Avalanche Advisory for Sunday, 3-4-2012

This advisory expires at midnight, Saturday 3-03-2012. 

All forecast areas of Tuckerman Ravine have Considerable avalanche danger today. Natural avalanches are possible; human triggered avalanches are likely. Two exceptions to this rating: the Lower Snowfields have Moderate avalanche danger, natural avalanches are unlikely and human triggered avalanches are possible, and the Little Headwall, which has Low avalanche danger.

Huntington Ravine has Considerable and Moderate avalanche danger today. Central, Pinnacle, Odell, and South Gullies have Considerable danger. Natural avalanches are possible and human triggered avalanches are likely. North, Damnation, Yale, and the Escape Hatch have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanche are possible.

We’ve got a fairly complex set of variables to wrestle with this morning, including recent weather history, avalanche activity, and forecasted weather, so bear with me as I do my best to distill these down into something useful. What we’re dealing with for snow stability is the aftermath of Thursday’s heavy snowstorm. In case you missed it, we received over a foot of light density snow while winds were out of the SE and E. Winds have since shifted back and forth from the W to the S and are currently from the W again. Summit wind speeds last night got very strong, gusting to 99mph (160kph), but we are suspicious that the strongest winds stayed aloft and did not push very far below the summit. The lack of wind-scouring in places such as Hillman’s is an important clue toward this suspicion. In Huntington the upper reaches of the gullies received some scouring, but the middle and lower sections were more loaded than we’d expect after this weather pattern. Meanwhile yesterday, the mountain warmed up and some freezing drizzle created a thin crust everywhere except underneath tree cover. Although it received some freezing rain or drizzle, the uppermost elevations of Mt. Washington did stay below freezing. The avalanche activity we can observe this morning is also less than we would have expected with yesterdays weather, and it’s difficult to determine when exactly these took place. I’m confident enough to say that numerous avalanches have happened in several areas since Friday night, when winds started to pick up.

So starting out today, we’ve got numerous forecast areas that are preloaded with fresh new slab. Based on recent activity, it’s a safe assumption to say these newly developed slabs have some existing instability problems. Currently, many places are in the upper end of the Moderate rating, such as midsections of Odell and South in Huntington and the Sluice, Lip, and Hillman’s in Tuckerman. Today’s weather forecast calls for a chance of additional snow, though only a trace to 2” (5cm) is expected and most of this will come in the afternoon as a weak cold front passes by. Winds will be from the W and decreasing in velocity, but I would expect the speeds to be sufficient to deposit any new snow onto the already loaded slopes. This will drive the avalanche hazard from the upper end of Moderate solidly into the realm of Considerable. Not only will naturally-triggered avalanches be possible, but the likelihood of a person triggering a slide will be elevated as well. If new snow accumulations don’t materialize, actual avalanche hazard in the Considerable rated locations will continue hover between Moderate and Considerable. If the upslope snow guns start up earlier and heavier than expected, then the trend will be toward increasingly unstable snow.

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 8:45a.m. A new advisory will be issued tomorrow.

Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2012-03-04 Print Friendly

Avalanche Advisory for Saturday, 3-03-2012

This advisory expires at midnight, Saturday 3-03-2012

Tuckerman and Huntington Ravines have HIGH avalanche danger today.  Natural avalanches are likely and human triggered avalanches are very likely.  Very dangerous avalanche conditions exist on a variety of slope aspects and angles.  Travel in avalanche terrain is not recommended, including run-out paths.  The only exception to this is the Little Headwall which has Moderate avalanche danger.

The old adage, “you don’t know where you’re going if you don’t know where you’ve been” is a perfect sentiment to capture our developing avalanche situation today. Let’s back up a couple of days.  On Thursday our most recent storm hit the mountains, dumping about 12” (30cm) on the Presidential Range.  Overall snow densities where light, averaging about 7% with the last 4” (10cm) being around 4%.  During and since that snowfall, winds have been quite light for Mount Washington, averaging about 28-29mph with brief gusts over 45mph on Thursday.  Through most of Friday, summit winds hovered around the 20 mph mark. Down at the horizon of the Ravines, at approximately the 5000ft level, wind speeds were less, leaving our new fluffy blanket fairly unaffected except in the more exposed locations. Then at midnight, several hours ago, snow began falling again with an increasing wind.  By 3:30am, Washington’s summit was averaging about 60mph, gusting to 74mph, from the South.  After relative calm period, I can almost hear it yelling, “hey guy’s I’m back, what’ya been doing?!”  Winds today are forecasted to shift, walking clockwise from the current S towards the W.  As winds shift to our prevailing directing and continue to build speed, our east-facing Ravines will get overwhelmed with the left over storm snow lying in the alpine zone.  This is particularly true in Tuckerman due to Bigelow lawn, a flat plateau the size of 600 football fields.  This area sits above the Ravine right in line for winds with a westerly component, providing an incredible supply of snow to be moved.  I would expect more than one avalanche cycle out of this event as slopes get reloaded, cocked to fire, and the trigger pulled by the final flake and gravity tugging on steep slopes.  The light densities will also make cross loading of S-facing areas easier than usual.  Although these slopes will not harbor the dangers of N and E aspects today they will still likely produce natural avalanches.  In areas such as Damnation and North, avalanche activity may be limited to smaller slabs and sluffs, but these can still easily knock you off a stance. To add to this entire situation, new snow has been falling over the last 4 hours and is expected to continue through the day, perhaps changing forms into a bit of a “precipitation grab bag”.  The summits forecast is for 2-4″ (5-10cm) of snow, sleet, and freezing rain, maybe even followed by rain. As these heavy forms of precip fall, any pre-existing instabilities will rapidly become worse.

All of this history and current weather translates quickly and definitively into today’s rating of “HIGH”.  All of our forecasted slide paths have fully developed tracks so you can expect full avalanche runouts to occur.  Although the light density snow can be easily picked up for transport today, crystals will be pulverized into small grains as winds increase, making for denser slabs packed in the deposition.  This increased mass may push some avalanches full path, criss-crossing the floor and approach fans of both ravines.  Travel in avalanche terrain, which includes run-out paths, is not recommended.  As blowing snow and clouds will offer very limited visibility, going into the Ravines just to look won’t give you much more than placing yourself as lead pin in the bowling alley.

The warmth that is expected today won’t last too long. Probably just long enough to make a mess of the nice snow at lower elevations, such as on the Sherburne Ski Trail where the lower sections are currently getting a freezing rain coating. Overnight, mountain winds will start to crank up, perhaps blowing over 100mph for a short time, then decreasing again into good wind-loading velocities. Tomorrow’s avalanche danger will depend in large part on avalanche activity today, more snowfall overnight and tomorrow, and whether or not the overnight winds were able pummel any gullies into full submission.

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 8:05a.m. A new advisory will be issued tomorrow.

Christopher Joosen, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856

2012-03-03 Print Friendly

Avalanche Advisory for Friday, 3-02-2012

This advisory expires at midnight, Friday 3-02-2012

 Tuckerman and Huntington Ravines have CONSIDERABLE avalanche danger.  Natural avalanches are possible and human triggered avalanches are likely.  Dangerous avalanche conditions exist therefore careful snowpack evaluation, cautious route finding and conservative route finding is essential.  The only exception to this is the Little Headwall which has Low avalanche danger. Natural and human triggered avalanches are unlikely except in isolated terrain features.

  Averaging our Harvard and Hermit Lake manual snow plots we picked up about 12” (30cm) of new snow from this storm.  We saw the evidence of multiple avalanches particularly in Huntington due in part to the gullies being a bit steeper in places and more water-ice present.  Sluffs occurring off of steep slopes and blue ice was the likely trigger for numerous very soft slab releases.  Our ridge top field time yesterday proved that our assumptions were correct, and we encountered very delicate soft slabs with little strength.  Storm snow densities averaged about 7%, however as the storm progressed densities decreased with the top 4” (10cm) only coming in at 4%.  This is important not only because it’s champagne powder under ski, but because it will be very easy to move with an increasing wind.  Summit winds are forecasted to escalate and shift from the current direction of W at 20mph to SW and 35mph later.  Only slight ridge top winds will be needed to move this low density snow down into the upper start zones to once again create delicate soft slabs loaded on loose unconsolidated snow.  This will increase the possibility of natural avalanche activity which has forced us to the “Considerable” rating decision.  A number of locations are currently at the upper end of the Moderate rating, but this should change through the day.  So the big bulls-eye factor to watch today is wind speed and EXACTLY what speeds they increase to.  If you notice any snow transport going on, even low ground level drifting; expect very touchy slabs to be developing. 

The other big news that I have been referring to over the past couple of days is the ramping up of wind velocities tonight and over the weekend.  Tonight winds will continue shifting to come from the S and increase to 60+mph (96kph) with more snow.  This is by far the highest speeds we have seen since the recent storm began.  These winds will whip up the blanket of alpine zone snow and pour it into avalanche terrain over a weak loose snow layer.  Then tomorrow, winds will shift back to the W and approach raging levels at 80 perhaps gusting to 100mph with more snow!  It is quite plausible the upper elevations will remain all snow from the precipitation tonight and tomorrow, with enough water equivalent to give up over 6” (15cm) of the white stuff.  I would anticipate “High” danger ratings for numerous locations on Saturday.  Check in to our “Weekend Update” later today for updates on this developing situation.

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 8:45a.m. A new advisory will be issued tomorrow.
 

Christopher Joosen, Snow Ranger      
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856
www.mountwashingtonavalanchecenter.org

2012-03-02 Print Version

 

Avalanche Advisory for Thursday, 3-01-2012

This advisory expires at midnight, Thursday 3-01-2012 

Tuckerman and Huntington Ravines have HIGH avalanche danger.  Natural avalanches are likely and human triggered avalanches are very likely.  Very dangerous avalanche conditions exist and travel in avalanche terrain is not recommended.  This includes the full runout paths for all slide paths.  The only exception to this is the Little Headwall which has Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible.

 A WINTER STORM WARNING is in effect until 9pm tonight.  Anticipated snowfall totals have slowly been ratcheting up over the past two days with current expectations of 5” (12.5cm) in the far north being likely and areas in the southern part of the State getting upwards of 15” (37.5cm).  Here in the White Mountains we will fall somewhere in between with 8-12” (20-30cm), with the higher elevations leaning towards the upper end of this forecast.  With 3 (8cm) of low density inches on the ground already we will continue to see snow all day and into the evening. This long duration event should deliver precipitation at a steady rate, producing another 5+/- inches (12.5cm) today and an additional 3-5” (7.5-12.5cm) tonight.  This will be brought to our terrain on SE winds peaking around 40mph before decreasing later today.  This will predominately load slopes and gullies with a northern facing component such as the start zones of Hillman’s Highway, Left gully, the Escape Hatch, South Gully, and Odell.  Cross loading of the Chute, Center Bowl, Pinnacle, and Central is also likely.  

Reaching the “High” danger rating should take most of the day with the majority of areas in the “Considerable “ range until this afternoon.  The aforementioned north to east faces will reach “High” first with south facing slopes like Right gully struggling to meet the “High” rating by dark.  A substantial factor in today’s stability assessment is the fairly light densities this morning at around 6%.  This will load into a soft slab that will have intact crystals due to the light winds and cold temperatures.  These slabs should be sensitive to triggers and be fairly weak, overall.  Even the slopes that are pointing into the wind should see sluffing in steep terrain and natural soft slab releases late in the day.  Expect sluffing to entrain loose snow and trigger very soft slabs on numerous aspects.  The later we get into the day the more I would avoid the concept of “just going into the Ravines to take a look.”  Expect the run out of a number of avalanche paths to criss-cross your intended route.  For example, once you pass the “Connection First Aid Cache” on the way into Tuckerman you will be in the run out of Left gully.

Winds are expected to wrap tonight through the W to the NW and then return to the SW tomorrow.  Velocities should stay light in the 30mph range on the summits continuing the formation of delicate soft slabs near the horizon of most start zones.  Wind speeds will pick up substantially over the weekend from our prevailing W and NW causing a new round of avalanche problems.    On a very upbeat note I would expect the Sherburne Ski trail to be pretty delightful over the next 2 days. This is a great way to kick off March, isn’t?

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 8:35a.m. A new advisory will be issued tomorrow.
 

Christopher Joosen, Snow Ranger     
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856
www.mountwashingtonavalanchecenter.org

2012-03-01 Print Version