Nov 17, 2010 @ 12:34 pm

November 17 Conditions Update

Hello!  This is Steve Karkanen with early season avalanche information from the West Central Montana Avalanche Center in Missoula.

A robust winter storm passed through western Montana this week leaving several inches of heavy dense snow in most mountain locations.  This storm appeared to favor mountains north of Missoula with the Rattlesnake and mountains surrounding the Seeley Lake area receiving 20 inches or more while the Bitterroot Mountains received about a foot at the higher terrain.  This snow is heavy and dense with about 3.5” of snow water equivalent.

This is exactly the type of snow we like to see in the early season and bodes well for stability.  This is quite unlike last year when we started out with shallow snow that was exposed to very cold temperatures for several days giving us a very weak base layer well into January.

The primary avalanche concern now is how well new snow bonds to the older snow.  Most avalanches happen during or immediately after a storm so it is important to pay close attention to steep slopes where the snow has buried anchors such as rocks, brush and stumps.

The leeward side of higher ridges and gullies or couloirs tends to be the place where people can easily get into trouble early in the season.  Getting caught in even a small slide can have nasty consequences if you are carried into a terrain trap or dragged through rocks that are not completely buried.

This is a great time to get out for early season skiing and riding but remember if it’s deep enough to recreate on, it’s deep enough to slide.  Hunters are not immune as they can easily find themselves on avalanche terrain while chasing animals.

The major red flags or indicators of an unstable snowpack condition are:

  • Recent avalanche activity – this is the clearest indicator of an unstable snowpack that many people overlook.
  • Heavy new snowfall or rain – most avalanches happen during or immediately after a storm
  • Collapse noise or a whumpfing sound of the snow – if you experience this on flat terrain assume unstable conditions on a steeper slope.
  • Shooting cracks or fracture propagations running out from you as you travel, typically associated with collapse noise.
  • High winds – any amount of snow with wind can quickly raise the avalanche danger on leeward terrain.
  • Warming temperatures – a storm that starts out cold and turns warm puts heavy snow on cooler weaker layers.

If you see any of these indicators, the snowpack is unstable.

We plan to begin issuing avalanche advisories twice weekly on December 17 and will post information statements as needed until then.


This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.