Dec 192014
 

Posted 5:35pm 12-19-2014

Welcome to the 1st of many “Weekend Updates” this season.  If you’re new to this product we put this out each Friday afternoon/early evening when we are using the US 5 Scale Danger Rating system.  We believe there is a lot that can change in the 12 hours from the Friday morning advisory and the evening Update, particularly with the weekend weather predictions. Allowing one or two model runs (depending on which MOS model) to come out during the day can really make a difference. Our intention is to provide the latest data we are aware of so you can make better travel plans for your weekend.

A few days ago I wouldn’t have predicted we’d have a High avalanche posting out yesterday and fracture lines peppering the terrain today due to natural avalanches.  Why?  Because on Wednesday morning the mountain succumbed to a quick burst of unpredicted 2” an hour snowfall rates for 3-4 hours.  By 1045 the sweat was rolling off our foreheads wondering if this was going to continue all day, it didn’t.  But by midnight on Wednesday the summit recorded 9.5” with an additional 7” by noon yesterday.  After my time in the field with Frank today we surmised that areas below the upper part of the summit cone received much less than the 16.5” the Observatory recorded.  This is not unusual per se, but it made avalanche forecasting difficult coupled with the complicating cloud cap and no visibility.

The cloud cap today made us wait and hope that visibility would improve so we delayed until late morning when we pushed through the clouds hoping for an undercast.  We had brief windows of clarity in Tuckerman to get some pictures before the veil rolled back in.  (See more on our facebook page).  We will post Huntington shots tomorrow when clear skies prevail.

First picture is Tuckerman’s Right Gully and the Sluice

2014-12-19 The Sluice and Right Gully

2nd-Sluice through the Headwall

2014-12-19 The Sluice-Lip and right Center

3rd-Close up of the Lip and the Right-Center Headwall

2014-12-19 The Lip Fractures

4th the left  Headwall over the Left Gully

2014-12-19 The Chute Fracture and Left Gully

We decided that presenting numbers and tests would do little to help due the amount of spatial variability around the mountain.  Clearly the pictures demonstrate numerous fracture lines.  We think these avalanches occurred naturally, likely late on Thursday a bit before the peak wind of 98mph. Some have reloaded a bit, others have not.  If you look closely at the Lip fractures you’ll see a number of small reloaded pockets from sluffs and windloading.  Under the Chute fracture just to the right of Left Gully you’ll find less re-loading, but more hangfire and threat above.  In between across the Center Bowl you see a mixed bag of scouring, loaded pockets, avalanche bed surfaces, and of course cliffs and ice.

Generally you should see areas fall one avalanche danger rating or more tomorrow.  In Tuckerman a skilled traveler can find a climbing route that seasoned individuals would find acceptable in relation to avalanche risk.  That said, a group giving no attention to mitigate avalanche risk could find locations with enough instability to respond to human triggers causing an avalanche.  Once again, you got it!…….spatial variability.

Often the skill of visual assessment and the clues we can get from using our eyeballs are under estimated.  Yes it’s true that stability assessments can require digging, but as in all things rarely does one source of data give you the entire picture.  When standing and staring at the terrain ask “why does the snow look like that?”  It is somewhat of a hidden or lost art that we should revive.  This is regularly highlighted for me on Mount Washington due to how much wind sculpts the winter landscape.  Today it was once again an important skill viewing deep runnels, fracture lines in different states of reloading, a thin rimed surface, smooth and creamy areas, rough and punished locales, knocked over brush and floor debris, etc. the list goes on.  Check out this book if you’ve never seen it. Ed LaChapelle is one of our avalanche mentors but this book is one of his lesser known works although certainly a winner! I’ll do a book review of it later this week and post on “the pit”.  A great resource of a lost visual skill.

Secrets of the Snow

Something to remember with weekend weather forecasted to deliver ample sun and low winds, that many avalanche accidents occur in these conditions because we forget to be critical thinkers.  Everything just seems so glorious.  Beware of the human factors and heuristic traps we can fall into on these blue bird days.  The snowpack doesn’t care that it’s beautiful it will do what it’s set up to do.  Have a great weekend and check the avalanche advisory in the morning.  Chris

 Posted by at 5:39 pm
Dec 192014
 

This advisory expires tonight at 12:00 midnight.

Tuckerman Ravine has CONSIDERABLE and MODERATE avalanche danger. The Sluice, Lip, Center Bowl, Chute and Left Gully have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation, cautious route-finding and conservative decision making are essential. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.

Huntington Ravine has CONSIDERABLE and MODERATE avalanche danger. Central, Pinnacle, and Odell Gullies have Considerable avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. Careful snowpack evaluation, cautious route-finding and conservative decision making are essential. All other forecast areas have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.

AVALANCHE PROBLEM: Wind slab is our primary avalanche concern again today. New snow and increasing wind speeds yesterday created hard wind slab in many areas. Where these wind slabs exist, they are likely to be hard, fairly thick and capable of propagating a crack on a slope above you. In other areas more sheltered from the strongest NW winds, softer Storm Slabs mixed with the wind slabs may also present a problem. Travel very carefully to avoid these unstable slabs as well as the paths and terrain traps beneath them.

WEATHER: Visibility today, though improving, will be hit or miss as remnants of this last low pressure system clear out. Temperatures will rise to around 20F (-7C) with light to moderate wind from the north in the 25-35 mph (40-55 kph) range. Gusts, potentially to 45 mph (75 kph), will keep things cool but should allow for a decent summit day. Don’t forget that we are approaching the shortest day of the year with around 9 hours of daylight with which to get things done. Sunset is at 4:07 pm.
SNOWPACK: Yesterday snowfall rates continued to impress us adding 6+” (15+cm) by noon, totaling 16.6″ (42cm) for the storm event.  Wind speed increased from the NW during the early morning hours on Thursday and ramped up over several hours moving snow from the alpine zone, mixed with new snowfall, into aspects with an eastern component.  Undoubtedly some crossloading occurred on slopes perpendicular to the prevailing NW direction.  We believe new slab density increased as wind speeds climbed through daylight peaking around 6pm creating an unstable snowpack with dense over lighter slabs.  High volumes of snow were transported into most forecast areas creating a peak instability more than likely close to the twilight hours. Velocities dropped all night to a current of 18mph.  As winds fell back down below about 50mph around 10pm, the vast majority of loading shut down.  This information has us less focused on natural avalanche activity, but based on the cold temperatures and short duration for natural settlement humans have a possible to likely chance of triggering slab avalanches. Expect slab densities and instability to change depending on whether or not slopes were exposed to high NW winds. You may start ascending on heavily wind scouring locations down low and then move into much lighter and unstable slabs as you approach protected terrain features.

Both Ravines are still encapsulated in clouds so we are unable to verify where avalanche activity occurred or what forecast areas received more snow than others. However, historically the locations posted at Considerable today receive the most volume, harbor higher slab instabilities, and require more caution from weather events similar to the last 48 hours.  We expect clouds to begin clearing soon allowing us to get into the terrain for new data collection that will get posted in the Weekend Update late in the afternoon.  In the mean time expect cold slabs to be unstable and hold the ability to propagate a fracture.  With bluebird days approaching with light winds watch yourself and the heuristic traps we can fall into when we are basking in what appears to be an “unbelievably awesome” day. Anticipate lingering instability in the high mountains this weekend.

Please Remember:

  • Safe travel in avalanche terrain requires training and experience. This advisory is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
  • Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast.
  • For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.
  • Posted 7:50 a.m. December 19, 2014. A new advisory will be issued tomorrow.

Frank Carus/Christopher Joosen, Snow Rangers
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2014-12-19

 

 Posted by at 8:04 am