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Avalanche advisory: storm could prompt changes

WINTER SPORTS -- New snow this week has created good sliding conditions for skiers and snowmobiles. But The Idaho Panhandle Avalanche Center's weekly advisory cites conditions and areas of concern in the snowpack.

"The southerly aspects were a little firmer with suncrusts and shallower snow but the north aspects had a sufficient amount of new snow and the buried crusts were a little deeper," writes IPAC technician Kevin Davis, reporting to today on his Thursday outing to test the backcountry slopes.  "So was the buried surface hoar.  You can't miss it on the north aspects where its standing proud.  It wasn't shearing easily yesterday but check it today on steep slopes.  Your main concern this weekend will be the new snow, Winter Storm Watch, loading buried surface hoar."

Read on for the complete report.








EFFECTIVE DATE:  02/17/2012

DATE ISSUED:     02/17/2012  0730

OUTLOOK:  02/18-19/2012

This report does not apply to local ski areas within the forecast region and the hazard rating will remain valid through midnight February 17th, 2012.  Special thanks to Idaho Parks and recreation for sponsoring this Avalanche advisory.   

Winter Storm Watch for our forecast region beginning this evening and continuing into Saturday evening.  Winds will pick up with storm passage and snowfall may continue into Sunday.  We have a Dorito-sized buried surface hoar layer on north aspects, be aware.


TODAY:  Partly sunny across North Idaho today with temperatures in the mid to high 30s, light S winds.

TONIGHT:  100% chance of snow with 3-5 inches to the north and 1-3 inches to the south.  Temperatures overnight in the mid to high 20s and steady S winds.

SATURDAY:  Here’s where it gets good… 100% chance of 2-4 more inches of snow through the day Saturday, temperatures in the low to mid 20s, and winds increasing out of the S/SW with gusts to 30mph.  By Saturday evening expect a couple more inches and storm total accumulation in the 6-9 inch range.  Snowfall is expected to continue to the south and taper off to the north.  New snow will be loading a prevalent layer of buried surface hoar.  The avalanche danger will increase for the outlook period.

Selkirk and Cabinet mountains:Up around Flattop Mountain in the Selkirk’s Eric and I found a highly variable snowpack with regards to aspect and elevation but the surface snow was mostly cold and light.  Settlement has been the rule this week, although crust layers are still brittle but not breaking.  Buried surface hoar exists on all aspects but is standing at attention on north aspects.  Watch this layer on all aspects but particularly on northerly aspects where you’ll see it buried deeper from wind-loading about 6-10 inches deep.  On easterly aspects we found it on a crust and under a suncrust in the upper 6 inches.  This hoar layer could be triggered where wind-loaded today but the big concern is for more loading on this weak layer Saturday.  Avalanche danger is rated MODERATE on aspects steeper than 35 degrees above 5,000 feet.  Avalanche danger is rated as low on slopes less than 35 degrees.St. Regis Basin and Silver valley:  In the Lookout Pass area Carole is seeing a stabilizing snowpack also and her stability tests confirm this.  Crust layers are prevalent but shears are not easy.  On Marks Butte, east of Clarkia, Joel Kopf reported a mostly stable pack on a NW aspect close to 6000 feet.  Ed was up Breezy Point on N aspects and noted some weak facets around upper crusts but showing good bonding due to settlement.  Carole and Ed both mentioned the surface hoar on north aspects buried a couple inches deep.  Where wind-loaded this will be under greater stress.  Watch this to be a problem with the new snow expected on Saturday.  Avalanche danger is rated MODERATE on aspects steeper than 35 degrees above 5,000 feet.  Avalanche danger is rated as low on slopes less than 35 degrees.Today will be mostly great snow with a couple new inches of cold snow to freshen things up.  Take some time to check the distribution of buried surface hoar.  Wind-loading and new snow will be the issue this weekend as the prevalent surface hoar layer is stressed by additional loading.  You can identify this layer easily by digging down and looking for a darker layer in the pack.  Isolate a column and see if it shears easily.  Where the slab on this weak layer is firmer and deeper from wind it will be more of a problem.  Temperatures will be on the cold side so sheltered areas may not load the surface hoar enough to stress it.  Don’t just rely on what you see from one place.

The next avalanche advisory will be issued February 24th

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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