Avalanche Advisory
Advisory: Salt Lake Area Mountains Issued by Trent Meisenheimer for Sunday - April 8, 2018 - 4:16am
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Today the avalanche danger is MODERATE at all mid and upper elevations for wet slab avalanches. Heavy rain up to 11,000 feet has soaked the snowpack. Water percolating through the snowpack could awaken buried layers and cause wet slab avalanches to break 3-6 feet deep.

The danger of these wet slabs should go away quickly with forecasted colder temperatures and no more water being added to the snowpack. For today, it's best to let the snowpack adjust to its load. Large glide avalanches are also possible in places like Broads Fork where the snow rest on large rock slabs.




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current conditions

Current mountain temperatures are in the upper 20's at 10,000' and mid 30's at 7500'. Northwest winds are cranking across the high peaks with 11,000' speeds of 40-50 mph gusting into the 70's. Overnight Mt. Baldy at the top of Little Cottonwood Canyon had an average hourly wind speed of 60 mph gusting to 92 mph. 10,000' wind speeds are 15-20 gusting into the 30's.

Rain totals are impressive with 0.8 - 2.0" of snow water equivalent falling throughout the range. Upper Big Cottonwood was the winner at close to 2" of water falling. Park City side ended up with just under an 1". Yes, these are rain totals - not snow. Yesterday, on my field day I noted rain all the way up to 10,400' in elevation.

The upper snowpack is fully saturated by rain. Riding and turning conditions will be at an all time low - especially with cooling temperatures throughout the day. There might be a short window of riding this morning before the snow surface is fully frozen and crusted by this afternoon. As the snow surface starts to freeze slide for life conditions will become a problem.

Video below is from my field day in BCC yesterday. Heavy rain at times.

recent activity

Yesterday, during the rain event we had a natural wet loose avalanche cycle on all aspects and elevations. These wet loose avalanches were confined to the upper 6-10" of the snowpack - entraining all the snow above the March 22'nd crust. Many of these were small in size although a few were large enough to bury a person. There was a report of a catch and carry in Hidden Canyon just outside the ski area boundary of Brighton.

Drew Hardesty and Zinna Wilson have a good video highlighting the wet loose activity from yesterday.

Our Week in Review can be found by clicking here, including coverage of a recent avalanche cycle in the Provo mountains.

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

With heavy rain soaking the snowpack you can expect water to be pooling on a variety of layers within the snowpack. I was able to get full propagation in my snowpit test yesterday (video below). Even though it took a relatively hard force to get the column to propagate (fracture) it tells me avalanches aren't fully out of the question.

Water percolating through the snowpack could awaken these layers and cause wet slab avalanches to break 3-6 feet deep mostly on NW, N and NE aspects where these faceted layers have existed for most of the season. With cooling temperatures the danger will be decreasing today and tomorrow and should quickly stabilize. However, I would continue to avoid steep terrain around the upper elevations. Lets wait and see how the snowpack reacts to this rain event.

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

If wet slab avalanches are hard to predict, glide avalanches are even harder. The good news is that they usually occur where a huge crack in the snowpack extends from the snow surface to the ground. We can see these glide cracks and avoid being underneath them. Places like Broad's Fork and Stairs Gulch in Big Cottonwood Canyon with smooth rock slabs are common places for these avalanches to occur. Below is a photo (M. White) of debris from a glide avalanche in Broads Fork that occurred after the last rain event on March 22.

weather

Under a moist northwest flow we will see on and off again snow showers for much of the day. Temperatures will rise into the mid 30's at 9,000'. Winds will remain from the west/northwest and continue blowing 15-20 mph gusting into the 30's at upper elevations. 1-3" of new snow is possible today.

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.