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Logan area Avalanche advisory

Tuesday March 28, 2006

Hello, this is Toby Weed of the Forest Service Utah Avalanche Center with your Logan area backcountry avalanche and mountain weather advisory.  It's Tuesday March 28th at 9:30 pm.  This advisory is brought to you in part by the Friends of the Utah Avalanche Center in Logan with help from Import Auto, located at 502W, 1400N.

(3-29-06, 7:30 am): The Utah Avalanche Center has issued an AVALANCHE WARNING for the mountains of northern, central and southwestern Utah.  Heavy snowfall, strong winds, and rain at lower elevations have caused the avalanche danger to rise to CONSIDERABLE in the backcountry around Logan.  The danger could rise to HIGH on steep wind-drifted slopes at upper elevations, especially in the southern reaches of the forecast area where significantly more snow and rain fell yesterday and overnight.

Mountain Weather:

The National Weather Service in Salt Lake City has issued a Winter Storm Warning for the mountains of northern Utah.  The warning extends through late Wednesday night and could very well be continued into Thursday.  In our area, the heaviest snowfall rates may hold off until afternoon and last through the evening hours. One to two feet of accumulation is possible above about 8000', and several inches will fall at lower elevations. Ridge-top southwest winds will sustain 20 to 40 mph averages overnight with much higher gusts and persist on Wednesday.  The winds should shift around from the west and diminish somewhat as precipitation intensifies Wednesday afternoon.

Snow and Avalanche Conditions:

 Freshly built and forming wind-drifts will be our biggest avalanche concern on Wednesday morning. As fresh powder piles up during the day, the wind will build it into sensitive drifts or slabs.  Wind slab avalanches will be most likely on slopes facing northwest through east.  The problems will not just be limited to directly loaded slopes and the highest ridge-tops.  Cross loading will be a factor elsewhere.   Sensitive drifts are forming, (and will continue to form), in and around terrain features like gullies, roll-overs, rock outcroppings, and sub-ridges.  As new snow falls during the day, it will hide wind-drifts formed overnight.   By afternoon, especially during periods of very high precipitation intensity, triggered avalanches will become more likely on steep upper and mid-elevation  slopes across the region.  Some natural avalanches might occur in places, as the snow may accumulate too quickly for some slopes to adjust to the new load.  Most avalanches will probably include only the new snow, failing on freshly formed weaknesses within itself.  In some areas, the new snow may not bond well to the old snow surface, and it's quite possible that a few avalanches might step down into older buried weak layers.  The southwest winds will directly load lots of slabby snow onto north and east facing slopes, the same places we've been finding both buried and surface weak layers. In some areas we've found well-developed frost crystals or surface hoar on the surface as well as buried and preserved under a foot or so of Sunday's snowfall.  On slopes susceptible to sun-crust formation, thin weak layers made up of sugary or faceted snow can be found on either side of crusts or sandwiched in between.   In the midst of the storm, you should avoid and stay out from underneath slopes steeper than about 35 degrees with significant deposits of rapidly deposited or wind-drifted new snow.

With strong winds, cloud-cover, and cooling temperatures, I don't think wet avalanches will be much of a concern.  But rain teamed up with warmth today, and some shallow lower elevation slopes have no more structure than cornmeal mush clear down to the ground.  I'll rest easier after a solid refreeze. As soon as the strong spring sun pops back out after the storm and warms up the fresh snow, (maybe Thursday afternoon), wet avalanches will quickly become an issue once again.

Bottom Line:

With heavy snowfall and high winds, the avalanche danger on steep slopes in the backcountry will rise to CONSIDERABLE on Wednesday.  Triggered avalanches are possible on many slopes steeper than about 35 degrees with significant deposits of wind-drifted or rapidly accumulated new snow, and natural avalanches may occur in some areas.  Wet avalanches are possible on saturated lower and mid-elevation slopes.  Today you should avoid and stay out from under steep slopes and obvious avalanche paths.

Current Conditions:

The mountain snowpack is still generally soft, dry, and winter-like and has yet to really feel the affects of the inevitable spring melt-down.  The Bear River Range boasts a well-above-average snow cover this year, with all stations over 100 percent of normal and the Tony Grove Snotel holding steadily at 150 percent of water equivalent snow.  However, the far northern extension of the Wasatch Spine, including the Wellsville Range, and the mountains south and west of Mantua, may actually be holding slightly less than average snow cover, with the Ben Lomond Peak Snotel reporting only 90 percent of average water equivalent snow.  Today, Ben Lomond picked up 1.2 inches of water in several inches of heavy snow, while Tony Grove only got 3/10ths of an inch.  The rain/snow-line is still high as I write, with 8000' temperatures hovering above freezing.  It's just under 30 degrees atop Logan Peak and an incessant south wind is consistently cranking out steady 30 mph averages.

General Information: 

If you're confused by some of our avalanche terms check out the cool new Avalanche Encyclopedia

For a list of recent avalanches in  the regional backcountry go to Avalanche List.  Snow nerds, check out the new Snow Profiles page.  Check out our Images Page for pictures of recent local avalanches.

Please send backcountry observations to [email protected] or leave a message at 755-3638, especially if you see or trigger an avalanche in the backcountry. We really want to hear from you, even if you think your observation is unimportant.    The information you provide may save lives...

 This advisory will expire on Wednesday night. I will update it on Thursday night.

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.