Mountain Weather

CB Avalanche CenterWeather

Date: 12/21/2016

It’s a mild morning in the mountains, with temperatures in the 20’s over valley inversions below zero. A cold front is sagging into south into Colorado today under zonal flow, but it never really organizes across the Elk Mountains. A weak, closed low digging over Baja will start streaming moisture our way by tomorrow, and we should see a few inches of snow or more by Thursday evening.

washington gulch

CB Avalanche Center2016-17 Observations

Location: Crested Butte Area
Date of Observation: 12/20/2016
Name: J Banks
Subject: washington gulch
Aspect: North East, East
Elevation: 9,800-11,000′

Avalanches:
Weather: Winds L, variable in glades with MOD on ridgetop. no transport.
Snowpack: no signs of instability
2-5mm surface hoar

Wash Gulch

CB Avalanche Center2016-17 Observations

Location: Crested Butte Area
Date of Observation: 12/20/2016
Name: SB
Subject: Wash Gulch
Aspect: North East
Elevation: 9400 – 10800

Avalanches: No new avalanches observed or signs of instability during tour.
Weather: Clear, Calm
2F @ TH @ ~1100, w/ noticeable inversion
Snowpack: Ski Pen: 15 – 20cm throughout tour

Test Pit on 28* Slope on NE facing slope @ 10800′ showed following:
HS 120cm. 40cm of 4F facets @ ground, below 20cm of P hard rounds with preserved surface facets on top from early Dec cold/dry spell. 60 cm of progressively stronger rounds / DFs (1F to F) makes up the top.

ECTP14 down ~40cm within recent storm layer. No weak layers observed at this interface, just slight difference in hardness. Did not observe any other instabilities in this layer during tour.

Of more interest were the deeper weak layer interfaces (early Dec SF and DH). Failures here could be day-wreckers. After removing the top 40cm, we could not get a result after 10 very firm shoulder-level whacks.

12/20 Ob

CB Avalanche Center2016-17 Observations

Location: Paradise Divide Area
Date of Observation: 12/20/2016
Name:
Subject: 12/20 Ob
Aspect: North
Elevation: below tree line

Avalanches: None observed.
Weather: Sunny and calm.
Snowpack: No current signs of instability on north aspect below tree line. Southern aspects began to shed snow as exposed rocks and cliff-bands heated up. We did experience a number of sluffs on steeper terrain. Some were large enough to move a skier.

Red Lady Crown Investigation

CB Avalanche Center2016-17 Observations

Location: Crested Butte Area
Date of Observation: 12/20/2016
Name: Zach Guy and Scott Krankala
Subject: Red Lady Crown Investigation
Aspect: South East
Elevation: 12,200 ft

Avalanches: Investigated the skier triggered persistent slab avalanche in Red Lady Bowl, triggered 12/18/16 at approximately 3:30 pm.   The slab was mostly all 1F in hardness, or a hard slab. The avalanche was unintentionally triggered by skier, from what appeared to be a shallow, rocky part of the slope. The crown on the skier’s right side ranged from 200 cm to 30 cm in height, averaging approximately 150 cm. We did not go to the crown on the skier’s left side, but it appeared to average about 100 cm in thickness. Based on Google Earth measurements, the skier’s right crown is 200 feet wide and the skier’s left crown is 1,500 feet wide. The debris ran 3,600 feet and a vertical fall of 1,500 feet. The avalanche was medium relative to its potential extent. The debris snapped numerous small to medium sized trees in the runout, and was large enough destroy a car.   It failed in old, faceted snow and ran on the ground. The avalanche is classified as HS-ASu-R3-D3-O/G
Weather:
Snowpack: Our crown profile was 142 cm deep. The failure layer is 2 – 2.5 mm facets/rounding facets at the ground, F+ in hardness. The slab at that location is 132 cm, mostly all .2 to .3mm 1F rounds. We did not identify a crust layer at this particular spot.

Failure layer was a weak, old layer of facets and rounding facets. F+ hard, 2 – 2.5 mm in size.

The track of the skier who triggered the slide is on the lookers right side.

Extent of debris.

Looking northeast across the bowl.

The crown was up to 6 feet deep.

Looking down the slide path from the crown.

Looking up at the crown. Person for scale.

Crown profile.

 

More photos courtesy of Ben Pritchett

Oh-Be-Joyful Basin Crowns

CB Avalanche Center2016-17 Observations

Location: Crested Butte Area
Date of Observation: 12/20/2016
Name: Zach Guy
Subject:
Aspect: North, North East
Elevation: 12200-9200 ft

Avalanches: See photos. Got a humbling reminder that avalanche crowns are always bigger in person than viewed from afar, and I underestimated the size of some crowns in previous obs. The crown(s) in Redwell and the Shield are up to 8 feet thick (pencil hard slab over 1mm facets, 4F+ to 1F-). Debris ran impressively far into Redwell Basin. HS-N-R3-D3-O. The slide in Climax Chutes ran nearly full track to the valley and snapped trees. SS-N-R3-D3-O. The Red Lady crown is up to 6 feet thick. Report to come. Observed a dozen or more loose snow avalanches that ran naturally on sunny aspects today or yesterday, triggered by solar/warming. Mostly D1 to D1.5 in size.
Weather: Light winds, few clouds, mild temps.
Snowpack: We descended a NE slope above treeline that had flushed during the cycle with no signs of instability. These slopes now have thin snow coverage that will likely facet out again, making for greater variability in the alpine and some repeat offenders.
Dug two pits below treeline on NE aspects, one above a crown in Washington Gulch and one in Oh-Be-Joyful Basin. The crown profile showed, hard non-propagating results (ECTN25, BRK) on 4F facets near the ground.  The other showed hard, propagating results (ECTP27, SC) on F+ facets near the ground. Both slabs were about 80 cm thick.

Previously unobserved debris off of the west face of Gothic. Couldn’t make out a crown.

Redwell Basin Crown.

Crown above “The Shield” was up to 8 feet thick, pencil hard.

Debris from Redwell Basin slides reached the point where I took this photo from.

Observed a number of fresh loose snow avalanches today. And there is also a crown from the last avy cycle in this shot.

NE aspect BTL. ECTP27, SC on F+basal facets.

Extent of debris below Climax Chutes.

 

AIARE 2

CB Avalanche Center2016-17 Observations

Location: Crested Butte Area
Date of Observation: 12/18/2016
Name: Tim Brown
Subject: AIARE 2
Aspect: South East
Elevation: 9,200-11,000

Avalanches:
Weather: Cold! -11*C (12*F) @ 11,000′ ~ 2pm, Winds L, variable in glades with MOD blowing snow at ridge top.
Snowpack: Did not observe any avalanches (until we got back to town and saw the large avalanche in Red Lady Bowl).
No cracking, but our team produced 2 moderate collapses (~100′) in open meadows on SE aspects ~10,500′ and higher. No results from stomping on several test slopes. HS 90-120cm, HST 65-90cm

We dug a snow profile on a 15* slope on a SE-facing meadow at 10,800′ with HS 105cm, PF 40cm and PS 15cm to see how the snowpack was reacting to the massive new load:

Persistent slabs still problematic, especially in shallow areas: We were not able to initiate fractures by tapping on small and large columns with the full load on them (CTN and ECTX), but the snowpack showed potential for propagation when closely investigated with other snowpack tests. DTM SC and PST (End) 35/100 down 90cm on 1mm facets. Spooky!

Storms instabilities appear to be healing: we found 2 interfaces within the fist hard storm snow (2mm stellars down 25cm and 2mm graupel down 35cm), but no sudden results in CTs or positive results from ECTs.

Probing showed that the persistent slab structure is widespread in this area, but we found fast and soft skiing on low angle slopes no steeper than 30 degrees without incident.

emmons tour

CB Avalanche Center2016-17 Observations

Location: Kebler Pass Area
Date of Observation: 12/20/2016
Name: bc skier
Subject: emmons tour
Aspect: South East, South, South West
Elevation: 9500-12000

Avalanches: only past activity
Weather: beautiful
Snowpack: no signs of instability. was on top emmons, making final prep to ski bowl, noticed group of 5 skiers below on ridge. next time i looked up there were only 2 and 1 coming up towards top.. i could only assume other 2 had entered bowl below me, as i could not see them. i decided to avoid this group and ski south side. great pow, no one skiing in under me. great day!

Mountain Weather 12/20/2016

CB Avalanche CenterWeather

Date: 12/20/2016

A nice inversion has set up overnight with valley low temperature in Crested Butte at -15 while low temperature at 11,000 feet are much warmer around 20 degrees. We’ll see these valley temps rebound today and the 11,000 temperature rise slightly into the high 20’s. There is nothing to exciting going on in our weather forecast during the work week. We’ll see some building clouds tomorrow morning as a week trough brings the chance for a couple inches of snow to northern Colorado. Then we should see clearing skys Thursday into Friday before Santa Claus brings the next winter storm. We have few details and currently lots of variability with this weekend’s storm so we’ll have to wait for models to come into better agreement to talk those details.

Pittsburg

CB Avalanche Center2016-17 Observations

Location: Paradise Divide Area
Date of Observation: 12/19/2016
Name: EM
Subject: Pittsburg
Aspect: North, North East, East
Elevation: 9400 – 10500

Avalanches: Numerous from past weekends natural cycle which were partially filled in. no real recent activity in past 24hrs.
Weather: Cold air temps with generally calm air. Did notice on rare occasion small amounts of transport on highest most exposed terrain.
Snowpack: While traveling mostly on Northeasterly terrain I found the ski pen around 15 cm and boot pet around 40cm. Snow surface appears to be faceting from cold clear nights. Riding conditions were very supportive. Acended existing ski track but got off track numerous times in undisturbed snow and jumped vigoursouly without any noticeable collapsing.
At one location 10,100, ENE, 30*, open meadow in gladed terrain with minimal wind impact, I found an HS of 140cm. Test results were ECTx, x, N Brk at 88cm from ground on what appeared to be graupel/rimed particles. Whille conducting profile I was able to still identify buried NSF (likely dec. 6th) and two different graupel/rimed particle layers from recent snows. Although I didn’t get results on these layers during test, I was able to smash the column on ground producing planer fractures on the above mentioned layers.