First, I realize this is going to be a slightly tardy and generally brief Weekend Update. We’ve had a busy day on the mountain today. There were human-triggered avalanche incidents in each ravine today. More information will be forthcoming later in the weekend about these incidents. Right now my main goal is to talk about what visitors can expect on Mt. Washington this weekend. Obviously, there are some stability problems lingering, so let’s start with a recap of the past week.
On Wednesday, the latest Nor’easter rolled through, dropping 15” across higher terrain and just shy of 12” at Hermit Lake. Winds blew first from the ESE during the storm, then went dormant for a day before re-emerging last night from the NW at 30-40mph. Both the ESE and NW were responsible for loading snow into many of our forecast areas. The biggest concerns stem from last night’s winds, which were able to load up S-facing and E-facing slopes. These include many of the forecast areas of both ravines.
Today the forecast was calling for some light snow, which we did receive but it amounted to very little. Additional loading was kept at bay as the winds dropped down below forecasted speeds to around 15-20mph. I was on Lion Head ridge today, above Right Gully and Lobster Claw, and only saw the slightest amount of airborne snow. However, I did take notice that there is an awful lot of snow sitting in the Alpine Garden, waiting for either an increase in wind speeds or shift in direction. When that happens, there will be a significant loading event into lee areas.
Weather this weekend will be much like what we had today…in the clouds with chances for snow showers both Saturday and Sunday. Winds will be rather light for Mt. Washington. This will hold true until Monday or so, when we should start to see wind speeds rise.
So if you’re looking for a hike up Lion Head or other route that sits outside of avalanche terrain, the biggest environmental hazard you’ll face is low visibility. This is not to be discounted, though. Blowing snow and clouds can be very disorienting. Bone up on your map and compass skills tonight before heading up into the clouds.
If you’re looking to get into avalanche terrain, remember there are existing instabilities on the mountain in many areas. Recent avalanche activity is a solid indicator of unstable snow, and we had two incidents this afternoon. To make matters worse, additional new snow won’t need very strong winds to be loaded into wind slab on lee aspects, and with lighter winds these tend to form in the middle and tops of the gullies.
Personally, I would let the steep snow sit for a couple more days before testing it out. Here are a couple photos I took from the slide in Lobster Claw. The slide took place in the skier’s left fork, and the other one equally loaded, so don’t think for a minute that walking up to the debris pile to take a look at it is completely without risk.
This is just below the fork in Lobster Claw. The flow pulled out additional slab on the climbers left side of the gully. This crown is 34cm deep, has 10cm of new slab on top, 2cm of frozen sun crust, a thick layer of soft slab, and slid out on an older sun crust from Monday.
Here Frank is climbing above the fork, in terrain that is often mistakenly thought to be “safe” terrain. We found debris had pushed up onto the upper gully ridge farther than expected. The debris ran almost to where the hiking trail passes below the gully, in one location it was at least 8-10′ deep piled up against a tree.
So you think the bushes in the tops of gullies act as anchors? Think again. In these cases, they act as weak point and fractures tend to propagate from one weak point to another. This slide linked up the entire start zone of the right fork of Lobster Claw, and stepped down a few times after initially releasing.
This advisory expires at 12:00 midnight, March 1, 2013
Tuckerman Ravine and Huntington Ravine have Moderate avalanche danger. Natural avalanches are unlikely and human triggered avalanches are possible. Evaluate snow and terrain carefully. The only exceptions to this rating are the Lower Snowfields and the Little Headwall, which have Low avalanche danger. Natural and human triggered avalanches are unlikely.
There are two contexts in which to be looking at snow stability today. First is related to the after-effects of the recent storm, i.e. existing stability problems. Next is how the weather forecast is going to play out, with the potential for increasing avalanche danger due to new snow and additional wind loading. Overall, this is a complex snowpack that deserves respect. If you know what to look for you may be able to seek and find reasonably stable snow, or you might find snow that scares you more than the threat of sequestration ever would.
Without getting too deeply into the weeds about how exactly the storm played out, I think it’s accurate to say that the mountain fared well. Approximately 15″ (38cm) of snow fell on the summit and we saw a little under a foot at Hermit Lake. During much of the storm, winds were strong from the ESE. Yesterday, they shifted to the NW but died off into the single digits for many hours. Overnight wind speeds rose again into the 30-40mph (50-65kph) range from the NW. Current stability problems can be found on many aspects. Those with a north-facing component were loaded during the ESE winds and snowfall; those with an E or S aspect saw further loading last night while winds blew from the NW. S-facing slopes such as Right Gully received solar gain and had a moist surface layer yesterday. Some forecast areas, such as the Lip, Center Bowl, Central, and Odell Gully will be at the upper end of the Moderate rating. Remember that the topography of our ravines creates conditions with high variability as you move from one location to another. This phenomenon is heightened when winds have been shifty and the sun is at work. You should be carefully assessing snow throughout your entire route. If solar energy is able to penetrate again today, there may be some stabilizing effect on S-facing slopes.
The issue of today’s weather will need to be on your mind as well. This is what might cause avalanche danger to exceed the posted ratings in some locations. Currently there is some snow being blown down the Lip and headwall of Tuckerman and in many gullies of Huntington. We don’t believe this additional loading on its own is enough to bump ratings into Considerable, but it is slowly accumulating and adding load to existing slabs. Furthermore, a light amount of new snow may fall today. It’s hard to believe this when you look up from Hermit Lake and see clear blue skies, but the NWS forecasted about an inch and the Observatory forecasted 1-3″. Based on what we’re seeing, we think 1″ is the more likely scenario. But, if we do get more than that today and winds are blowing from the NW at 30-40mph, the instabilities mentioned above will continue to develop. This may push danger ratings above Moderate in some areas. If we get nothing at all, then we will remain in the Moderate range.
The lower half of the Sherburne went above freezing for a little while yesterday. Expect varying conditions from top to bottom.
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., March 1, 2013. A new advisory will be issued tomorrow.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forests
(603) 466-2713 TTY (603) 466-2856