Observation: Brighton Perimeter

Observation Date:

04/25/2017

Observer Name:

Region:

Salt Lake

Location Name or Route:

Brighton: Millicent Bowl, Back Bowls

Weather

Sky:

Obscured

Precipitation:

Heavy Snowfall

Wind Direction:

Northwest

Wind Speed:

Moderate

Weather Comments:

Skies were Obscured throughout most of the morning hours with very brief periods of Broken up until 1430 upon exiting. Heavy snowfall with S3 rates up until 1130. Winds were Moderate and out of the WNW, and Wind Blown and or Transport was Moderate to Intense at times. Temperatures remained cool until 1100, and then especially when there were the brief periods of sunshine intermixed with low cloud cover the temperatures appeared to escalate.

Snow Characteristics

New Snow Depth:

18"

New Snow Density:

Medium

Snow Surface Conditions:

Powder

Wind Crust

Melt-Freeze Crust

Damp

Snow Characteristics Comments:

Excellent deep powder riding in the early to mid morning hours. New snow for the storm was at least 15 inches at 0700 Tuesday morning and then another 4 to 7 fell during the day with the brunt of this falling by 1100. As the sky lifted in the late morning hours Greenhousing was taking place and the only slopes that appeared to survive were north facing and above 9500 feet with slope angles of at least 30 degrees. Below 9000 the snow got exceedingly wet and thick. The winds scoured upper elevation ridgelines with west and northwest aspects.

Red Flags

Red Flags:

Recent Avalanches

Heavy Snowfall

Wind Loading

Cracking

Collapsing

Rapid Warming

Poor Snowpack Structure

Red Flags Comments:

Poor snowpack structure appeared to be reactive at just above the old snow/new snow interface from prior to any snow falling before mid day on Monday. There appeared to be a possible Melt Layer Recrystallization process occurring at this interface. The 4 to 6 inches of new snow that fell on Monday had a minimal melt freeze hardnening form in the upper 2 to 4 inches of this Layer, and directly below this was a much less dense and possibly faceted layer. Formal and hasty snow pack structure tests indicated very easy and clean shears at this break/layer. Widespread natural and very easy human triggered avalanche activity was observed. The entire Millicent Bowl had signs of a natural cycle that appeared to have gone around 0900 during the heavy PI and wind event. Two parties worked together to release the arm pit of the Millicent Shoulder. These slides were easy to trigger with remote triggering, slope cuts and or small peices of cornices being knocked on to the NE facing steep terrain just off the loaded area of the shoulder. Propagating cracks and avalanches ran across the slope up to 150 feet wide. Shooting cracks were observed on most aspects and steep slopes that had received even minimal wind transport and or loading. The shoulder was immediately reloading with cross loading WNW winds. Muffled collapsing was observed when even crossing the Bowl even on areas that had already slid and had debris.

Avalanche Problem #1

Type:

Wind Slab

Trend:

Decreasing Danger

Problem #1 Comments:

See avalanche report from Patsy Marley Shoulder as well as the previously cited Millicent Bowl and Shoulder areas. Wind Slabs appeared to be mostly Soft Slabs needing only 4 finger density to help create cohesive reactive slabs. The moderately warm afternoon temperatures generated by greenhousing may have helped reduce the reactivity of this widespread avalanche problem, yet in the upper elevation SE, E, and NE terrain there may be lingering issues on Wednesday. Yet as the W and SW winds begin to accelerate again prior to the next round of precipitation, the upper elevations may see another round of loading and activity.

Avalanche Problem #2

Type:

Storm Slab

Trend:

Decreasing Danger

Problem #2 Comments:

Along with the previously cited Wind Slab issues, there was a very sensitive and reactive density break that was producing Soft Slab issues within the new snow, and in many places there was widespread avalanching in reactive layers directly above the old snow/new snow interface. Both Wind Slabs and Storm Slabs appeared to align with the widespread unusually wide propagating avalanche cycle that was observed and reported by multiple parties. In upper elevation terrain above 9800 feet this issue may still show signs of reactivity on Wednesday morning.

Danger today was Considerable, and any periods of direct sunshine on Wednesday morning and or early afternoon may see this same Considerable Danger rating but more likely as a result of Wet Loose activity. Any periods of elevated wind development and or heavy PI may see another round of natural activity.

Today's Observed Danger Rating:

Considerable

Tomorrows Estimated Danger Rating:

Considerable

Snow Profile Coordinates:

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Observation: Brighton Perimeter

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