Avalanche Advisory
Advisory: Logan Area Mountains Issued by Toby Weed for Thursday - December 15, 2016 - 6:12am
bottom line

Expect tricky avalanche conditions and a rising danger in the backcountry today, with the onset of a complex and potent Pacific storm. Dangerous wind slab avalanche conditions already exist at upper elevations, and heavy snowfall, rain at lower elevations, continuing strong southwest winds, and warm mountain temperatures will cause a host of other avalanche problems. The danger may rise to HIGH with the strong storm overnight, and natural avalanches may occur.

  • Yesterday's snowfall and overnight southwest wind created dangerous wind slab avalanche conditions on some upper elevation slopes, and the danger will rise and become more widespread with continuing drifting today.
  • Destructive deep slab avalanches failing near the ground are possible on some steep upper elevation north facing slopes, and you still might trigger persistent slab avalanches (failing on a mid-pack weakness) in steep terrain.
  • Warm temperatures and rain at lower elevations could cause a heightened danger of wet avalanches on steep slopes with saturated snow.
special announcement

***Discount lift tickets for Beaver Mountain, Snowbasin, Powder Mountain, and the Central Wasatch resorts are now available, donated by the resorts to benefit the Utah Avalanche Center. Details and order information here. These make a great holiday gift and all proceeds go towards paying for avalanche forecasting and education!
current conditions

There's now 3 to 4 feet of total snow above about 8000', with more on some slopes. The Tony Grove Snotel at 8400' reports a balmy 34 degrees with several inches of new snow yesterday and .8" of water. The snow at the site contains 93% of average water content for the date. The CSI Logan Peak weather station reports 26 degrees and a 30 mph south wind with gusts near 50 mph early this morning.

Beaver Mountain opens today with great snow cover. Remember you are entering the backcountry when you leave the ski area...
recent activity

There was a fairly widespread natural avalanche cycle across the zone on Saturday, during the height of the storm. Most of the evidence of this activity was blown in, covered up, and well hidden by the continuing storm Saturday night and Sunday. No triggered avalanches were reported locally.

Most evidence of the weekend natural cycle is blown in and covered up by snowfall that continued subsequently, but not this sizable crown on a steep north facing slope west of Tony Grove Lake.

We've received a couple reports of audible collapsing in the local backcountry, with an extremely large and loud whumpf reported from the Top of Garden City Bowls on Monday morning. Whumpfs are audible collapses of the snowpack, indicating areas of unstable snow.

Avalanche Problem 1
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 24 hours
description

Strong south winds yesterday evening and overnight drifted yesterday's new snow into stiffer wind slabs in exposed upper and mid elevation terrain. The drifting also built out ridgetop cornices that are likely to be sensitive to human triggering today. Continuing and intensifying southwest wind will cause a rising danger throughout the day. Dangerous wind slab avalanche conditions may develop by this afternoon on some drifted slopes at upper and mid elevations. Drifts developed and may build on weak snow on the snow surface before yesterday's snowfall. It's always a good idea to avoid stiffer recently drifted snow on steep slopes. Drifts may appear rounded and chalky and they may produce hollow, drum-like sounds. Watch for deposits of drifted snow in and around terrain features like gullies, scoops, sub-ridges, and cliff-bands.

Storm snow avalanches or soft slabs involving the new snow are possible on slopes where yesterday's snow accumulated on weak surface snow. The danger of storm slab avalanches will increase with accumulation this afternoon, overnight, and tomorrow.

Some slopes sport feathery frost crystals on the snow surface called surface hoar. This has a nasty habit of becoming a tricky persistent weak layer when buried intact...(Davis, 12-12-16)
Avalanche Problem 2
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 24 hours
description

Triggered persistent slab avalanches are still possible on some steep slopes at upper and mid elevations. The prolonged storm last weekend overloaded preexisting faceted snow, weakened rapidly last week by a large temperature gradient due to the very cold temperatures in the mountains. A strengthening persistent mid-pack weakness made up of small grained near surface facets is still apparent in test pits..

***Dangerous and destructive deep slab avalanches, failing on weak faceted snow or depth hoar near the ground are possible on upper elevation north facing slopes. Drifting and the load from significant accumulations will create a rising danger of deep slab activity.

Avalanche Problem 3
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 24 hours
description

Warming temperatures and rain at lower and mid elevations will create heightened wet avalanche potential. There is potential for significant rainfall late today and overnight below about 8000' in elevation. Best avoid to stay out from under steep slopes with sloppy saturated snow.
weather

The National Weather Service has issued a Winter Storm Warning for all the mountains of northern Utah and southeast Idaho

.A windy and wet Pacific storm and associated cold front will cross the region tonight into Saturday.

Weather Forecast: Tony Grove Lake (41.897,-111.6535), Elevation: 8800'
Today: Snow showers likely, mainly after noon. Cloudy, with a high near 36. Breezy, with a west southwest wind 21 to 28 mph, with gusts as high as 39 mph. Chance of precipitation is 70%. Total daytime snow accumulation of 1 to 3 inches possible.
Tonight: Snow showers. Steady temperature around 35. Breezy, with a southwest wind 24 to 28 mph, with gusts as high as 39 mph. Chance of precipitation is 100%. New snow accumulation of 7 to 11 inches possible.
Friday: Snow showers. Temperature falling to around 23 by 5pm. Breezy, with a west southwest wind 21 to 24 mph, with gusts as high as 34 mph. Chance of precipitation is 100%. New snow accumulation of 6 to 10 inches possible.
Friday Night: Snow showers likely, mainly before midnight. Mostly cloudy, with a low around -7. Wind chill values as low as -26. Blustery, with a northwest wind 18 to 23 mph, with gusts as high as 33 mph. Chance of precipitation is 60%. New snow accumulation of around an inch possible.

general announcements

The early season is a great time to refresh yourself and practice companion rescue techniques with your partners. Companion Rescue Practice Video

Check out Avalanche Canada's "Rescue at Cherry Bowl" story HERE

Between now and Jan 15th: Donate to the Utah Avalanche Center by shopping at Whole Foods Market Utah! When you visit any Utah Whole Foods Market locations, bring your re-usable bags, Whole Foods will donate a dime per bag to the Utah Avalanche Center - if you say DONATE my bag credit.

Remember your information can save lives. If you see anything we should know about, please help us out by submitting snow and avalanche observations. You can also call us at 801-524-5304, email by clicking HERE, or include @utavy in your Instagram. In the Logan Area you can get ahold of your local avalanche forcaster, me (Toby Weed), at 435-757-7578

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 exist.