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Observation: Brighton Perimeter

Observation Date
4/17/2019
Observer Name
B
Region
Salt Lake » Big Cottonwood Canyon » Brighton Perimeter
Location Name or Route
Alta/Brighton Periphery
Weather
Sky
Few
Wind Direction
Northwest
Wind Speed
Light
Weather Comments
Overnight lows dipped well below freezing for a number of hours with early morning temps in the teens. WNW winds were on the high end of the light range. Wind blown and or transport was moderate on and only observed on the upper ridge lines.
Snow Characteristics
New Snow Depth
5"
New Snow Density
Low
Snow Surface Conditions
Powder
Wind Crust
Melt-Freeze Crust
Damp
Snow Characteristics Comments
Cold overnight temperatures combined with the the last remnants of the latest storm left 10 to 12 cm of light density snow resting on the ambient m/f crust. This m/f crust was a result of the extremely warm temperatures observed on Sunday and Monday. Yesterdays saturated structure observed 60 cm down was able to dry out due to the snowpack being able to vent out all that residual heat. This ambient m/f crust served as an excellent bed surface for the widespread activity observed today. As well, this ambient crust provided a superb spongy carving base for excellent powder riding in the morning hours. At 1400 the only remaining cold snow turning was found on NW and N aspects with slope angles greater than 30 degrees. Below 9000 feet the residual warmth trapped in the snowpack was still evident.
By 1100 E and S aspects were getting damp, and by 1300 these same aspects were wet. All aspects with slope angles less than 35 degrees also were getting damp by early afternoon.
Red Flags
Red Flags
Recent Avalanches
Wind Loading
Rapid Warming
Poor Snowpack Structure
Red Flags Comments
Poor snowpack structure identified at the aforementioned interface of the ambient m/f crust to the cold dry snow from the last of the latest event. Widespread loose (dry and wet) avalanches were easy to trigger with any downhill vertical movement on slopes 33 degrees and greater. Significant debris piles were accumulating, and in many locations they were running far and leaving up to at least 1 meter of debris. As the day progressed on, even the northerly aspects appeared to become more reactive. As expected any aspects on the lower half of the compass were yielding widespread natural activity, and this same interface appeared to be the culprit layer of concern. (See photo below)
Avalanche Problem #1
Problem
New Snow
Trend
Decreasing Danger
Problem #1 Comments
Yesterdays reactive wind slabs appeared to settle out, yet evidence of natural activity was observed. (see photo below)
Widespread loose dry avalanching, as described above, was evident on every rider triggered descent on steep slopes. After todays extreme heat, this problem may still exist only on the steep north facing slopes above 9000 feet.
Avalanche Problem #2
Problem
Wet Snow
Trend
Increasing Danger
Problem #2 Comments
When exiting at 1400 the wet activity as described above was just beginning to peak, and most likely this issue became even more widespread and devastating in the later afternoon hours. With the forecast for increasing temperatures into near record figures over the next 72 hours, this problem most likely will become even more widespread and include all northerly facing terrain and keep moving higher in the terrain progressively by Friday.
Todays widespread natural activity may become more isolated and specific on Thursday, and as a result the danger may drop on Thursday to Moderate.
Of note, the Cornice concerns as previously indicated for weeks may also become a more serious problem of concern over the next 72 hours.
1st photo natural widespread wet loose from Wolverine Cirque
2nd photo natural wind slab from Wolverine Cirque.
Today's Observed Danger Rating
Considerable
Tomorrows Estimated Danger Rating
Moderate