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Logan area Avalanche Advisory

Sunday December 30, 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 Sunday December 30th, 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 Import Auto.

†††††††††††† Current Conditions:

The Central Bear River Mountains picked up well over a foot of cold powder snow since yesterday morning, with the Tony Grove Snotel reporting a solid inch of snow water equivalent in the last 24 hrs. Youíll find deep snow and seriously drifted conditions in the backcountry today, and you should avoid steep slopes and avalanche paths or run-out zones.†† The National Weather Service has the Bear River and Wellsville Ranges under a Winter Storm Warning until 6:00 this evening. Expect up to 10 additional inches of accumulation and strong west northwesterly winds. Itís currently 14 degrees with a 20+ mph wind and gusts recorded in the 50+ mph range from the west northwest at the CSI weather station on Logan Peak. Iím reading 20 degrees and 14 new inches of accumulation at the Tony Grove Snotel site with 56 inches of total snow on the ground.

††††††††††† Avalanche Conditions:

Weíre getting reports of significant natural and triggered wind slab avalanches in the Central Wasatch Range and Ogden Area Mountains, and weíve picked up more snow and wind up in the north. The new and wind deposited snow is falling on a variety of young snowpacks across the region.Upper elevation slopes that had a couple feet of snow cover before the December 19th-20th storm are cursed by weak sugary or faceted snow near the ground, while south facing and lower elevation slopes that didnít have preexisting snow only have a couple week-old layers of fairly solid snow.Last week I noticed areas where the upper layer of snow was showing signs of faceting, weakened by the cold.

With all this nice light snow, we experienced lots of wind drifting yesterday at upper elevations. Cornices hanging over north and northeast facing slopes grew significantly during the day as winds deposited loads stiffened snow on the slopes below.Shifting and strengthening winds and continuing heavy snowfall will further build up cornices while forming drifts and wind slabs in lee slope avalanche starting zones today. In some areas wind slabs likely formed on weak sugary surface snow called near surface facets, and these are likely to be sensitive to your weight today. Watch for vertical cross loading around terrain features like sub-ridges, rock outcroppings, and gullies. Fresh powder may obscure recent drifts or slabs, so donít only trust your eyes. .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.

Iím still concerned by the possibility of deeper 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 deep dwelling monsters, but you might awaken one from a thin spot on the slab. Watch out for steep rocky areas and slopes with generally shallow snowcover. The weight of a few snowmobiles at one time on a slope or an overrunning smaller wind slab avalanche might also do the trick.

†††††††††††††† Bottom Line:

With heavy snowfall and intensifying winds in the forecast, the avalanche danger will continue to increase today.This morning thereís already a CONSIDERABLE avalanche danger in the backcountry.Natural avalanches are possible and dangerous human triggered avalanches are probable on upper elevation wind drifted slopes steeper than about 35 degrees. With additional significant snowfall and intensifying westerly winds, the danger is likely to rise to HIGH on steep wind drifted slopes during the day.Both natural and human triggered avalanches will be likely, and travel in avalanche terrain is not recommended.

Mountain Weather:

A cold front, packing strong WNW winds and more significant snowfall will move southward across the region today, and a high pressure system will build into the region for early part of next week.West northwest winds and snowfall are expected to increase throughout the morning and itíll be downright stormy in the mountains today.Expect up to 10 more inches of accumulation through tonight at upper elevations in the Bear River Range.A high pressure system will start to build in on Monday, and it looks like itíll be quite cold Monday night under mostly clear skies.The high will bring significantly warmer temperatures to the mountains and haze to Cache Valley for Tuesday and Wednesday.Looks like more productive weather in the late part of the week, with a moist southwesterly flow setting up over the regionÖ

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.