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Fri., Feb. 24, 2012, 8:21 a.m.

Avalanche advisory: tricky conditions in backcountry

WINTER SPORTS -- Persisting weak layers, new snow, wind, changing temperatues -- and more new snow forecast for the weekend -- add up to warnings for backcountry travelers to use great caution in the backcountry this week, according to this morning's avalanche advisory from the Idaho Panhandle Avalanche Center.

"Tricky conditions in the mountains today due to weak layers of facets below a crust and buried surface hoar," says Kevin Davis, the center's technichian who was out checking the North Idaho snowpack on Thursday.

"Avalanches triggered in these weak layers have the potential to be larger due to firmer windslabs in the upper pack on wind scoured slopes.  A Winter Storm Warning will be in effect this evening and continuing into Sunday morning.  The avalanche hazard will rise to HIGH due to the expected weather."

Read on for the full avalanche advisory for the region. 









EFFECTIVE DATE:  02/24/2012

DATE ISSUED:     02/24/2012  0730

OUTLOOK:  02/25-26/2012

This report does not apply to local ski areas within the forecast region and the hazard rating will remain valid through midnight February 24th, 2012.  Special thanks to Idaho Parks and recreation for sponsoring this Avalanche advisory.   

Winter Storm Warningfor our forecast region from 10PM Friday to 4AM Sunday.  The National Weather Service expects 9-13 inches to fall in this period, winds to be gusty out of the west, and valley accumulations could add up also.


TODAY:  80% chance of 1-3 inches of snow to the north and minor accumulation to the south.  Temperatures in the upper 20s to lower 30s, and winds S/SW steady 10mph range and 20mph gusts.

TONIGHT:  Winter Storm Warning in effect -100% chance of 3-7 inches region wide, temperatures in the low 20s, and S winds 10-15mph with gusts in the 20mph range.

SATURDAY:  100% chance of continued snowfall with 3-7 inches to the south and 2-4 inches to the north.  Temperatures will rise to the mid to low 20s during the day and fall to the high teens at night.  Winds out of the W/SW will remain steady through the night Saturday and snowfall is expected to continue into Sunday.  Wind-loading will be significant on lee aspects.  The avalanche danger will become HIGH for the outlook period.

Selkirk and Cabinet mountains:New snow was deep from storms this week, especially last Saturdays dump.  Saw natural avalanches on easterly aspects at about 5,500’.  These were running on a layer of weak facets below a thin rain crust.  You’ll find this weak layer buried about 6-10 inches deep and shearing clean with moderate force on S and W aspects.  Two layers of surface hoar 3 inches apart now linger on all aspects about 2 feet deep on N and E aspects, 1.5 feet deep on W aspects, and on a crust about 1 foot deep on S aspects.  We may have formed another last night.  Bottom line is that all aspects have weak layers, cold temperatures are keeping them weak, and new snow and winds will stress these weak layers.  Avalanche danger is rated CONSIDERABLEon all aspects steeper than 35 degrees above 5,000 feet.  Avalanche Danger is rated as MODERATE on all aspects less than 35 degrees above 5,000 feet.

St. Regis Basin and Silver valley:  The rain crust from early this week is a consistent weak layer in the Lookout Pass area and to the south on Landmark Peak where Ed found the facets under the crust shearing easily.  This crust also popped out easy in a pit at Silver Mountain but it was not buried under as much new snow.  Watch for surface hoar formed on this crust from last night.  Dan found buried surface hoar near Mullan Pass and still shearing with moderate force on N aspects.  Weak layer distribution seems to be rain crust facets on S and W aspects and buried surface hoar on N and E aspects. Avalanche danger is rated CONSIDERABLE on all aspects steeper than 35 degrees above 5,000 feet.  Avalanche Danger is rated as MODERATE on all aspects less than 35 degrees above 5,000 feet. Watch the steeper terrain in your travels today.  There are multiple weak layers on all aspects and triggering the upper faceted layer could step down to the buried surface hoar layers.  On westerly and most exposed aspects the surface snow is firm and wind scoured and this slab could propagate into larger sized avalanches.  The upper 2 feet of snow is lighter on N and E aspects and this means it’s still possible to affect the deeper buried weak layers there.  Cold temps will allow them to persist and potentially weaken.  New snow and strong winds will stress weak layers on all aspects this weekend so be aware of the avalanche danger rising to High by Saturday. 

The next avalanche advisory will be issued March 2nd

Contact:  Kevin Davis (208) 265-6686, Ed Odegaard (208) 245-6209, or John Olson (208) 265-6635

This message is available by calling (208) 765-7323 or toll-free at 1-866-489-8664.

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Rich Landers
Rich Landers joined The Spokesman-Review in 1977. He is the Outdoors editor for the Sports Department writing and photographing stories about hiking, hunting, fishing, boating, conservation, nature and wildlife and related topics.

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