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Logan area Avalanche Advisory

7:30, Saturday February 9, 2008

Hello and good morning, this is Toby Weed of the Utah Avalanche Center with your Logan Area backcountry avalanche and mountain weather advisory.  It’s Saturday February 9th, at 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 Avalanchetools.com.

Current Conditions: We were happy to find fairly good soft snow conditions in sheltered terrain yesterday. Although still a bit inverted and filled with graupel and rimed crystals, we found the snow in protected areas somewhat powder like. Trail breaking and off trail riding was still trying, but getting easier and a little more supportable. We could pick up a few flakes in the mountains today, and cloud cover should keep a lid on the warming temperatures. West winds are still cranking along the ridges, with the CSI Logan Peak weather station reporting 20+ mph hourly average wind speeds and gusts near 40 mph. Temperatures at mountain stations are up at least 10 degrees compared to yesterday’s readings, with 17 on Logan Peak and a balmy 33 degrees down in Logan…The Tony Grove Snotel reports 2/10ths of an inch of water in the last 6 hrs, now reading 101 inches of total snow.

Avalanche Conditions: Extensive drifting caused numerous natural and triggered wind slab avalanches across the mountains of Northern Utah on Thursday. Many of these in the Logan Area took place at lower elevations, (photos from 2-8). From Yesterday I have reports of a few triggered wind slab avalanches on the generally low angled back side of Beaver Mountain. These “slow moving” slabs ranged from less than a foot to 3’ deep and extended up to around 150’ wide. In tests, I found the slabs to be bonding a little better and the general snowpack considerably less unstable than on Thursday. But, in many places thick wind slabs formed on light density powder and the structure is weak. In some places I was still unable to isolate a slabby column in test pits.

Strong west winds since Wednesday drifted tons of snow into avalanche starting zones and built up huge cornices and stiff, thick wind slabs. You’ll find the most substantial wind deposits and greatest avalanche danger at mid and upper elevations, under large growing cornices, and near ridge lines. But significant drifting also occurred well off ridge tops and on exposed slopes at lower elevations where generally weaker snow exists. Also, vertical cross-loading led to substantial wind slab formation near sub-ridges, in gullies, and under cliff bands. The wind built stiff heavy drifts on much lighter powder that was previously on the surface, creating a fairly unstable situation. In most cases these new snow instabilities have already healed up, but especially thick slabs sitting on especially loose powder may well still be sensitive to triggering. In some areas locally drifts formed on slopes with buried persistent weak layers, which may result in lingering instability and future triggered avalanches.

Temperatures will rise well above freezing at lower elevations, and if the sun pokes out for a little while warming will be greatly accelerated. This will cause an elevated danger of wet avalanches. Given the quantity of snow existing at lower elevations, some wet avalanches could cause unexpected problems for people unused to avalanche danger. Steep snow covered slopes in the foothills could produce significant avalanches endangering low elevation trails and properties. Watch for avalanches descending onto the river trail or the First Dam Area for example….

Bottom Line: There’s a MODERATE danger on steep slopes in the backcountry, and you could trigger avalanches on various slopes and at all elevations. Pockets with a CONSIDERABLE danger probably exist on some upper elevation slopes steeper than about 37 degrees with significant recent deposits of wind drifted snow. These could still be hanging in a delicate balance, only needing a trigger to produce a dangerous avalanche. Warming this weekend is likely to cause a CONSIDERABLE danger of loose wet avalanches at lower elevations, especially if the sun comes out for a little while……You should continue to avoid and stay out from under steep drifted slopes at upper elevations and warming slopes down low.

Mountain Weather: Expect diminishing west winds, cloud cover, and some continuing snow showers today. A couple additional inches may accumulate during the day. It will warm up significantly over the weekend, and we’re likely to see a bit of sunshine tomorrow. Low elevation temperatures are forecast to be well above freezing today and warmer still on Sunday. A storm will affect mainly far Northern Utah on Monday, and a stronger system is expected mid-week.

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

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.

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.