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Logan area Avalanche Advisory

7:30, Wednesday March 19, 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 Wednesday March 19th, at 7:30 in the morning. Today’s advisory is brought to you in part by the Friends of the Utah Avalanche Center in Logan with help from Avalanchetools.com.

Current Conditions: Looks like a warm and windy day, with clouds moving in again this afternoon ahead of a strong Pacific cold front that will bring more snow to the mountains tonight. Somewhat strong west winds whipped across upper elevation ridge-lines overnight, undoubtedly blowing and drifting the fresh snow in exposed terrain. Beaver Mountain picked up around 6 inches since yesterday morning and the Tony Grove Snotel reports 6/10ths of an inch of water in the new snow. The best powder conditions can be found at mid and upper elevations on slopes facing the northern quadrant of the compass, with moist snow, sun-crusts, and dust-on-crust elsewhere. Its 21 degrees at 9400’ and the wind sensor at the CSI Logan Peak weather station is currently recording windspeeds averaging around 20 mph from the west. West winds were averaging almost 30 mph for several hours overnight with gusts well into the 40s.

Avalanche Conditions:

It was an active weekend in the Utah backcountry with several sizable triggered and natural avalanches reported, including a few with people taking unexpected and potentially dangerous rides. Notoriously persistent small faceted or sugary grains and crust sandwiches are to blame for the larger triggered slab avalanches which continued on Monday and concern still lingers. (Wasatch photos)

Freshly formed wind slab avalanches are the main issue locally, and I noticed a couple on east facing slopes near ridge-lines in the Central Wellsville Range yesterday, (photo).

Triggered wind slab avalanches are possible on steep upper elevation slopes with significant deposits of older or recently drifted snow. Fresh drifts and wind slabs are most likely on slopes exposed to drifting from overnight strong westerly winds, while the danger of older persistent slabs will be greatest on slopes with existing weak layers facing the north and eastern half of the compass. Many avalanche slide paths in the area are well filled-in and smooth, so even relatively small avalanches might run far or fast.

I’ve been quite impressed lately by the powerful heating produced by even short windows of higher angle sunshine between clouds. Today southwest winds will bring in tropical warmth and solar heating and potential greenhousing may cause the surface snow on some steep slopes to become saturated. When the snow on a steep slope gets slushy you could trigger wet avalanches. You may find even smallish wet avalanches entraining lots of mass.

Bottom Line:

Overall, there’s a MODERATE danger in the backcountry, with triggered persistent or fresh wind slab avalanches possible on slopes steeper than about 35 degrees. Avalanches are most likely and there are pockets with a CONSIDERABLE danger in exposed upper elevation terrain on steep slopes with significant deposits of recently drifted snow. Midday solar warming enhanced by warm southwest winds and potential greenhousing is likely to cause a MODERATE danger of wet avalanches on some steep slopes with saturated snow.

Mountain Weather: The National Weather Service in SLC has issued a Winter Storm Watch for the mountains of Northern Utah for this evening through Thursday morning, as a strong Pacific cold front could bring substantial snowfall and strong winds to upper elevations. Expect southwest winds and warm temperatures in advance today. Winds will intensify and shift around from the west this evening and snow will definitely fly in the mountains, with dropping temperatures and rain/snow line after frontal passage. Continued productive zonal pattern will continue through the week and another vigorous storm is shaping up for early next week.

General Announcements:

Check out the images page for photos of some of this season’s avalanches.

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.