Avalanche Advisory
Advisory: Salt Lake Area Mountains Issued by Greg Gagne for Friday - January 20, 2017 - 5:04am
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The avalanche hazard is LOW on most slopes today, with a MODERATE hazard of triggering loose sluffs on northerly aspects, particularly in steeper, upper elevation terrain. Wind drifts that formed early in the day on Thursday from moderate to strong south and southwest winds may still be sensitive in isolated terrain along upper elevation ridgelines and northerly aspects. If the sun does come out for any extended period, loose wet sluffs are possible on steeper solar aspects.




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current conditions

Temperatures range throughout the teens in the Salt Lake mountains and west/northwest winds are light, gusting to less than 10 mph.

Snowfall totals from Thursday are generally 3" in Big Cottonwood Canyon and along the Park City ridgeline, and up to 5" in upper Little Cottonwood Canyon. Despite ample available moisture, the lack of orographic lift on Thursday limited snowfall totals.

Week in Review

Not much to report. A dominant ridge of high pressure with clear skies and cold nights through late this past week and into Wednesday led to a weakening of the snow surface on many aspects, with several observations noting surface hoar crystals [photo below] as well as near-surface facets. Winds began to increase on Wednesday night and into Thursday morning, before diminishing midday on Thursday. A weak storm system deposited 3-5" in the Salt Lake mountains on Thursday.

On Wednesday, pro observer Mark White provided - as usual - an excellent observation of the snow surface prior to Thursday's small storm. Note how he highlights a thin temperature crust on west aspects that cap weaker faceted snow underneath. Observations from Thursday in the Salt Lake mountains indicated winds and warm temperatures likely* destroyed the surface hoar layer ahead of the snowfall, but the layer of near-surface facets has been preserved on many shady aspects at the mid and upper elevations underneath Thursday's storm snow. (* Read comments below regarding my suspicions.)


recent activity

There was minimal avalanche activity reported from Thursday, with observers noting surface sluffing in the new snow, especially on steeper shady aspects where this storm snow fell on a weak, pre-existing snow surface. These sluffs were running fast and far, but with minimal storm totals, were not entraining much 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

The primary avalanche concern for today is Thursday's storm snow sluffing, especially on steeper aspects in upper elevation terrain. These loose snow sluffs are likely, and although they won't involve much snow, they could take you for a ride in steeper terrain. Ski cuts are a very effective technique at mitigating this hazard.

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

In addition to sluffing in the loose storm snow, there are a few other avalanche concerns to watch for today:

  • Moderate to strong south and west winds blew overnight Wednesday into Thursday, creating pockets of shallow wind drifts along upper elevation ridges and leeward aspects. Although I could only find these small pockets in isolated areas, be sure to consider the consequences of triggering one of these wind drifts in steep, rocky terrain.
  • If the sun does come out for any extended period today, loose wet sluffs are possible on solar aspects.

We could use your help: There were few observations from Thursday, and from what we heard from the Salt Lake area mountains, the layer of surface hoar has seemingly been destroyed prior to Thursday's small storm, but the layer of faceted snow has been preserved underneath the new snow. I'm suspicious, and am expecting some surface hoar has been preserved in sheltered northerly terrain - particularly at the mid elevations - in the Salt Lake area mountains. (Indications from the Ogden area mountains are that this layer of surface hoar has been preserved underneath the storm snow.)

With more snow and wind in the forecast, these buried weak layers could become reactive with additional loading. If you are getting out, dig your hand down in the top 6 - 8" of snow and let us know if you are finding these weak layers, particularly any surface hoar. The shovel tilt test is an especially useful tool for our current scenario. As always, we appreciate any observations we receive from the field.


weather

Temperatures will rise into the low to mid 30's at 8000', and 20's at 10,000'. Winds will remain light and will begin to increase about midday from the south. By late this afternoon, upper elevations will see gusts increase to about 30 mph. Today will be mostly cloudy, with a possible break midday allowing periods of sun before it clouds up again this afternoon. Snowfall is expected overnight and enhances Saturday morning as the flow shifts to the northwest. Storm totals of 6-12" are possible with this next storm. A brief break followed by yet another storm later on Sunday that lasts into at least early the coming week.

general announcements

Remember your information can save lives. If you see anything we should know about, please help us out by submitting snow and avalanche conditions. You can also call us at 801-524-5304, email by clicking HERE, or include #utavy in your tweet or Instagram.

To get help in an emergency (to request a rescue) in the Wasatch, call 911.  Be prepared to give your GPS coordinates or the run name. Dispatchers have a copy of the Wasatch Backcountry Ski map.

Backcountry Emergencies. It outlines your step-by-step method in the event of a winter backcountry incident.

If you trigger an avalanche in the backcountry, but no one is hurt and you do not need assistance, please notify the nearest ski area dispatch to avoid a needless response by rescue teams. Thanks.

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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 exist.