Logan Avalanche Advisory

Forecaster: Toby Weed

BOTTOM LINE

Danger by aspect and elevation on slopes approaching 35° or steeper.
(click HERE for tomorrow's danger rating)


Danger Rose Tutorial

The avalanche danger will rise with heavy snowfall and wind-drifting in the backcountry today. Expect to find a CONSIDERABLE (3) danger, with triggered wind slab and persistent slab avalanches 1 to 2 feet deep likely on slopes steeper than around 30 degrees and some naturals possible in exposed upper elevation terrain, especially during periods with rapid accumulations... Very dangerous and much bigger deep slab avalanches are possible on steep slopes still plagued by weak sugary snow near the ground... These are most possible on upper and mid elevation slopes with generally shallow snow cover.

Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential for safe backcountry travel.

CURRENT CONDITIONS

Winds picked up significantly out of the southwest yesterday evening, and they're cranking out hourly average wind speeds in the upper twenties. A moist Pacific storm is descending upon the region this morning and you'll likely find "full on" winter conditions in the mountains today. Expect periods with rapidly accumulating snow, serious wind drifting, and increasing avalanche danger..

There's now 71" of total snow on the ground at the Tony Grove Snotel containing 68% of average water for the date. Its 15 degrees at the 9700' Campbell Scientific--Logan Peak weather station and a west-southwest wind is currently averaging 25 mph.

RECENT ACTIVITY

Locally; numerous avalanches were reported across the forecast zone in the last week..By far the vast majority of these involved the newest snow picked up since a nice layer of surface hoar was covered and preserved by light snow on Wednesday 2-10-10. A few very large natural deep slab avalanches became visible with brief clearing on upper elevation west facing slopes in the Mount Naomi Wilderness. A rider triggered a good sized soft slab off Cornice ridge over the weekend. Appears he was able to stay in the saddle and ride out of the avalanche. It was close to 2 feet deep and around 120 feet wide on a north facing slope at around 9400' in elevation. A skier triggered a foot deep slab that broke just below his party on Monday on a northwest facing slope at around 8200' in upper Green Canyon....

Here's an updated local backcountry avalanche list:


THREAT #1
WHERE PROBABILITY SIZE TREND
      Over the next 24 hours.

We expect a general increase in avalanche activity today. Probably mostly shallow, stiff wind slabs this morning in our area after last night’s southwest winds due to lack of much existing fresh and movable snow, but these could well be quite sensitive. Fresh wind slabs and storm snow avalanches will become more likely this afternoon as fresh and drifted snow is deposited on slopes plagued by weak surface snow.

THREAT #2
WHERE PROBABILITY SIZE TREND
      Over the next 24 hours.

A weak layer consisting of feathery frost crystals or small sugary grains is widespread across the region. We've observed numerous triggered and natural avalanches on this persistent buried layer recently, and some of these avalanches occurred on fairly low angle slopes. In many areas, a significant slab has not yet formed. The additional load from accumulation and drifting today is likely to increase avalanche activity on this weakness, and likely avalanches might not be as manageable or forgiving anymore....

THREAT #3
WHERE PROBABILITY SIZE TREND
      Over the next 10 hours.

Weak sugary or faceted snow near the ground is notoriously slow to heal, and recent natural deep slab activity in the zone proves that a brood of dragons is still hanging around. I'm particularly concerned by huge recent natural deep slab avalanches on upper elevation east and west facing slopes in the Mount Naomi Wilderness .. Cougar Peak 2-19?-2010, South Fork of High Creek

Although the danger of deep slab avalanches is gradually diminishing, additional loading from accumulation and drifting today could reactivate the deep weakness in some areas.. Triggered deep slab avalanches could step down to weak snow near the ground and be very broad and destructive. Deep slab avalanches might be initiated from a shallower area on the slab, so watch out for steep rocky or terrain with generally shallow snow cover. You might trigger a dangerous avalanche from a distance or from below.

MOUNTAIN WEATHER

Expect stormy conditions today with storm totals of 8 to 14 inches forecast by tomorrow morning in the mountains...Areas favored by a southwest flow will do best with this... Should see a return of high pressure and fair weather later Thursday and Friday. A weak and warmer storm will affect the region over the weekend, but it looks like most of the energy will go south.

GENERAL ANNOUNCEMENTS

I will be issuing morning avalanche advisories for the Logan area on Mondays, Wednesdays, Fridays and Saturdays.

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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.

I will update this forecast Friday morning. Thanks for checking in....

This information does not apply to developed ski areas or highways where avalanche control is normally done.  This advisory is from the U.S.D.A. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.

This advisory provided by the USDA Forest Service, in partnership with:

The Friends of the Utah Avalanche Center, Utah Division of State Parks and Recreation, Utah Division of Emergency Management, Salt Lake County, Salt Lake Unified Fire Authority and the friends of the La Sal Avalanche Center. See our Sponsors Page for a complete list.