Wind slabs and persistent slabs on Schuylkill Ridge

CB Avalanche Center2016-17 Observations

Location: Paradise Divide Area
Date of Observation: 02/07/2017
Name: Zach Guy
Subject: Wind slabs and persistent slabs on Schuylkill Ridge
Aspect: North East, East, South East, South
Elevation: 9,000- 11,100 ft.

Avalanches: Ski cut a small windslab on a crossloaded SE slope NTL. It was about 8-12″ deep, and ran on the melt-freeze crust interface, small in size. SS-ASc-R1-D1-I. See photos.
Weather: Surprisingly calm winds, but evidence of previous wind transport from the SW at ridgeline. S-1 to S1, snow in the morning and graupel in the afternoon. About 5 cm accumulated from 12 p.m. to 4 pm. Overcast skies and relatively warm temperatures.
Snowpack: Storm total below treeline was 25 cm by the end of the day. No signs of storm slab instabilities below treeline on sunny or shady aspects, but as we approached treeline, slabs became denser and more wind affected, with drifts up to 35cm thick. Minor cracking on NE aspects, where the storm snow was on hard wind board, and moderate cracking on SE aspects, where the storm snow was on a stack of melt-freeze crusts (Feb 4 crust was 3-6 cm thick, pencil hard, and Feb 6 crust was 2 cm thick and 4F to 1F hard, with a soft layer between). On a NE aspect BTL, one pit produced moderate, propagating results, 53 cm deep on the 1/19 surface hoar, below a 4F+ slab. (ECTP16, SC). No signs of instability observed on this layer.

Skier triggered wind slab.  SE aspect NTL
Skier triggered wind slab.  SE aspect NTL
Cracking snow near treeline
ECTP16, SC on 1/19 SH, below a 53 cm, 4F+ slab.  NE aspect BTL.

A letter of protest to surface hoar

CB Avalanche CenterAvi Blog, Avi-Off-Season

Dear Surface Hoar,
First you bedazzled us with your shimmering feathers, glistening under the cloud layers that brought our unusual surface hoar event back in mid-January.  You are fragile and don’t belong in Colorado’s windy and sunny environment.   We thought to ourselves, “You’re a long shot, surely you won’t survive.”  But somehow you did.  Things started to go downhill on January 19th, when you got buried beneath a storm that came without wind, against the odds.
Unusual cloud layers and unusually widespread surface hoar layer in mid January.  Photo courtesy of MSF Films

Then more snow came, and it formed a soft slab above you, and your behavior started getting erratic through the last week of January.  We saw lots of natural avalanches, we saw avalanches breaking in dense aspen groves and on low angle slopes, and we saw slides remotely triggered from flat terrain. 

Video demonstrating the touchy and unusual avalanche behavior in late January.
It has been 2 weeks since the last storm, and we have heard about slides triggered on you almost every single day, either in our zone or our neighboring Aspen zone. There were a number of close calls and partial burials on the Aspen side. 
A slide on Mt. Emmons that caught a skier off guard.
 Things have started to quiet down this past week, and travelers are starting to let their guard down.  But with more snow on the way this week, we can’t trust you and your unruly and dangerous behavior.  It will become more sporadic and less predictable.

Video explaining our current snowpack structure on northerly/easterly aspects
I can’t recall the last time we had someone like you as widespread and troublesome in our snowpack.  Granted, a lot of things have changed in the past few weeks for the better, and we are thankful for that.  A lot of slopes have flushed.  Winds have blasted you and their overlying slabs away in places.  The sun has capped the snowpack with a stout crust on other slopes.  So now you are lurking on fewer slopes, but now the slabs above you will be growing thicker and more dangerous, and you will become more volatile again as more snow and wind prod at you.  We will see skiers and snowmobilers recreate on a lot of slopes with no apparent sign of problems from you, and our focus will be on freshly formed but manageable storm instabilities. But then somewhere you will react harshly as you buckle under increasing pressure, or someone pokes your small feathers on the wrong slope, and it will be bad news for everyone involved.  We know where you are most likely to be bothered, and that happens to be our favorite riding areas, northerly and easterly aspects near and below treeline. But we can’t know for sure where or when you will strike next.  That scares us. 
Most of the persistent slab avalanche activity in late January was on surface hoar.
Read this observation for some caveats to this diagram. 
 At the CBAC, we ask that you resign from causing problems in our snowpack, and move back to Canada, where you belong. 

Sincerely,
Zach Guy
Director of CBAC

Mountain Weather 2/7/2017

CB Avalanche CenterWeather

Date: 02/07/2017

Today will be an interesting day to watch play out as a very strong jet stream (140kt) just to our south inches farther north, creating windy conditions near and above treeline, and spurring heavier snowfall. Previous models suggested lower elevations to be fighting the snow/rain line down valley, but that does not look as likely anymore. However, expect heavier, dense snow falling especially near and below treeline. Tonight, snow and winds will peak, before tapering off Wednesday afternoon. Storm accumulations look on track with 1-2 feet possible by Wednesday afternoon. Thursday dry and sunny, before another storm takes aim for Friday and Saturday.

Today

High Temperature: 28
Wind Speed: 20-30 G50
Wind Direction: SW
Sky Cover: Mostly Cloudy
Snow: 4-8″

Tonight

Low Temperature: 24
Wind Speed: 20-30 G60
Wind Direction: SW
Sky Cover: Mostly Cloudy
Snow: 4-8″

Tomorrow

High Temperature: 24
Wind Speed: 10-20
Wind Direction: W
Sky Cover: Mostly Cloudy
Snow: 2-4″

Buried surface hoar- Coney’s

CB Avalanche Center2016-17 Observations

Location: Crested Butte Area
Date of Observation: 02/06/2017
Name: K and K Rohrig
Subject: Buried surface hoar- Coney’s
Aspect: North East
Elevation: 10,800′

Avalanches:
Weather: Obscured, sporadic snow with periods of intense snow
Light S winds
Snowpack: Top of Convex Corner on Coney’s, just below the ridge line, < 30 degrees
250 cm HS
5-7 cm new snow
CTM x 2 SP, ECTP14, down 50 cm, failed on 3-5 mm surface hoar
We found another non reactive layer that “propagated” the full 90 cm when we pulled our ECT column into the pit. This is a layer of decomposing graupel down 20 cm. No cracking, no whomphing, no other signs of instability.

No sings of instability. Large Surface Hoar growth.

CB Avalanche Center2016-17 Observations

Location: Crested Butte Area
Date of Observation: 02/05/2017
Name: JSJ
Subject:
Aspect: South East, South, South West
Elevation: 9,100-12,400

Avalanches:
Weather: Clear and cold at TH…5F @ 8am. Light winds from the NNW w/ Mod gusts at ridge top. Strong solar
Snowpack: No sings of instability. Large Surface Hoar growth found all the way to Mt. Emmons summit at 12,400’ where protected from wind. Strong solar today warming wind sheltered snow surfaces by 1200. Yesterday’s 10-15cms HST bonded well to underlying windboard and suncrusts.

Mountain Weather 2/6/2017

CB Avalanche CenterWeather

Date: 02/06/2017

Game On! Its coming back folks, we’ve got a large winter storm rolling in to start this week off right. This incoming storm look to keep this winter’s warm and wet trend going. We’ll see snow showers begin this morning with some discrepancy on today’s snow numbers between different models. The amount of lift and warm temperatures are leaving a bit of a spread in the forecasted numbers for today. Both winds aloft and moisture increase Monday night into Tuesday when the main event looks to take place. Winds will be from the west during this Monday night into Tuesday timeframe, favoring the western portion of the forecast area. Winds become northwesterly on Wednesday as snow showers taper and a ridge builds for a break in the weather heading into Thursday.

Today

High Temperature: 27
Wind Speed: 15-25 G40
Wind Direction: SW, W
Sky Cover: Overcast
Snow: 2 to 6

Tonight

Low Temperature: 21
Wind Speed: 15-25 G40
Wind Direction: SW, W
Sky Cover: Overcast
Snow: 3-6W/2-4E

Tomorrow

High Temperature: 27
Wind Speed: 15 to 25
Wind Direction: W
Sky Cover: Overcast
Snow: 5 to 9. (12 West)

Here we go again

CB Avalanche Center2016-17 Observations

Location: Cement Creek Area
Date of Observation: 02/05/2017
Name: ADB
Subject: Here we go again
Aspect: North, North East
Elevation: BTL

Avalanches: None. Just some rollers off skin tracks.
Weather: Blue bird: calm and clear even on ridgetop
Snowpack: Fields of surface hoar forming in lodgepole up to ridgeline. About 1cm in height.

On portions of skin track punched down to last layer of buried surface hoar. Ski pen: 18 inches.

Avalanche Level 1

CB Avalanche Center2016-17 Observations

Location: Crested Butte Area
Date of Observation: 02/05/2017
Name: Evan Ross
Subject: Avalanche Level 1
Aspect: North East
Elevation: 9,400-11,000

Avalanches:
Weather: Mostly clear sky, calm wind. Warm feel in the sun, but not quite as warm as expected.
Snowpack: SH on the surface in meadows. Burned off on steep southerly slopes. Didn’t observe SH on northeasterly slopes.

No signs of instability. Previous tracks in the terrain on plenty of steep slopes with no results. Skied near a couple week old crown in 3rd bowl. 1/19 SH had been cleared out where this previous avalanche had run, but was still preserved in avalanche terrain on the portions of the slope that hadn’t previously avalanched. 1/19 SH was down about 25cm under a soft slab. These slabs would budge in hand pits or where the slope was cut up between ski tracks. Still no avalanche results in the bigger picture.

1/19 SH down 25cm on the parts of the slope that hadn’t avalanched.

IMG_2200

Schuykill Peak/Pittsburg/Baldy

CB Avalanche Center2016-17 Observations, Snow Profiles

Location: Paradise Divide Area
Date of Observation: 02/05/2017
Name: Ian Havlick
Subject: Schuykill Peak/Pittsburg/Baldy
Aspect: North, North East, East, South, South West
Elevation: 9000-11700

Avalanches: No new avalanches, but obvious signs of <10″ diameter trees broken, and/or blown over 45º angles by a large avalanche off ESE face of Schuykill Peak this winter.  Impressive.  Also possible evidence of new/extpanded path in Democrat Basin this winter, (fallen/broken trees almost buried).
Weather: Mostly clear, increasing WSW winds throughout day, light to strong especially near and above treeline. Temperatures remained mid 20s at ridgetop, balmy close to 30ºF in valley bottom. Strong solar radiation.
Snowpack:

Decent wind transport, loading east facing slopes near and above treeline with <10″ windslabs, bonding well, no cracking, sluffing or signs of instability in new wind drifted snow or old snow.  Did observe spotty surface hoar at ridgetop, but wind was beginning to destroy.  Southerlies the SH was destroyed by radiation and wind.

Dug every 200 vertical feet or so on steeper (33-40º) NE facing slopes to get a sense for 1/19 surface hoar distribution. All profiles near and below treeline revealed concerning structure and slab behavior in long column tests. Consistent ECTP16-21 SP results and PST<30/100end 20170119 on 8-10mm standing, preserved surface hoar, 50-60cm deep, holding a F-1F slab above. Purposely dug on steeper convex rolls to examine structure if flushed previously, or not, and on all slope I dug, SH was still alive and well. Awaiting the big Mon-Weds storm (1-3″ SWE). This incoming rapid load is concerning, and the 1/19 surface hoar should NOT be written off yet, and still well within skier or sled triggerable range.  

Snowmobiled on southwestern facing slopes later in afternoon on south shoulder of Mount Baldy. Yesterday’s storm still generally soft and powdery at higher elevations, steep southerlies got moist and should be monitored for crust/facet combination below tomorrow’s storm.

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