Avalanche Advisory
Advisory: Provo Area Mountains Issued by Trent Meisenheimer for Sunday - March 18, 2018 - 7:16am
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Today the avalanche danger is CONSIDERABLE. Layers of weak faceted snow is lurking in the snowpack 2-5' feet deep and can produce large avalanches. Also, with new snow and strong winds, many fresh wind slabs and storm slabs will be found. These slabs may be 1-2' feet deep and up to 100' wide. Safer conditions exist on southerly facing slopes without wind drifted snow or on terrain that is under 30° in steepness.




special announcement

Episode 7 of the UAC Podcast "Mastery and False Mastery - An Interview with 'Big' Don Sharaf" is live. With a snow career spanning 30 years, Don has learned about the profound value of humility and the idea of mastery and if such a thing can exist in the avalanche world. Available at the UAC blog, ITunes, Stitcher, or wherever you get your podcasts.
current conditions

Under a cold northwest flow we have increasing clouds and mountain temperatures remain in the low teens at upper elevations. Winds are from the northwest with speeds of 5-10 mph gusting into the teens. In the past 24 hrs we've picked up another 4-8" of new dense snow. Today will be all time riding conditions with blower powder on all aspects. Probably the best day of the season in my book. However, it also has avalanche accident written all over it.

Total water amounts since Wednesday morning:
recent activity

No observations from Provo were submitted yesterday.

In the SLC mountains: Yesterday there were two notable avalanches that broke into old snow. The first was a natural avalanche off Mt. Baldy in upper Little Cottonwood Canyon - it was 4-6' deep 100' wide running 900' down slope. The other was in upper Day's Fork when a backcountry tourer triggered a cornice on approach that then triggered an old snow avalanche that was 3.5' deep 80' wide and running down into the flats. (picture below)

Numerous storm slabs were triggered yesterday - many of these were 12'' deep and up to 100' wide, failing within the storm snow. Backcountry riders also reported that the snow was cracky and slabby, especially in the wind zone. Dry loose avalanche were also noted in terrain > 30°.

Photo: Bill Nalli - Deep slab in upper Day's Fork.

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

Storm Slab: Heavy snow fall has created instabilities within the storm snow. This issue will be on all aspects and elevations above about 8,000'. I would expect storm slab avalanches failing within the new snow to be touchy this morning, especially in steep terrain. These will be 12-18" deep and up to 100' wide and large enough to bury a person. The good news, is this problem should begin to settle out this afternoon.

Wind Slab: Strong winds over the past few days have drifted snow onto many aspects and elevations. The most suspect terrain will be north through south-east facing slopes at upper elevations. To add insult to injury - it will be hard to identify this problem, because they are now covered by yesterday's 6-12" of new snow. Always avoid rounded pillowy snow or fresh drifts of wind blown snow.

Loose Dry: Any slope steeper than 30° will produce long running sluffs within the top few inches of low density snow. Be sure to manage your terrain by heading from safe point to safe point and don't ride above your partner.

Cornices: Have grown large and sensitive in the past few days. Yesterday during my field day I was able to remotely trigger a cornice just by walking close to it. Give these a wide berth as they tend to break further back than expected. If you're walking ridges today make sure no one is below you before approaching cornices.

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

With upwards of 1.81" inches of water weight falling through-out the range you can expect these deeper weak layers to be coming back to life. The evidence is our neighnboors to the north where two old snow avalanches triggered yesterday, both failing at the ground and large enough to kill a person. Deep Slabs are not to be taken lightly, these are killers. They will be most pronounced at upper elevations facing the north half of the compass. They are easy to avoid - watch your slope angles, making sure nothing is steep above or adjacent to you. Choose conservative terrain and give your self outs if something does happen.

Here’s what we know about this avalanche problem:

  • Layers of weak faceted snow exist near the ground and just under an obvious dust layer.
  • These layers are buried 2-5 feet deep with a strong and supportable slab on top of them.
  • With continued loading since Wednesday morning, these faceted layers are stressed by the weight of new snow and more likely to fracture and produce a large avalanche.

Quick thought on water weight: Picture a football field covered in 1.81" of liquid water. If you do the math you'll see it comes out to roughly 535,000 lbs that's 267 tons or simply put -the weight of six Boeing 737 air planes. Now the scary thought is to think about tilting all that weight up to 38° degrees. How would you feel walking underneath or riding when that much weight comes crashing down?

weather

We will continue to be under a northwest flow for much of the day. You can expect increasing clouds and spotty snow showers this afternoon. Winds will be from the north and may increase as the day goes on. Speeds should be in the 10-15 mph range with the occasional gust into the 20's at upper elevations. Temperatures will remain cold only topping out into the mid 20's this afternoon. Brief high pressure for the start of the week before we turn wet and windy again by mid week. I love it when the National Weather Service forecaster tells you there is a moisture tap coming out of the tropics by mid week.

general announcements

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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 occur.