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Logan area Avalanche Advisory

Friday December 28, 2007

Hello and good morning, this is Toby Weed of the Utah Avalanche Center with your Logan Area backcountry avalanche and mountain weather advisory.  Itís Friday December 28th, and itís about 7:30 in the morning.  This advisory is brought to you in part by the Friends of the Utah Avalanche Center in Logan with help from Simmons Flexi-ski.

†††††††††††† Current Conditions:

The cold is keeping the snow nice on most slopes, and youíll find good riding and turning conditions in the backcountry across the region. Itís currently -3 degrees at the Campbell Scientific weather station at 9400í on Logan Peak, and a southwesterly wind picked up overnight, now averaging close to 20 mph with gusts in the 30 mph range.Iím reading 5 degrees at the Tony Grove Snotel site with 42 inches of total snow on the ground.

††††††††††† Avalanche Conditions:

Large snowmobile triggered avalanches continue to afflict the Western Uinta Range, and explosive control work at ski areas in the Central Wasatch Range continues to produce large avalanches running on weak faceted snow near the ground. Although weíve had two nice widespread natural cycles in the last week, (viewed on the 21st and 25th), no more recent avalanches were observed or reported in the Logan Area backcountry.Weíve noted lots of settlement in the new snow since the productive Christmas Eve storm. And, water vapor sublimation is creating small sugary grains in the new snow called near surface facets.Both processes are helping to increase snow stability by increasing the bond strength between slab and underlying weak layers and taking tension out of the most recently deposited slab.

Iím still concerned by the possibility of triggered persistent slab avalanches in some areas, which will be destructive and potentially deadly.Suspect weak layers are made up of snow that was on or below the snow surface in early December.The old underlying snow is faceted or sugary and weak, and instabilities caused by overloading slab layers are notoriously slow to heal.In most cases your weight probably wonít be enough to trigger one of these monsters, but you might be able to trigger one from a thin spot on the slab. The weight of a few snowmobiles at one time on a slope or an overrunning smaller avalanche might also do the trick. Watch out for steep rocky areas and slopes with shallow snowcover.Pay attention to obvious signs of instability like recent avalanches on similar slopes, collapsing or woomphing noises, cracking, or hollow sounding snow, and be willing to reassess your route.

There are a few soft and stiffer wind drifts that may still be sensitive, and increasing southwest winds today may build a few more.These should be fairly obvious and should be avoided on steep slopes.

†††††††††††††† Bottom Line:

Today thereís a MODERATE avalanche danger, and you could trigger dangerous avalanches on some steep slopes in the backcountry. Triggered avalanches are most possible on upper elevation wind drifted slopes with preexisting snow and steeper than about 37 degrees.

Mountain Weather:

A strong and somewhat moist southwesterly flow will control the weather pattern through the weekend, and a high pressure system will build early next week.Southwest winds picked up overnight and itís already snowing this morning in the Central Bear River Range. Warm advection snowfall will continue through the day today ahead of frontal passage later this evening. Expect 9 to 11 inches of accumulation in the next 24 hrs.Moist southwest flow continues on Saturday with even more snowfall forecast.Strengthening west winds will likely become a factor by Saturday evening.A vigorous frontal passage and another shot of snowfall is expected on Sunday.

General Information:

Check out photos of avalanches in the Logan Area on our images page.

Go to the Avalanche Encyclopedia if you have any questions about terms I use in the advisory

I'm very interested to know what you're seeing out there.  Please e-mail observations to me at [email protected] or leave me a message at 755-3638, especially if you see or trigger an avalanche in the backcountry. We keep all observations confidential.

This advisory will expire in 24 hours from the posting time.

The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content.  This advisory describes general avalanche conditions and local variations always occur.