Avalanche Advisory – 3/30/2014

THIS ADVISORY HAS EXPIRED.

Issued: March 30, 2014 at 7:00 a.m.
Valid Until: 11:59 p.m. of issue date 

Good morning! This is Todd Hannan with the Flathead Avalanche Center avalanche advisory for Sunday, March 30, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Wednesday, April 2, 2014.


MOUNTAIN WEATHER

WeatherGraphicIn the past 24 hours we received between .2 -.7 inches of snow water equivalent, most of which came in early yesterday. Mild temperatures and the heavy nature of the snow caused rapid settlement and snow totals measure a modest 1-2 inches according to SNOTEL sites. Ridge top winds were 15-35 mph yesterday with gusts to 54 mph out of the southwest. Currently, remote weather stations and SNOTEL sites are reading 23 to 30 °F with winds out of the southwest at 5-15 mph. Today will see partly to mostly cloudy skies this morning clearing mid-day with temperatures from upper 20s to mid-30s. Light snow showers should resume this afternoon intensifying in the evening and winds will be 5-15 mph out of the southwest.

 


RECENT OBSERVATIONS

RecentObservationsGraphic

The rain was coming down yesterday morning while driving down the Middle Fork corridor, after motivating to leave the dry truck we traveled up Little Shields in the Lewis Range. The rain transitioned to snow at 5400 feet. On our ascent we found sensitive storm snow, particularly near the snow line that was slightly upside down, loose, wet avalanches were easy to trigger up to about 6000 feet. Winds were strong on the ridgelines, rapidly transporting the recent snow on to leeward slopes(photo). We did not observe any natural avalanche activity yesterday, but given the short amount of time the wind took to fill in ski tracks and our snow pit, it is possible that the evidence of any avalanche activity was quickly covered (photo). Though we did experience some cracking of the wind slabs while traveling along the ridge and on low angle slopes, they did not seem to be quite as reactive as what Erich encountered in the Swan Range on Friday. While approaching a wind loaded slope, he triggered a wind slab that was up to 20 inches deep and 200 feet wide (photo). A snow profile on a north aspect revealed a 4 inch wind slab on the surface that failed with easy force but did not propagate a fracture. We also found a 35 cm slab of recently wind drifted snow on top of an older snow surface that did propagate a fracture across an extend column with moderate force (profile, photo). On our descent we traveled very conservatively expecting to pass through the mid elevation band of unstable storm snow, but found that the upside layer that we traveled through on the way up had already settled and was not nearly as reactive as earlier in the day. Below 5000 feet shallow, loose, wet snow on top of a melt freeze crust was easy to trigger on steep slopes, but also easy to manage by staying above the moving snow and avoiding terrain traps.

Glide cracks are beginning to rear their ugly heads again this spring. Erich noted a couple of glide cracks on Friday in the Swan Range (photo), and Glacier National Park rangers noted a few in the park this past week.

We received no other observations within the past 48 hours from any other locations.

 

Ski track filling in minutes by wind drifted snow. Lewis Range 3/29/2014

Ski track filling in minutes by wind drifted snow. Lewis Range 3/29/2014

Shallow wind slab on the surface. ECTP on older wind slab. Lewis Range. 3/29/2014

Shallow wind slab on the surface. ECTP on older wind slab. Lewis Range. 3/29/2014

Cross loaded terrain features in the distance. From Little Shields, Lewis Range. 3/29/2014

Cross loaded terrain features in the distance. From Little Shields, Lewis Range. 3/29/2014

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 12-20 inches. Width: 200 ft. Vertical fall: 300-400 feet. 3/28/2014.

Skier triggered wind slab on a wind loaded slope in the Swan Range. Depth: 12-20 inches. Width: 200 ft. Vertical fall: 300-400 feet. 3/28/2014.

 

 

 

 

 

 

 

 

 

 

 


SNOWPACK DISCUSSION

Avalanche Problem #1

Wind SlabModerate to strong ridge top winds over the past several days created wind slabs that remain a concern today. Mild temperatures will help correct this problem faster but its best to let these slabs rest a while longer while they continue to adjust. In addition to drifting snow along the ridges yesterday, we also observed many cross loaded terrain features at mid-elevations on adjacent peaks. Continue to avoid wind loaded terrain and stick to lower angled slopes, especially when travelling in alpine areas. Large cornices exist and with warming temperatures this time of year they can become particularly sensitive. Longer days with even short periods of more intense sun can make them unstable. Give cornices a wide berth when travelling around them and avoid travel below them.


 

Avalanche Problem #2

WetAval Rain and mild temperatures yesterday made it easy to trigger shallow, loose, wet sluffs in recent snow on top of a melt-freeze crust at low to mid-elevations. Today, direct sun could increase the wet avalanche hazard on recent snow in elevations that remained cool yesterday. Wet, loose avalanches can start as small point releases, but are able to entrain recent storm snow and present a slow moving but increasing hazard particularly near terrain traps. Consider moving to a more shaded aspect if temperatures rapidly rise and sun begins to melt the snow surface.

 


Avalanche Problem #3

Deep Slab Deep slabs are still a problem given the weak snow found in shallow areas (video) as well as the rain crust from early March. Though these layers are deeply buried and difficult to trigger the possibility of an avalanche breaking on these layers still exists. The recent load placed on the snowpack combined with a human trigger in the right spot may be the tipping point for a deep slab. The best place to trigger an avalanche on these layers is shallow, rocky areas so avoid this type of terrain. While the chances of triggering a slide on these layers may be low the consequences are high. Given the uncertainty of these deep slabs, it is best to avoid slopes where these layers exist or just avoid steep slopes altogether.


BOTTOM LINE

Overall, the avalanche hazard is MODERATE. This means that human triggered avalanches are possible, particularly on steep slopes with lingering storm snow instabilities and on aspects exposed to direct sun. Wind loaded slopes steeper than 35 degrees above 6000 feet are rated as CONSIDERABLE, human triggered avalanches are likely in these areas and cautious route finding is essential.  

 

Moderate_2  

Considerable

 


Note: 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/skiing 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.

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.


DISCLAIMER

DisclaimerGraphic 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