Observation: Brighton Perimeter

Observation Date
12/22/2017
Observer Name
B

Region:

Location Name or Route
Brighton Perimeter
Weather
Sky
Broken
Wind Direction
West
Weather Comments
Temperatures moderated today from yesterdays frigid lows. Afternoon temps got into the mid to upper 20's at 8700 feet. Winds appeared to surpass the forecast velocities, and even mid elevation terrain had sporadic gusts into the upper 20 mph range. Wind blown and or transport was observed from 8700 feet and higher. Clear skies in the am gave way to overcast by the end of the day. Very light snow began falling around 1730 with little to no accumlation
Snow Characteristics
Snow Surface Conditions
Powder
Wind Crust
Snow Characteristics Comments

In most mid elevation terrain, the winds had not adversely affected the surface snow conditions with the latest events light density snow providing soft turning on low angle terrain. 

Red Flags
Red Flags
Wind Loading
Poor Snowpack Structure
Red Flags Comments
Poor snowpack structure throughout the snowpack continues to the obvious red flag waiting for a new and substantial load to tip the scales and become reactive. Of note the facets above and below the Thanksgiving crust appears to be the layers of concern. Snow pit tests yielded moderate scores with Q2 shear characteristics, and there was also an SC in one other test, and this occurred in the facets below the aforementioned crust; and this crust was 28 cm down. The potential for propagation at this layer with a signficant new load appears possible.
Avalanche Problem #1
Type
Wind Slab
Trend
Increasing Danger
Problem #1 Comments

Considering the information from many remote weather stations on upper elevation ridgelines, the probability for sensitive and reactive wind slabs appeared to be likely. And, with the forecast for "breezy and gusty winds" in the next 12 hour period, this problem may even become more widespread. 

Avalanche Problem #2
Type
Persistent Slab
Trend
Increasing Danger
Problem #2 Comments

Additional loading from the incoming event may be enough to initiate failures in the buried NSF below Wednesdays light density snowfall. Of note, the previously cited layers of concern above and below the Thanksgiving crust are of primary concern. And with the forecast predicting denser/heavier snow to be falling throughout the day on Saturday these buried persistant weak layers will most likely become reactive in many locations, if the forecast verifies. 

Also of concern today, was how easy it was to initiate loose snow dry avalanches on steep northerly facing terrain, and this reactive light density snow from the latest event may also serve as an excellent weak layer interface when and if the new snow forecast for Friday night and Saturday verifies. Soft slab avalanches of 30 cm to 45 cm appear very possible, and any significant slide occuring during weekend may continue to step down into older/deeper buried weak layer. 

These multiple probabilities validate the complicated situation we may be dealing with on Saturday and beyond, as accumlating snow and wind contribute to the potential for persistent slab activity. 

In areas traveled today at the mid elevations, the danger appeared to be Low, yet with the obvous strong winds throughout the day the danger most likely was moderate, and this danger rating appears to be appropriate for Satuday with the possibility for natural avalanches if the winds and new snowfall combine a forecast levels. If this case occurs Considerable in wind loaded and new snow areas may be possible. 

 

 

Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Moderate
Snow Profile Coordinates