Avalanche Advisory
Advisory: Logan Area Mountains Issued by Toby Weed for Saturday - December 19, 2015 - 7:10am
bottom line

CONSIDERABLE (level 3): Dangerous avalanche conditions exist on drifted slopes at upper elevations in the backcountry, and in some areas you could trigger potentially large and destructive avalanches. Careful snowpack evaluation, cautious routefinding and conservative decision-making will be essential today. Avoid travel on or below drifted upper elevation slopes steeper than about 30 degrees.




avalanche watch

THE FOREST SERVICE UTAH AVALANCHE CENTER IN SALT LAKE CITY HAS ISSUED A BACKCOUNTRY AVALANCHE WATCH.

* TIMING...SUNDAY INTO SUNDAY NIGHT...THEN TRANSITIONING TO AN AVALANCHE WARNING BY LATER MONDAY.

* AFFECTED AREA...ALL THE MOUNTAINS OF NORTHERN UTAH AND SOUTHEASTERN IDAHO, TO INCLUDE THE BEAR RIVER RANGE, THE WESTERN UINTAS AND THE MANTI-SKYLINE PLATEAU.

* AVALANCHE DANGER...EXPECTED HEAVY SNOW AND STRONG WIND WILL PUSH THE DANGER TO HIGH AND PERHAPS EXTREME OVER THE NEXT SEVERAL DAYS.

* IMPACTS...BY LATER MONDAY INTO TUESDAY, LARGE AND DANGEROUS NATURAL AND HUMAN TRIGGERED AVALANCHES WILL BE LIKELY.

AVOID BEING IN STEEP TERRAIN OR BENEATH AVALANCHE RUNOUT ZONES. BACKCOUNTRY TRAVELERS SHOULD CONSULT WWW.UTAHAVALANCHECENTER.ORG OR CALL 1-888-999-4019 FOR MORE DETAILED INFORMATION.

THIS WATCH DOES NOT APPLY TO SKI AREAS WHERE AVALANCHE HAZARD REDUCTION MEASURES ARE PERFORMED.
current conditions

The Tony Grove Snotel at 8400' reports 29 degrees this morning and 35 inches of total snow containing 68% of average water content for the date. Southwest winds increased last night, easily drifting the light surface snow, with the CSI Logan Peak weather station recording sustained average wind speeds around 40 mph, and a gust of 56 mph early this morning. I'm reading 24 degrees at 9700'.

There is a Considerable danger at upper elevations and careful snowpack evaluation, cautious routefinding and conservative decision-making will be essential for safe backcountry travel. Many avalanche paths in the Logan Zone may be hanging in a delicate balance. Although significant natural activity has yet to occur, a stiffer slab layer is forming on top of widespread very weak faceted snow and in some upper elevation areas, steep drifted slopes are likely close to the tipping point. Dangerous avalanche conditions exist, especially in wind exposed upper elevation terrain, but nice, bottomless (or baseless) powder riding conditions can be found on lower angled slopes, down lower in elevation, and in sheltered areas.

Very weak faceted snow is widespread at mid and upper elevations in the Bear River Range, and it's now capped by a rather inconsistent rime or rain-crust and a foot to a foot-and-a-half of settled powder. Wind and more accumulating snow are in the process of creating a heavier slab layer on top of the loose faceted snow.

Loose faceted snow crystals plague the shallow snowpack in the Logan Zone. (12-15-2015)
recent activity

There was significant natural and remote triggered activity in the Wasatch Range Backcountry above Park City on Thursday... And a significant natural cycle in the Northern Uintas........ Go to our observations page for more details..

One of several remote triggered avalanches from Thursday in the backcountry above Park City. (Staples, 12-17-15)

Yesterday afternoon (12-18-15), I thought I could see evidence from a distance of fresh natural activity in the State Line Bowl Area north of Beaver Mountain. (still unconfirmed) A sledder reported triggering a small loose avalanche in the Gibson Basin Area north of the State Line in Franklin Basin on Thursday (12-17-15) No other avalanche activity has been reported in the Logan backcountry recently, but please report anything you may see this weekend.
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

***Pay close attention to signs of unstable snow like whumpfing and shooting cracks, and be willing to reevaluate your plans. In these conditions you might trigger avalanches remotely, from a distance or worse, from below!

Yesterday I triggered a couple fairly large audible collapses or "whumpfs" in drifted terrain in the Garden City Bowls Area. These heart-stopping noises are caused by a buried weak layer failing compressively, and they definately indicate the pressence of unstable snow conditions. Very weak faceted snow is widespread across the zone at mid and upper elevations. Last night's increase in southwest wind and significant recent local accumulations of easily drifted light snow might just be enough to overload the very weak basal snow on some slopes. Dangerous triggered persistent slab avalanches are likely in some areas, especially in drifted terrain at upper elevations.

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

Southwest winds picked up significantly overnight and there was lots of nice light powder on the snow surface, so substantial drifting probably occurred and will be ongoing today in upper elevation terrain. Wind slab avalanches may become more sensitive to human triggering as the slabs continue to build, and they may step down into weak basal snow near the ground or pull out a persistent slab in descent. Continue to avoid travel in steep drifted terrain today.

weather

It'll be mostly sunny and mild in the mountains today, with 8500' high temperatures around 37 degrees and moderate south southwest winds. It'll snow tonight, with 2 to 4 inches of accumulation forecast, low temperatures just under 20 degrees, and moderate west winds. Snow will continue tomorrow, with 1 to 3 inches possible. Significantly more snow is expected tomorrow night and Monday, with 6 to 12 inches by Monday evening, and then the storm moves in! Looks like an active, very moist and windy weather pattern will set up for next week, with significant heavy accumulations contributing to significant and rising avalanche danger in the backcountry.

Here is yesterday's Mountain Weather Briefing video from Brian of the NWS in SLC....

general announcements

Please submit snow and avalanche observations from your ventures in the backcountry HERE. You can call us at 801-524-5304 or email HERE, or include #utavy in your Instagram or Tweet us @UAClogan. To report avalanche activity in the Logan Area or to contact the local avalanche forecaster call me, Toby, at 435-757-7578. 

I'll update this advisory throughout the season on Monday, Wednesday, Friday, and Saturday mornings by about 7:30

This advisory is produced by the U.S.D.A. Forest Service, which is solely responsible for its content. It describes only general avalanche conditions and local variations always exist.