Issued: Sat, Dec 30, 2017 at 7AM

Expires: Sun, Dec 31, 2017

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Above 3,500ft Moderate

2,500 to 3,500ft Moderate

Below 2,500ft Low

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

BOTTOM LINE

Buried persistent weak layers will be stubborn, but possible, to human trigger today, and difficult to predict. This is a low probability/high consequence avalanche problem.

moderate avalanche hazard exists on all aspects at mid to upper elevation today. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Natural avalanches are unlikely, human triggered avalanches are possible. Small avalanches in specific areas; or large avalanches in isolated areas.

A low hazard exists on all aspects at low elevation. Generally safe avalanche conditions. Low hazard does not mean no hazard. Natural and human triggered avalanches unlikely. Small avalanches in isolated areas or extreme terrain. Watch for unstable snow on isolated terrain features.

 


PERSISTENT SLAB AVALANCHE PROBLEM

Buried, persistent weak layers in the mid pack are 1-3 feet deep, and possible to human trigger on slopes 35º and steeper.

The distribution is widespread on all aspects at mid to upper elevations, and low continuity will keep the avalanche size to D1-2. However, this avalanche problem is more prevalent on common features of specific terrain, generally North to West, with previous wind loading and cross loading, where avalanches will be closer to D2 in size. Pay close attention to any unsuspecting gully or depression that has been cross-loaded (See example picture of Bullion Mt in recent activity below.)

Avalanches will be stubborn to trigger, often allowing multiple riders on slope before finding the weakest, thinnest trigger point in the slab.  Avalanches may be triggered from below or remotely. This makes predicting where and when an avalanche will occur difficult, and adds uncertainty.

Stiffer, more cohesive snow overlying weaker snow is the recipe. This problem can feel “drummy” or hollow, and can sometimes be identified with pole tests and instability tests. In some locations the weak layer is thinner, making it more difficult to identify with pole tests (such as in picture below). In these cases you will need to dig. If you have a highly calibrated eye, you may also be able to identify specific, loaded, problem areas by their appearance. See pictures under recent activity.

Use good travel protocol, ride one at a time, avoid slopes with terrain traps. All members of your party should wear avalanche transceivers, and carry shovels and probes. Consider using radios to tighten up communication when you become spread out from partners.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The snowpack depth is highly variable, 8 inches to 4 feet, due to wind scouring and loading over the last couple of weeks.

Gold Chord, ESE, 3950′, PST 45/100, showing propagation potential in Persistent Weak Layers in the mid-pack

 

Please view and contribute to the community observation platform HERE!

Pit profile here

Recent Avalanche Activity

MANY THANKS TO ALL WHO HAVE CONTRIBUTED OBSERVATIONS THIS SEASON!

Many human triggered avalanches were reported this week. View recent observations here

An example of cross-loaded features from previous winds on Bullion Mountain. All the depressions and gullies are loaded.

SE aspects with cross-loaded gully features. Small but deep avalanche (D1). Occurred Dec 24ish. Pockets like these will still produce results today.

 

 

 

 

 

 

 

 

 

 

Dec 26 – Marmot Mt, SW aspect, 4k’. We call this “pocket” the Catcher’s Mitt. It’s leeward to most winds due to the ridge’s position. Play with this one enough and you will likely get caught. Small slab avalanche in the shady pocket with traversing track through the top of the crown. Notice the less loaded areas did not produce avalanche results after countless rider’s descents.

 

 

 

 

 

 

 

 

 

 

 

 

Dec 22 or 23 remotely triggered avalanche. An example of the current low probability/high consequence avalanche problem. See more details from this avalanche in April Bowl under observations.

 

 

 

 

 

 

 

 

 

 

 

Human triggered avalanche Dec 24 above Stairstep

 

 

 

 

 

 

 

 

 

 

Wind pillows and loading on Marmot’s South ridge.

 

 

 

 

 

 

 

 

 

 

Widespread Surface Hoar up to 5.0 mm. Keep tabs on the surface hoar distribution and size. SH is a particularly troublesome weak layer once buried.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Recent Weather

This week’s weather at 3550′:

Temps averaged 21ºF, with a low of 7ºF and a high of 32ºF.

No new snow was recorded at IM snotel this week.

Overnight at 3550′:

Temperature averaged 18° F.

0″ new snow overnight.

This week’s weather at 4500′:

Temps averaged 16ºF, with a low of 6ºF and a high of 28ºF.

Winds averaged SE 3 mph, max SE 13 mph . Gusts averaged SE 7, max gusts SE 25 mph.

Overnight at 4500′:

Temps averaged  14ºF overnight.

Winds averaged SE 8 mph overnight, with a max gust of  16 mph.


NWS recreational forecast for Hatcher Pass here


NWS point forecast here


State Parks snow report here

Additional Info & Media

Expect the avalanche hazard to remain the same throughout the weekend.

 

Posted in HPAC Forecasts.
Jed Workman

Forecaster: Jed Workman