Issued by Trent Meisenheimer on Sunday morning, April 8, 2018
Today the avalanche danger is CONSIDERABLE at upper elevation northwest through east facing slopes 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 and be very destructive.
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Weather and Snow
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 1.0 - 2.57" of snow water equivalent falling throughout the range. 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 Avalanches
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.
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
Wet Snow
Type
Location
Likelihood
Size
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.
Additional Information
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.
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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.
