Observation: UFO Bowls

Observation Date
3/2/2019
Observer Name
Wilson, Hardesty
Region
Provo » Provo Canyon » North Fork Provo R. » UFO Bowls
Location Name or Route
UFO bowls
Weather
Weather Comments
Moist air, sky overcast to obscured, with light precip starting around 1:30pm. Maybe added up to 1" on the truck by 4:30? Winds variable, but picked up from the West for a short period around 2pm.
Snow Characteristics
New Snow Depth
4"
New Snow Density
Medium
Snow Surface Conditions
Powder
Snow Characteristics Comments
Several inches of new rimed particles made for good skiing: The wind and temperature crusts below were more heard than felt under the medium to high density storm snow.
Snow Profile
Aspect
Northeast
Elevation
7,800'
Slope Angle
28°
Comments
Pits:
We dug a shallow pit in a 210cm snowpack at 7800' on a northeast aspect. We wanted to see if Provo has the same low-elevation rain crust we've seen in the central Wasatch. In this location, it did not. We had variable results below a wind crust 15cm down, with ECTPV, ECTP15, and ECTN. No evidence from the rest of the tour that this layer was a true concern.
Another shallow pit on northeast at 8,580 feet had ECTN on the same layer.
Wind:
Winds calmer than expected through most of the tour, but picked up around 2pm and certainly contributed to cornice growth and loading.
Some small but sensitive soft slabs on the lee as we approached the UFO summit at 10,200'. Upper UFO bowls looked fat enough that we used a ridge-hugging sneak entrance to get into the main bowl.
Video of transport below reminds us that the Arrowhead Summit weather station doesn't do justice to NW flow.
Video
Avalanche. D3, maybe from 2/15-2/17 cycle?
Avalanche was 400' wide, 1000' vertical, 3-6' crown. 9600' on NE aspect, upper midslope in UFO bowl 3. It was previously reported by an observer who spotted it from Bobs Knob on 2/22, but this "direct" viewing gave a better sense of the size. Debris ran to the end of the flats, and knocked down trees on the way.
A quick pit on the old bed surface gave insight into what we might expect on upper elevation repeater paths...not an insignificant portion of the terrain, given the widespread and dramatic avalanching in mid February. 30 cm of recent storm snow on top of a few cm of small facets overlying the bed surface. Roughly 40cm of 1F+ depth hoar and facets with a 2cm pencil crust/bed surface with 5cm of newer weak faceted grains. Storm snow since the event is settled 30cm; ECTX on this layering but will activate with more load. Similar repeater paths in higher, more wind loaded areas may be more suspect.
Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Moderate
Coordinates