Avalanche Advisory – 2/9/2014

THIS ADVISORY HAS EXPIRED

Issued: February 9, 2014, 7:00 a.m.
Expires: 11:59 p.m. of issue date

Good morning! This is Erich Peitzsch with the Flathead Avalanche Center avalanche advisory for Sunday, February 9, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Wednesday, February 12, 2014.


MOUNTAIN WEATHER

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It seems as if we may finally be coming out of the deep freeze. As of 4:00 a.m. this morning remote weather stations are reading -13 to 6 °F with winds out of the northeast at 15-35 mph with gusts to 45 mph in the Middle Fork. (SNOTEL and remote weather stations). The cold air mass should slowly exit the region today bringing temps up to the low 20s F. Moderate northeast wind this morning will shift to the southwest this afternoon at 5-10 mph. Another disturbance south of our area gradually moves north with most of the precipitation falling south of our advisory area again. However, we may see a couple of inches of snow with the focus in the Swan Range. A pattern change that includes new snow for our area appears to be on the horizon early this upcoming week. 


RECENT OBSERVATIONS

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Yesterday, we skied into the Canyon and Skookoleel Creek drainages in the southern Whitefish Range . We found mostly unconsolidated surface snow, but still found weak snow (facets) about a foot below the surface (snow profile). These facets sit above a crust on sunny aspects. This layer was not reactive in our stability tests, and I was lulled into thinking we did not have a wind slab problem in the Whitefish Range. However, at about 6000 feet on a convex rollover on a south-southwest aspect I was able to trigger a small wind slab pocket (photo and video). It was only 30 feet wide, 10 inches deep, and did not run very far, but it reminded me that wind slabs still exist even in somewhat protected areas, and they could be large enough to knock you around or bury you.

We also found wind slabs in the Swan Range on Thursday. Underneath these hard wind slabs we found a layer of weak snow about a foot (30 cm) from the surface and another about 2 – 2.5 feet (70cm) from the surface (snow profiles and photo). Our stability tests in multiple pits on different aspects showed that a fracture has the potential to propagate on these layers (video). We also experienced a whumpf of the snowpack while traveling along the ridge indicating the layer beneath the wind slab had collapsed.

In the Flathead Range on Friday, we observed a decent amount of loose snow activity. We noted isolated wind slabs near ridge tops and in cross loaded areas at mid elevations as well.

Forest Service snowmobile rangers found facets about a foot from the surface in China Basin in the northern Whitefish Range yesterday as well. They noted the snow above this layer was unconsolidated and lacked slab qualities.

Localized cracking is isolated wind slab areas in the southern Whitefish Range. 2/8/2014.

Localized cracking is isolated wind slab areas in the southern Whitefish Range. 2/8/2014.

Debris pile from small wind slab pocket triggered in a south-southwest aspect in Canyon Creek. 2/14/2014.

Debris pile from small wind slab pocket triggered in a south-southwest aspect in Canyon Creek. 2/8/2014.

Thin layer of weak snow (facets) sitting underneath a hard slab on easterly aspect in Swan Range. 2/6/2014.

Thin layer of weak snow (facets) sitting underneath a hard slab on easterly aspect in Swan Range. 2/6/2014.

 

 


 

 SNOWPACK DISCUSSION

Avalanche Problem #1

Wind Slab

Recent winds from the east and northeast over the past few days created hard wind slabs in localized areas (video). Winds from this direction have wind loaded slopes that we may not be used to as being typical wind loaded slopes. Signs of hard wind slab include hollow sounds as you travel over them and impenetrable snow surface. Weak snow sits underneath these hard slabs waiting for the right trigger. Fortunately, these wind slabs are not widespread right now, but when you encounter them they are sensitive to human triggering. It is important to carefully identify wind loaded or wind affected slopes. I was looking for instability yesterday and could find no major signs until nearly the end of the day in the right spot. So, don’t allow mostly stable conditions to lull you into a sense of complacency.

 


Avalanche Problem #2

Loose Dry

Loose snow avalanches may appear harmless, but the ones we observed Friday were actually gouging out the surface snow up to a foot deep and 40 feet wide. They entrained enough snow to certainly knock you around and potentially bury you in a terrain trap. The surface snow seems like it really wants to become a slab, but doesn’t quite have enough cohesion yet. These loose snow avalanches still demand respect particularly in high consequence terrain or near terrain traps.

 


Avalanche Problem #3

Persistent Slab

A layer of weak snow (facets) sits underneath these hard slabs up to about 2.5 feet down. This layer propagated a fracture with moderate to hard force in our stability tests, but this clearly shows that the potential for deep avalanches exists. This hard slab appears to exist in open areas at upper elevations, but given the potential high consequence nature of persistent slabs it is important to dig and assess each slope before riding or skiing it. Hard slabs can be tricky to asses and often surprise those that trigger one. They can break above you and propagate farther than soft slabs. It’s best to avoid slopes with a hard slab.

  


 BOTTOM LINE

Generally, the hazard is MODERATE with pockets of CONSIDERABLE on wind loaded slopes steeper than 35 degrees. This means that it is likely you will trigger an avalanche on steep wind loaded terrain if you encounter wind slabs. Wind slabs are not widespread, but exist at mid to upper elevations and are sensitive to human triggering. It also still remains possible to trigger an avalanche due mostly to weak layers (facets) within the top 2 – 2.5 feet of the snowpack. Careful evaluation of where these wind slabs exists is important. 

Considerable Moderate

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Note: We received no other field observations since last Tuesday. We really need your help, folks. The accuracy of the avalanche advisory becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help. 

  


See recent snow profiles as well as snow profiles from the entire season here

Clicking on the avalanche problem icons provides a general definition for each specific problem.

Check our blog for a discussion about avalanche hazard ratings here.

New!!! Join us Feb. 12, 6:30 p.m. at Penco. We are working with the Flathead Snowmobile Association for the first in a series of motorized specific backcountry safety seminars. Details here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


Observations are extremely valuable to us. If you’ve been out in the backcountry, please drop us a line with your observations at fac.admin@flatheadavalanche.org or call 406.261.9873. Thanks!


DISCLAIMER

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This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.