
LOW avalanche danger will exist on all aspects below treeline for today.
MODERATE avalanche danger will exist on N-NE-E-SE-S facing slopes for wind slabs near and above treeline. Human triggered wind slab avalanches are possible today.
Avalanche Problem 1: Wind Slab
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High West/Northwest winds that blew across the area over the week have created wind slabs near and above treeline on N-NE-E-SE-S aspects. Ridge tops are scoured down to firm/frozen snow. Below ridge top's, not typically wind slab starting zones, could host the best wind slab formations due to high wind speeds. It should be noted that local orographics can create unusual wind eddies that can load other aspects. Use visual clues such as blowing snow, cornice formation, rounded and hollow sounding firm slabs, and cracking along ridge lines and extreme terrain to determine where wind slabs might exist. Wind slabs are often limited by terrain and usually have well defined boundaries. Cornices may have formed in isolated areas along ridge tops pointing toward the leeward side. Travel along the windward side of the ridge and steer clear of the ridge top. A common place to find cornices is along Casaval Ridge, the north ridge of Grey Butte or the ridge above Heart Lake/Castle Lake.
Forecast Discussion
A fresh dusting of new snow and mostly clear skies for Christmas! What a wonderful gift. Expect lingering snow showers this morning and otherwise clearing skies. Cool temperatures will continue for the immediate future. A brief warming will occur on Saturday though cool back off late Sunday. The Northwesterlies will be blowing on the mountain for the next 24-48 hours, 20-30 mph with gusts to 40-50+ mph. The next best chance at more snow will be Sunday afternoon/evening.
THIS SEASON PRECIPITATION: Since October 1st (the wet season), we have recieved 9.34 inches of water, normal is 13.41 inches, putting us at 69% of normal. For the month of December, we have received 7.31 inches of water, normal is 6.05 inches, putting us at 120% of normal. For the year of 2015 we've received 26.52 inches of water, normal is 41.41 inches, putting us at 64% of normal
Recent Observations
A few inches of new snow in the last 24 hours and continued northwesterly winds will keep things much the same as yesterday with low to moderate avalanche danger and wind slabs leading the charge for the avalanche problem of the day. Small to medium size wind slab avalanches will be possible to trigger today. Wind slabs are notoriously unpredictable, so tread lightly if you are on or near a wind slab. East and southeast aspects near and above treeline, below ridgelines on mid to upper sections of slopes will be the best places to find said wind slabs.
Castle Lake skiing is part of our picture now... it's been years! Snowpack observations made at Castle Lake showed a variety of conditions depending on aspect. The southerly, more sun exposed aspect of Right Peak hosted a thick melt-freeze crust that was supportable 75% of the time. When you did break through, it made for challenging skiing. On more northerly, shaded aspects the snow was still soft. Castle Lake is frozen over and the ice covering the lake was MOSTLY trustworthy. There are AREAS OF THIN ICE so take caution. A snow study pit was dug just below the saddle between Right Peak and the "Chutes" area below Middle Peak. Snow measured 110 cm deep on a NE aspect on a 25 degree slope. No obvious weaknesses were found amongst the layers and the PWL found elsewhere was non existent. An extended column test was performed multiple times with the same results, ECTX. There was evidence of recent avalalanche activity off of the rock buttress above Castle Lake in the form of loose dry snow point release avalanches in two locations (see photo below). The snowpack in the Castle Lake area is still in early season condition with manzanita and some rocks still poking out. You can ski and ride up at Castle Lk. but be careful for shallow hidden objects.
Wind slabs are still an avalanche problem, specifically on Mt Shasta. A naturally triggered wind slab avalanche was reported in Sun Bowl. Evidence was observed Wednesday the 23rd. Wind slabs that were formed during our most recent storm on S-SE-E-NE-N aspects and may have grown due to continued high winds through Wednesday. Avoid travel over or under areas of possible wind slab formation, known avalnche paths, and run out zones. Ridge tops remain scoured down to firm/frozen snow. Small to medium size cornices may have formed on some ridge tops near treeline and may be easy to trigger. If traveling along a ridge where cornices have formed give them plenty of room. There is a slight chance that a cornice fall my trigger a wind slab avalanche on slopes underneath on leeward aspects. Easterly aspects have shown the best wind loading. Wind slabs are guaranteed above treeline, so over snow travel will call for careful route planning.
We've been keeping close tabs of the persistent weak layer problem. Stability tests performed in areas where the layer exists are indicating a strengthening of the layer in the snowpack as warmer temps and some sun shine have helped heal the PWL. We are putting the persistent weak layer problem to bed and don't believe it will be or become a further problem.
Below: Yellow Butte pit from Mt Shasta, 12.24.15
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Below: Castle Lake pit, 12.23.15
Rock buttress above Castle Lake with natural loose dry point release avalanche just right of center of photo. Note avalanche debris from 2nd slide in bowl at lower left corner of photo - Photo: J Dove
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The Sand Flat cross country ski trails are snow covered and ready for your cross country skis or snow shoes. These are backcountry trails 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. Thank you, and Enjoy!
The Pilgrim Creek Snowmobile Park is open! Trails are being groomed currently. Head to our "Education" tab on our website and find the snowmobile section for trail information, grooming status and other sledder resources!
The Five Red Flags of Avalanche Danger any time of year include: 1) Recent/current avalanche activity 2) Whumpfing 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 24 F and partly cloudy and a light dusting of snow.
MOUNTAIN WEATHER STATION INFORMATION (0500hrs):
On Mt Shasta (South Side) in the last 24 hours...
Old Ski Bowl - 7,600 feet, the current temperature is 12 degrees F. Snow on the ground totals 63 inches with 5-6 inches of new snow in the last 24 hours with 1-2 inches settlement. Temperatures have ranged from 12 F to 17 F.
Grey Butte - 8,000 feet, the current temperature is 11 degrees F. Temperatures have ranged from 11 F to 16 F in the last 24 hours. Winds have been averaging 17 mph, northwesterly, with a max gust to 35 mph, NW.
Mt Eddy Range (West side of Interstate-5)...
Castle Lake - 5,600 feet, the current temperature is 16 degrees F. Temperatures have ranged from 16 F to 28 F in the last 24 hours. Snow on the ground measures 33 inches with 2-4 inches new snow and 1-2 inches settlement.
Mt Eddy - 6,500 feet, the current temperature is 15 degrees F. Temperatures have ranged from 15 F to 23 F. Snow on the ground measures about 52 inches with 2 inches of new snow in the last 24 hours and 1-2 inches settlement. Winds have averaged 2 mph, with a max gust to 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: | 16 |
| Max. temperature in the last 24 hours: | 20 |
| Average wind direction during the last 24 hours: | Northwest |
| Average wind speed during the last 24 hours: | 17 mi/hr |
| Maximum wind gust in the last 24 hours: | 35 mi/hr |
| New snowfall in the last 24 hours: | 4-6 inches |
| Total snow depth: | 63 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 | 30% chance of snow showers, mainly before 10am, otherwise partly sunny | Mostly clear | Sunny |
| Temperature (°F) | 21 | 11 | 31 |
| Wind (mi/hr) | North/northwest 5-10 mph | Northeast 10-15 mph with gusts to 20 mph | East 10-15 mph |
| Precipitation SWE / Snowfall (in) | / 0-.5 | / 0 | / 0 |
| For 9000 ft to 11000 ft | |||
| Friday | Friday Night | Saturday | |
| Weather | 30% chance of snow showers, mainly before 10am | Mostly clear, temps rising | Sunny |
| Temperature (°F) | 2 | 2 | 28 |
| Wind (mi/hr) | North 15-25 mph, G-30 | Northeast 0-.5 | North/Northeast 35-45 mph, G-60+ |
| Precipitation SWE / Snowfall (in) | / 0-.5 | / 0 | / 0 |
