THIS SNOWPACK SUMMARY EXPIRED ON January 22, 2015 @ 4:00 amSnowpack Summary published on January 21, 2015 @ 4:00 am
Issued by
Ben Bernall - Kootenai National Forest
Avalanche Character 1: Storm Slab
Storm Slab avalanches release naturally during snow storms and can be triggered for a few days after a storm. They often release at or below the trigger point. They exist throughout the terrain. Avoid them by waiting for the storm snow to stabilize.
The Saturday-Sunday storm event provided significant new loading to an already sensitive snowpack. This storm finished warm with rain on snow in the early hours of Sunday. Numerous natural soft slab releases triggered by rain were observed in the West Cabinet Range. Very few natural releases (soft slab debris in center) were observed in the East Cabinet Range and none were observed in the Purcell Range. The strong winds that accompanied the storm Sunday did not have any snow available to transport due to elevated temperatures.
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.
The persistent slab problem we have been monitoring above the Thanksgiving rain crust appears to be modifying. Recent stability tests of this layer failed to produce a fracture for the first time today. We are not prepared to "write off" this persistent slab issue over all of our forecasting area just yet. More site visits and tests that produce no fractures will be necessary for us to be confident that the problem is behind us.
Snowpack Discussion
Since our last regularly scheduled advisory (Friday, January 16th) we have experienced every conceivable winter weather event and its corresponding influence on our snowpack. Single digit temperatures Friday to nearly 40ºF Sunday. Heavy rates of snowfall Saturday afternoon followed by rain on snow Sunday morning. High winds on Sunday followed by mountain fog Monday and clear skies Tuesday. Through all of these events, if you were able to avoid the natural avalanche cycle, then you observed significant snowpack settlement and strengthening. Based on this and our forecast, we are expecting avalanche hazard to decrease over the next couple of days. Please continue to use your proven safe travel techniques and solid decision making in the back country.
recent observations
Today I visited Bear Basin in the East Cabinet Range. At 5500 feet elevation I found 41 inches of snowpack on a steep south aspect. The top inch of very soft snow was mostly graupel from late Sunday when the storm finished with above freezing temperatures. Below that is a 3 inch knife hard temperature crust that developed midday Sunday when temperatures pushed to the upper 30s F. Below this is a 4 finger soft layer of 5 inch depth that fell Sunday morning. From here to near the ground are a variety of pencil-knife hard layers. The basal layer to this snowpack is a loosely consolidated 4 inch layer. Extended Column Tests produced a fracture, but no propagation (ECTN5).
Weather and CURRENT CONDITIONS
weather summary
Weather in the Kootenai Region has been mostly wet and cool the past 72 hours. All SNOTEL sites showed above freezing temperatures most of Sunday and then below freezing Monday-Tuesday. SWE increases ranged from 0.1 inch at Banfield to 0.9 inch at Poorman. High winds from the west persisted all day Sunday, however very little snow was available for transport due to above freezing temperatures creating a wet surface layer. Today's weather in the East Cabinet Range was clear, breezy on the ridgetops, and 26ºF with one inch of new snow being mostly graupel. Forecasted weather is for increasing cloud cover through Thursday with below freezing temperatures. Winds will be out of the southwest at 3-6 mph with no chance of snow.
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.
