THIS SNOWPACK SUMMARY EXPIRED ON March 3, 2017 @ 10:55 pmSnowpack Summary published on March 3, 2017 @ 5:55 am
Issued by
Ben Bernall - Kootenai National Forest
Avalanche Character 1: Wind Slab
Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.
Abundant fresh snow and high mountain winds have created wind slabs on all aspects above 5,000'. These slabs will be isolated to exposed ridgelines and steep, cross-loaded gullies. This problem can be found in all of the higher mountain ranges across the Kootenai. With more snow and strong, south-westerly winds forecasted for the weekend this problem will likely continue as reactive slabs form in areas exposed to the winds. (see mtn. weather below)
BOTTOM LINE: Best travel advice would be to approach all steep slopes and gullies with caution. Be aware of changes in snow surface density as you climb into more open and exposed terrain, especially directly below ridgelines. Wind slabs will feel more dense and have a smooth, pillow-like appearance.
Avalanche Character 2: Persistent Slab
Persistent Slab avalanches can be triggered days to weeks after the last storm. They often propagate across and beyond terrain features that would otherwise confine Wind and Storm Slab avalanches. In some cases they can be triggered remotely, from low-angle terrain or adjacent slopes. Give yourself a wide safety buffer to address the uncertainty.
I am putting this problem in to cover multiple weaknesses in the snow pack of the Purcell Range (NW Peaks, Buckhorn, Flatiron). There are multiple weak layers in the Purcell snowpack that we are not seeing in the West and East Cabinets.
1. Buried Surface hoar in sheltered locations is producing very weak and clean shears 12" below the snow surface.
2. The snow from the last two weeks has bonded poorly to the February 16th rain event. (approximately 24" below snow surface)
BOTTOM LINE: Best travel advice for those riding in the Buckhorn/Purcell country would be to avoid all steep terrain over 30 degrees. The feed back you may get from testing and riding slopes will be inconsistent and misleading. The buried surface hoar is lurking in openings that are likely sheltered from wind and sun, it will catch you off gaurd in locations you may normally see as safe. They buried rain crust is bonded poorly to the new snow and is stubborn in stability tests; but, it will likely propagate far and deep if triggered. This layer is my primary concern as it is likely to produce a big avalanche.
Snowpack Discussion
There is some great riding and skiing to be had out there this weekend. The base is firm and the new snow is deep; however, now is not the time to push your luck in the steep terrain of the Purcell Mountains. If you are heading into the NW Peaks or Buckhorn country this weekend please use caution and make sure your friends understand the potential hazards.
recent observations
On March 2nd we traveled into the Pete Creek drainage near Hawkins Lake and performed stability tests on northeast and southeast aspect around 6,000' in elevation. Our previous few observations have been in the East/West Cabinets where new snow has been deeper and stronger than that of the Purcell mountains. In the Cabinet Ranges the primary concerns are wind loading and slab development in the higher terrain. The Purcells have a very dangerous and mixed bag of weaknesses such as the buried surface hoar and poorly bonded ice crust mentioned above in the "Persistent Slab" problem. The other issue with the Purcell snowpack is the facets and depth hoar that formed at the ground level earlier this winter when the snow was cold and thin. It is still there and will likely stay there all winter. It is unlikely that a rider/skier would trigger this weakness but the potential is there if one were to find a very thin, rocky spot. This deep weak layer may become a concern as we move into spring and the warm days begin to weaken the upper snowpack enough to trigger a deeper weakness, again its something to keep an eye on.
Pit test showing buried surface hoar layer that failed on 3rd tap from the wrist. Clean and snappy!!
Failure on rain crust. 2' deep at 6,000' on NE aspect.
Check out the Panhandle forecast by clicking the link below:
http://www.idahopanhandleavalanche.org/selkirks-cabinets/advisory#null
Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
400 AM MST Fri Mar 3 2017
DISCUSSION: Scattered snow showers this morning in northwest
Montana will diminish by mid moring. A few snow showers are
possible along the Canadian border this afternoon. Another weather
system will impact the mountains across northwest and west central
Montana starting early Saturday moring. The associated cold front
will slowly move through the region late Saturday into Sunday.
Expect widespread snow showers during this time as the front
pushes through. Expect scattered snow showers to persist through
much of next week. By the middle of next week it looks like snow
levels will rise a bit as warmer air develops over the region.
Kootenai:
--------------------------- 5000-7000 FT ----------------------------
Today Tonight Sat
Cloud Cover 95% 95% 80%
Hi/Lo Temps 33 to 38 22 to 28 30 to 35
Winds(mph) SW 19G37 SW 19G37 SW 16G31
Precip Chc 80 100 60
Precip Type sno/shr sno/shr sno/shr
Snow Amt(in) 1-2 4-6 1-2
Snow Level 3000 3500 2500
Disclaimer
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 midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.
