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Observation: Brighton Perimeter

Observation Date
4/15/2015
Region
Salt Lake » Big Cottonwood Canyon » Brighton Perimeter
Location Name or Route
Brighton Perimeter: Claytons Peak, Green Slope and Pioneer V-Tree
Weather
Sky
Obscured
Precipitation
Moderate Snowfall
Wind Direction
Northwest
Wind Speed
Moderate
Weather Comments
Moderate Snowfall throughout the day at a consistent 1/2 inch per hour. WNW Winds were sustained in the Moderate Range with Strong Gusts. Variable Easterly (and possible wrap around winds) on the Wasatch County side of the Range. Wind Blown and or Transport was in the high end of the Moderate Range with ample amounts of light density snow available for Transport. Upper elevation Temperatures remained in the in the teens and it felt like mid-winter out there.
Snow Characteristics
New Snow Depth
21"
New Snow Density
Low
Snow Surface Conditions
Powder
Wind Crust
Snow Characteristics Comments

At 8:00 am in Silverfork at 8000 feet there was 17 inches of new snow that would be considered on the heavy end of the Light Density Category. During the day, it snowed at least another 4 inches at 8000. In the upper reaches of BCC Storm totals at 8:00 were 14 inches and it appeared to snow at least another 4 to 6 inches during the day. Densities were Lighter than lower in the Canyon. There was definitely at least 20 inches of new snow by 3:00 pm in upper BCC.

Riding conditions were also mid-winter like; and the Light density snow didn't keep you off the old M/F crust on E, S and W aspects with slope angles 30 degrees and greater. Northerly aspects, and slopes with angles less than 30 degrees rode very well with deep "right side up snow". The new snow appeared to have very few density breaks and was mostly stable in areas where the wind was not a factor.

Red Flags
Red Flags
Heavy Snowfall
Wind Loading
Red Flags Comments
Cold temperatures and very little sunshine allowed all aspects and elevations to hold cold snow throughout the day. Heavy PI rates appeared to help initiate isolated Natural Avalanches overnight and into the early morning hours. Steep upper elevation/loaded - East and Southeast aspects appeared to have Wind Aided/Storm Slabs that released and mostly refilled by 9:00. Sustained winds with optimal loading speeds were observed and also noted on various upper elevation remote weather sites. Residual (pre-storm) warmth within the snowpack appeared to help create a good bond of the old snow surface to the new snow.
Avalanche Problem #1
Problem
Persistent Weak Layer
Trend
Same
Problem #1 Comments

Wind Slabs are suspect in Isolated areas on upper elevation, steep E and SE aspects. The Wind Slabs observed were all Soft Slabs with Hand Hardness of only 4 finger. Of Note: in areas where observing Wind Slabs they appeared to be associated with sensitive cornices that were easy to release.

If the forecasted "Wrap-Around Winds" verify, then this Wind Slab Problem may be widespread on Thursday. And it may also be found on the South and West and aspects.

Slabs may be up to 3 to 4 feet deep.

Avalanche Problem #2
Problem
New Snow
Trend
Decreasing Danger
Problem #2 Comments

In areas receiving up to 2 feet and greater of Storm Totals, there may be a Storm Slab Problem, especially early in the morning on Thursday. These Storm Slabs may settle out quickly on Thursday as is expected in these Spring events. As noted before, there appeared to be very few reactive density breaks in the new snow in areas traveled on Wednesday.

Of Note: Temperatures are forecasted to be at least 20 degrees warmer on Thursday; and the skies are forecasted to be Mostly Cloudy. Yet, if there are any periods of direct sunshine that persist for more than 15 minutes on Thursday, Wet Avalanches of the Loose and Slab variety may become an issue. The Light Density New Snow that is everywhere may be able to become reactive, and there are very hard pre-storm bed surfaces on East, South and West aspects, and any possible slides may run farther and faster than anticipated. Natural Wet Avalanches should be expected.

Therefore the Trend for Storm Slab Avalanches should be Decreasing. And, the Trend for Wet Avalanches should be Increasing.

Hazard observed on Wednesday was Moderate, and with the possibility of Wet Avalanches on Thursday, the Hazard may reach into the Considerable Rating area.

Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Considerable