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Logan area Avalanche Advisory

7:30, Monday March 17, 2008

Hello and Happy Saint Patrick’s Day, this is Toby Weed of the Utah Avalanche Center with your Logan Area backcountry avalanche and mountain weather advisory.  It’s Monday March 17th, 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 Import Auto.

Current Conditions: Northeast winds weren’t overly strong last night, at least since the Logan Peak wind sensor came back on line at midnight, but they might increase a bit while shifting around from the west today. Northerly winds whipping down through Cache Valley were certainly a factor yesterday, and drifts built in exposed terrain fronting on the valley. At the same time, it stayed fairly calm in the interior Central Bear River Mountains. You’ll find the best shallow powder conditions in sheltered and shady terrain at middle and upper elevations where several inches of accumulated newer snow is still mostly unaffected by wind and solar heating. Most reports from the weekend include fun and smooth ½-a-foot of dust-on-crust conditions, and there are many slopes across the region where you can find stable and enjoyable snow.

Its 11 degrees at 9400’ and the wind sensor at the CSI Logan Peak weather station is recording windspeeds averaging less than 10 mph from the north. Upper elevations in the Central Bear River Range picked up around a foot of new snow in the last four days, with the Tony Grove Snotel reading 93 inches total, containing 101% of average equivalent water.

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. Yesterday, reported activity was limited to relatively harmless long running dry sluffs, but with notoriously persistent small faceted or sugary grains to blame for the larger triggered slab avalanches on Friday and Saturday danger and concern still lingers. With the exception of some sizable loose wet sluffs on Saturday, no significant avalanches were reported over the weekend from the backcountry locally.

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 yesterday’s strong winds flowing from the north down Cache Valley, while the danger of older persistent slabs will be greatest on drifted slopes in exposed upper elevation terrain and on slopes with existing weak layers facing the northern third 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. I observed some fairly sizable natural loose wet avalanches over the weekend on sunny slopes involving the few inches of fresh snow. Today solar heating and potential greenhousing may cause the fresh surface snow to be saturated, and you may find even smallish wet avalanches entraining lots of mass.

Bottom Line:

The danger rose on this Saint Patrick’s Day is mostly green, and there’s a LOW danger, with avalanches unlikely on most slopes in the backcountry. There are a few exceptions and pockets with a MODERATE danger exist, with triggered wind slab or wet avalanches possible on slopes steeper than about 35 degrees. You might trigger persistent or fresh wind slab avalanches in exposed upper elevation terrain on steep slopes with significant deposits of drifted snow, and midday solar warming and potential greenhousing are likely to cause an increasing danger of wet avalanches on steep slopes with saturated surface snow.

Mountain Weather: A dirty ridge of high pressure will build into the region for the coming week, but we may be affected by a few systems passing to our north and some snow is possible. Expect a few inches tomorrow and a cold front with more on Wednesday night.

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.