Avalanche Advisory
Advisory: Skyline Area Mountains Issued by Brett Kobernik for Sunday - March 8, 2015 - 8:32am
bottom line

Dangerous avalanche conditions exist in the upper elevation more northerly terrain where large avalanches are likely to be triggered by people. Avoid the higher more northerly facing terrain. Some east facing slopes are suspect as well. Wet avalanche activity may also happen today with the sun heating the new snow on the sunny aspects. Get off of steep slopes as they become wet and don't linger below steep slopes or in gullies.
special announcement

Updated to include all of the avalanches that were reported over the last week including two new snowmobile triggered avalanches in Rolfson on Saturday:

Date Region Place Trigger Depth Width Aspect Elevation Weakness
03/7/2015 Skyline Rolfson Snowmobiler 2.5' 100 Northeast 10200 Facets Details
03/7/2015 Skyline Rolfson Snowmobiler 2.5' 200 Northeast 10200 Facets Details
03/4/2015 Skyline Skyline Summit Snowmobiler 3' 150 Northeast 10000 New Snow/Old Snow Interface Details
03/4/2015 Skyline Spring City Canyon Skier 2.5' 250 Northeast 10300 Facets Details
03/3/2015 Skyline Pleasant Creek Snowmobiler 20" 80 North 9200 Facets Details
03/3/2015 Skyline Seeley Creek Natural 2.5' 400 North 10800 Facets Details
03/3/2015 Skyline Jordan Canyon Natural 2' 300 Northeast 10600 Facets Details
03/3/2015 Skyline Blue Slide Fork Natural 2' 50 North 10200 Facets Details
03/3/2015 Skyline Electric Lake Natural 2' 50 Northeast 8700 New Snow/Old Snow Interface Details
03/2/2015 Skyline Spring City Canyon Natural 14" 350 Northeast 10300 Facets Details
current conditions

The new snow from early in the week is settling and travel is becoming easier but dangerous avalanche conditions exist especially on the northerly facing slopes. You'll find heat crusts on the sunny slopes this morning with good powder still on the more northerly terrain. This powder is going to act as a lure into dangerous avalanche terrain. Temperatures are in the upper 20s to low 30s with clear skies and light northwest wind.
recent activity

Two snowmobile triggered avalanches were reported from Rolfson Canyon on Saturday up to 3' deep! Photos: Cade Beck
Avalanche Problem 1
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 24 hours
description

By far, the most dangerous situation is in the upper elevation northerly facing terrain where old weak snow is now capped off with 2 to 3 feet of new snow. Human triggered avalanches will be likely through this weekend in the higher terrain. Slopes that avalanched in December are especially suspect as they have a VERY shallow and weak snowpack. This is a dangerous situation because people can travel on a lot of different slopes without triggering anything or seeing any obvious signs of instability. This may give people a false sense of security and then decide to get onto more northerly facing terrain. Make no mistake that this a bad deal. We continued to experience numerous large collapses on Friday which is a tell-tale sign that the underlying weak layer is still active.

Here's a great video which describes how the persistent weak layer of "sugary" faceted snow works:

Persistent Slab Avalanches from Trent Meisenheimer on Vimeo.
Avalanche Problem 2
type aspect/elevation characteristics
LIKELIHOOD
LIKELY
UNLIKELY
SIZE
LARGE
SMALL
TREND
INCREASING DANGER
SAME
DECREASING DANGER
over the next 24 hours
description

Wet avalanche activity is a bit hard to predict just when it will start to happen naturally. Since the new snow has gone through a couple of melt freeze cycles over the last few days during the gradual warm up, this makes me think things won't get out of hand today. However, there is a lot of new snow and if it becomes unstable the wet avalanches could pack a punch. Just be aware that things could heat up enough today to become dangerous. Continue to re-evaluate the snow conditions watching for very wet snow on sunny slopes. Stay out of steep gullies especially those that have big steep slopes above them.
weather

High temperatures today should be slightly cooler than Saturday but we'll still see ridgetop highs in the mid 30s. We'll have mostly clear skies and light northwest wind. Monday looks similar then slightly warmer Tuesday and warmer yet Wednesday. We'll see a minor disturbance move through Wednesday into Thursday with slight chance for snow then the ridge moves back in and temperatures warm again into the weekend.
general announcements

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The information in this advisory is from the US Forest Service which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.

This advisory will be updated by 7:00 AM Saturday, March 7, 2015 or sooner if conditions warrant.