Spring Travel Advisory 2015

CB Avalanche CenterAvi Blog, Avi-Off-Season

Issued 4/6/15 by CBAC

Spring season is a great time of the year to get into the mountains and generally offers better stability and more manageable avalanche problems for backcountry travelers.  However, avalanches conditions can still be dangerous during spring, and there are several kinds of problems you should continue to monitor and assess in you springtime adventures.

 

-Storm instabilities

Spring snowfall will usually fall on some form of crust.  These surfaces do immediately bond well.  Anytime a slab of new or windblown snow forms, expect touchy conditions during and shortly after the storm.  New snow becomes especially sensitive as the sun comes out immediately after the storm and quickly consolidates into more of a storm slab.   Expect leeward and crossloaded features at higher elevations to hold thicker and more sensitive windslabs  following a storm with moderate or strong winds.  These kinds of instabilities are generally short-lived during the springtime, but can last for several days after the storm on shaded aspects or higher elevations. The best strategy is to monitor how much snow accumulates during a storm and ease into small and manageable terrain until you’ve assessed how large and how sensitive new slabs are.  Be wary of windloaded slopes and avoid heavily windloaded features following a significant storm.  The Schofield Pass SNOTEL, which is northwest of town, and the Butte SNOTEL, which is on Mt. Crested Butte, are local remote snow sensors that update hourly.  Storm or wind slabs are most problematic over consequential terrain with cliffs, gullies, long vertical, or rocks and trees.

-Wet avalanches

When the sun (or rain) comes out after a spring storm and moistens the new snow, loose wet avalanches become frequent on any slope steeper than 35 degrees, and these point releases typically fan out and entrain all of the new snow down to previous crust layers.  These are usually small and predictable, but can carry significant mass after a large storm or in terrain with significant vertical relief.  They can also gouge deeper and grow larger entraining the full snowpack during prolonged warm-ups.   Wet slabs can be a larger and more dangerous problem. These are caused by liquid water percolating to and compromising the strength of buried weak layers.  This year, our snowpack is about a month ahead of schedule, meaning our April avalanche problems are more typical of May problems.  Most slopes facing east through south through west, as well as lower elevations that face north, have seen water run through the entire snowpack and have already been delivered the dry to wet “spring shock”.  These slopes saw a wet avalanche cycle in mid-March.  A number of these slopes have matured into a stable, spring snowpack, but it is difficult to identify which ones could still be harboring the threat of a wet slab.  Northerly facing slopes near and above treeline have seen less, if any, meltwater, and still primed for wet slab activity when temperatures and the higher sun angle turn on the water factory.  Last year, these slopes began their wet slab cycle around late May to early June.  The size of wet slabs failing on deeply buried weak layers will be likely be large at these elevations.  Wet slabs are most likely to occur during prolonged warm-ups and/or following multiple nights without a good refreeze.  If we see a dust-on-snow event, this will expedite surface warming.  Wet avalanche danger is usually lower in the morning and rises through the day. The best strategy is to exit avalanche terrain early during warm, sunny days or avoid it during rainy days.  Monitor how well the snow surface refroze overnight, and time your descent so that you are riding in a couple inches of supportive corn skiing, rather than punchy, trap-door snow or ankle deep slushy snow.  Look for evidence of recent wet avalanches on similar slopes to clue you in to dangerous conditions.  Monitor mountain temperatures from these weather stations and expect cloudy nights to prevent a better refreeze.

-Cornice Falls

Springtime is the season that large cornices that have been growing all season begin to weaken and fall.  These can also be triggers for slab avalanches.  Cornices tend to break wider than expected.  Give cornices a wide berth if you are traveling along a corniced ridgeline, and limit your amount of exposure climbing underneath cornices, especially during the peak of warming.

 

The CBAC will continue to monitor the snowpack and post updates to our website and our facebook page if conditions warrant.   The CAIC will issue statewide updates on Mondays, Wednesdays, and Fridays into the spring season.  

Red Coon Glade

CBAC2014-15 Observations, Avi Blog

NAME: Evan Ross
DATE: 2/23/15
LOCATION: Red Coon Glade
ELEVATION: 9,000-11,700ft
ASPECT: SE

WEATHER: Overcast sky was breaking up in the afternoon. A frew s-1 snow showers through out the day. Strong solar through thin clouds was creating a green housing effect. Calm wind throughout the day.SNOWPACK/AVALANCHE OBS: Green housing and some solar warmed the snow surface and created a 1-2cm crust by the afternoon. Had pits along the way found generally good bonding between the new/old snow interface as well as the new snow lacking a cohesive slab. HST at 11,000ft was 40-45cm. BTL south facing slopes grater then 30 degrees and below 10,000ft where bare of snow before this storm.

Ski cuts on a small shaded slope BTL that was about 35 degrees produced small storm slab avalanches on the old snow surface about 15 feet wide.
Observed several loose snow avalanches on a steep easterly slope near treeline that looked to set down into the facets below. These D1.5 sloughs may have failed naturally or where skier triggered from the ridge above.

Absurduary: A look at our warm and dry start to 2015.

CB Avalanche CenterAvi Blog, Avi-Off-Season

CBAC Forecaster Zach Guy.  
February 12, 2015

In the past few weeks, I’ve seen streams emerge from high elevation basins, sunny slopes melt back to complete dirt, and a migration of locals towards the desert for mountain biking or sun bathing.  I’ve only lived in Crested Butte for four years, but this pattern seems so absurd for a high Rockies mountain town at 9,000 feet in elevation, that I dug into some historical weather to see how unusual this weather has been.

Since the New Year, we’ve been plagued by both snowfall drought and unseasonably warm temperatures.  The temperatures have been the greatest anomaly this winter.  billy barr in nearby Gothic has an exceptional record of temperatures and snowfall dating back to 1974 (www.gothicwx.org).  As of Friday, February 12th, 17 out of our 43 days this year have seen record-breaking high temperatures.  There have only been two days in February that didn’t break a temperature record, and we are currently going on 8 days in a row of record high temps. I expect the next two days will break records too.  On February 6th, the temperature hit 52 degrees F, which was a full month earlier than we’ve ever seen temps reach into the 50’s.  I think my brother in Florida is having a colder winter right now.

Looking towards Red Lady Bowl and some dirt slopes down lower.  Last year on this date, I dug a pit on a similar slope as that dirt slope in the foreground and found a 2 meter deep snowpack.


Snowfall droughts this time of year aren’t quite as unusual as the temperatures we’ve seen.  I looked at both Gothic snowfall and records from the town of Crested Butte, which date back to 1962.  (http://www.crestedbutte-co.gov)  In Crested Butte, where the average snowfall in January is 41.6”, we got 10.6” of snow last month.  There have only been four other January’s that saw less snowfall in the past 52 years.    February is off to a rough start as well, with only a few inches.  If it makes you feel any better, the winter of ’76-’77 only saw a total of 3” of snow from December through February in Crested Butte.  Too bad they didn’t have fat bikes back then. Gothic has fared marginally better on snowfall.  They saw 27” in January, which is 41% of average and the 8th lowest January on record.  Gothic picked up 6” in February, which is on pace to come up at 21% of the 70” average for February. Thanks to a healthy November and December, Schofield Pass SNOTEL is sitting at 67% of mean (3rd lowest snowpack in its 30 year record), and the Mt. Crested Butte SNOTEL is at 80% of its mean.

As someone who loves the winter, I can’t help but feel gloomy over the past couple months.  However, models keep hinting at a pattern change coming later this month or in March, for the warm and dry high pressure ridge to shift west and put us back into the storm track.  We’ll see…  And also worth noting, the horrible snow year of ’76 to ’77, which was the lowest on record at 61” in Crested Butte, was followed the next winter by the highest snowfall on record, at 381”.  I’ll stick around next winter to see what happens!

Looking towards Mt. Crested Butte.  Looks more like late April than early February.

Gothic Temps

CBAC2014-15 Observations, Avi Blog

Date: 2.7.15
Name: billy bar
Location: Gothic

Up until yesterday the earliest date in which the temperature in Gothic climbed above 10ºC (50ºF) was March 06.  Yesterday it reached 52ºF- beating that old date by  full month.

Snodgrass TH

CBAC2014-15 Observations, Avi Blog

NAME: Evan Ross
DATE: 1/31/15
LOCATION: Snodgrass TH
ASPECT: NE
ELEVATION: 9,650



WEATHER: Mostly cloudy sky in the afternoon. Snowing S-1 with warm temps that made it feel like it was almost raining at times. Calm winds started to increase from the west after 4pm.

SNOWPACK/AVALANCHE OBS: Snowpack was upside down with the new snow being cohesive, heavy and moist sitting on weak facets below. A pit at the above aspect and elevation. HS 86cm, all fist hard. HST was 10cm deep and cohesive. Jan 11th Surface Hoar was down 25cm. Shovel tilt and CT test produced moderate results on the Jan 11th interface. ECTX as the snow structure was soft and weak.