Saturday, December 26, 2020

Some Thoughts on the Belleayre (New York) Avalanche

Yesterday afternoon, I learned via social media feeds and news reports of a possible early Christmas morning avalanche at Belleayre Mountain Ski Center in the Catskill Mountains of New York (see Avalanche damages lodge at Belleayre Mountain Ski Center from CBS6 News in Albany).  

Photos provided to CBS6 by Belleayre Mountain Ski Center show the damaged Overlook Lodge filled and surrounded by debris.

Source: Belleayre Mountain Ski Center via CBS6 News

Source: Belleayre Mountain Ski Center via CBS6 News

The ski center also reported that they were closed and that "supersaturated snow from the Yahoo trail let loose and slid into the Overlook lodge."

Source: Belleayre Mountain Ski Center

Belleayre is located in the Catskills of southern New York.  Those from the New York City area would describe it as "upstate," but it was definitely "downstate" for someone like me who grew up northwest of Albany.  

The ski center has a vertical drop of 1,404 feet and a top elevation of 3,429 feet.  The Overlook Lodge is a mid-mountain lodge (although you can drive to it) located at 2,542 feet and in the center left of the ski map below.    

Source: Belleayre Mountain Ski Center

Imagery from Caltopo shows the lodge near the base of Triple Chair #7 (click on image below to enlarge).  The colored slope angle shading (legend at upper right) suggests slope angles <27º immediately above the lodge with about 100 vertical feet with slopes of ≥ 27º and pockets ≥30º near the summit.  

Source: Caltopo.com

Under ordinary circumstances, one might say "c'est impossible!" for an avalanche to occur on this slope, but the circumstances leading up to the avalanche were hardly ordinary.  In fact, they were quite extraordinary.  In fact, it's hard to believe Santa was able to deliver toys to good girls and boys early Christmas morning! 

Let's begin, however, several days prior to Chirstmas.  The area received substantial snowfall on December 16 and 17.  Reports to the National Weather Service show that the heaviest band of snowfall followed I-88 from Binghamton to Albany, but reports near the ski center suggest anywhere from 12-24 inches in the area.  

A citizen weather observing site that provides data to MesoWest from Halcott Center near Belleayre and at a comparable elevation to the lodge (2254 feet) shows temperatures from 19-23 December between about 20 and 40˚F.  Data from the Claryville New York State Mesonet site (farther below) suggest a natural snow depth of about 8 inches on December 23rd.  However, on December 24, temperatures climbed steadily, peaking at around 57 or 58˚F early Christmas morning.  During this period, about 5 inches of rain fell in 12 hours.  


Source: MesoWest

Data from the New York State Mesonet site in Claryville tell a similar story with temperatures climbing on Christmas Eve and peaking at 57˚F at 5 AM on Christmas morning. At that time, the relative humidity was 94% and over 3 inches of rain fell in the prior 12 hours.  The snow depth at this site actually dropped to zero prior to the heaviest rain.  

Source: nysmesonet.org

So the weather was one of rapid melting and water loading of the snowpack at all elevations.  

With some effort, I found a photo online looking up the hill from the ski lodge on the New York Ski Blog Forum.  One can see a grassy area up the hill and then the track entering the lodge.  

https://nyskiblog.com/forum/threads/belleayre-conditions.658/page-7#post-7283

Based on this photo and the description on the Belleayre Mountain Ski Center web site, one possibility is that the grassy area represents the starting zone for the avalanche.  Most avalanches occur on slopes with angles of 30˚ or more.  It looks unlikely that the grassy area is >30˚, but some wet snow and slush-flow avalanches can start on lower angle slopes.  

Slush-flow avalanches in particular are major threats in some high-latitude areas of, for example, Norway, Iceland, Swalbard, and Alaska.  They involve mixtures of snow and water and I wonder given the heavy rainfall if what happened at Belleayre might be an example of one.  A recent review article from the Annals of Glaciology with some examples is available here.  

These are, however, educated guesses.  Boots on the ground to look farther upslope and investigate the snowpack and soil are essential.  It's easy to dismiss the potential for avalanches at eastern ski resorts, but they have happened.  Check out, for example, this paper presented at the 2004 International Snow Science Workshop entitled Man-Made Snow Avalanches in the Eastern United States.  Situational awareness may be valuable for future rain on snow events in the region.  

Comments from those with a deeper knowledge of avalanche mechanics and processes appreciated!
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4 comments:

  1. TomDecember 27, 2020 at 5:03 AM

    Thanks for the detailed write-up. Windham Mountain (about 20 mi NE of Belleayre) also reported avalanches during that storm: "...we had significant snow slides that took out hydrants on the snowmaking system and we are continuing with repairs on the upper mountain.". (See the 12/26 snow report on their Facebook page.)

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  2. AnonymousDecember 27, 2020 at 6:57 PM

    I'm hoping someone can gather some details like of the avalanche like slope angle,alpha angle, start zone shape, etc. Some idea of density of snow fall prior to the rain event would be interesting too. Rain on snow events are hard to predict or forecast and worth studying at every opportunity. Anyone with more details, please reach out to me at MWAC.

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  3. AnonymousDecember 28, 2020 at 6:39 AM

    That is a sweet looking little resort. Not sure how I missed it living back there. Probably drove by it 1000 times on way to an from NE resorts.

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  4. GregJanuary 5, 2021 at 1:46 PM

    My first thought is that it looks like a "glide avalanche" ..although after reading the slush flow avalanche abstract, I'm not sure there's a clear delineation between slush flow and glide avalanches.

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