Weekend Update for Friday, February 8, 2013

Snow sports enthusiasts around New England, heck, anyone who appreciates a proper winter storm from the comfort of the living room, is rejoicing and dancing in the streets today as two low pressure systems join forces to create a Nor’easter brimming with snow. If you are a member of the latter group, you’ll enjoy the media frenzy surrounding a powerful winter storm during a relatively slow 24 hour news cycle. The Weather Channel even went so far as to invent a naming system for winter storms where dates sufficed previously. The name Nemo seems to have gathered a following among other news outlets who are reporting on the storm frequently using this moniker (Disney clown fish or Jules Verne character, you decide). There was some discussion among our staff today that perhaps we can join in the fun and begin naming our weather events… Upslope Snow Frank. Wind Gust Samantha. But I digress, so we’ll agree to leave the fabrication of weather observation guidelines to the cable television channels and instead focus on the weekend outlook.

Friday’s forecasted snow totals were 2-4” in the valleys. By 1pm, 6” of very light density snow lay on the ground in Pinkham Notch. 6-8” of snow was reported on the trail to Hermit Lake. Early morning snow plot readings measured 3.3% density snow and though some riming was observed on falling crystals by early afternoon, the snow was still very light. This has some ramifications beyond mere snow trivia in a couple of ways. One is the tendency of snow this light to not adhere to anything, including itself. While windspeeds are in the low range this afternoon, the snow will sluff down ice and rock features in the ravines and pile up into deep slabs. Secondly, the snow will require much greater depth, in addition to time to form bonds, before it “sticks” to icy surfaces like the Sherburne and Gulf of Slides ski trail. “Dust on crust” will exist on icy surfaces through Friday in spite of the generous coating of “dust”. These factors, as well as the obvious ease with which light to moderate winds can transport snow of this density and form sensitive wind slabs are the root of our current avalanche concerns.

In case you’re considering venturing into the ravines this weekend, consider the situation. Deep light snow on winds that are wrapping around the cardinal points of the compass winds will create widespread avalanche problems on a variety of aspects. Add to this a thin snowpack more typical of December conditions with lots of rocks, trees and ice bulges at the surface, poor visibility due to blowing snow and temperatures near 0 F (-18C)and you have a dangerous combination of hazards to deal with up high. Anticipate an increasing avalanche hazard, possibly pushing into an Extreme rating, during the night Friday or early Saturday morning. If precipitation totals forecasted come to fruition and if slabs of snow remain to avalanche later, then a High hazard day on Saturday is quite likely. Sunday’s hazard rating looks like it will be elevated as well, particularly if upsloping, advection driven precipitation occurs as is often the case here when lingering moisture and winds work together to keep the party going on the heels of the Nor’easter.

Avalanche Advisory for Friday, 2-8-2013

Expires at 12:00 midnight, Friday, February 8, 2013

Tuckerman Ravine and Huntington Ravine will have Considerable avalanche danger today. Naturally triggered avalanches will be possible and human triggered avalanches will be likely. Careful snowpack evaluation, cautious route finding, and conservative decision making will be essential.

A WINTER STORM WARNING has been issued for today, tonight, and into early Saturday morning. Expect increasing avalanche danger during the day today. This afternoon and evening, snowfall rates will intensify, possibly reaching up to 3” (7.5cm) per hour. On Saturday, strong winds will keep avalanche danger elevated.

Well if you haven’t heard about the “Blizzard of ’13,” “Winter Storm Nemo,” or whatever other name some media outlet is calling this one, we’ve got a good winter storm brewing. The first snowfall is already hitting the ground on Mt. Washington. Storm totals are expected to be well over a foot, with the potential for 1.5 to2 feet (45-61cm). While the numbers themselves are impressive, winds will be the main driver of avalanche potential during and after the storm. Today, 25-40mph (40-65kph) winds are starting from the SW and will be wrapping through the S and eventually coming from the SE. This will begin the loading process on E and N-facing slopes, such as the Center Bowl, Left Gully, and Hillman’s, as well as Central, Pinnacle, Odell, South, and the Escape Hatch. These forecast areas will be the first to rise up into the Considerable rating. The early snowfall is very light density, which means soft slabs will have an easy time developing and eventually triggering naturally either in the storm layers or on the old crust. I’d say the chances are good that we’ll have some naturally-triggered avalanches before dark in some of these locations.

As the hours pass and darkness settles in, winds will continue to wrap around to the E as both the wind velocity and snowfall rates ramp up. This is when things begin to get really interesting. We’ll see cross-loading on the more northerly-facing slopes as well as those facing more to the S, such as Lobster Claw, Right Gully, North Gully, and Damnation. These areas will be rising through the Moderate range during the daylight hours, only increasing to Considerable late in the day. Unfortunately, they’re coming into this storm without a whole lot of snow in them, so they will need some time to develop further. The trend of increasing avalanche danger will keep going through the night and into Saturday; we’ll talk more about this in the Weekend Update tonight on our website.

That’s a lot of information, so here’s a summary to remember:

  1. Avalanche danger is rising today from into Considerable
  2. Slopes facing north and east will have more danger during daylight
  3. Slopes facing south will quickly catch up after dark
  4. Avalanches can kill you, so you’d best know what you’re doing if you are going near steep terrain today or tomorrow, including to the floor of the Bowl to “have a look.”

As for skiing the Sherburne, I’d wait either until the end of the day today or on Saturday. Before this morning, it was an icy mess. There were numerous patches of blue water ice, which are now hidden beneath 2” of 4% stellar crystals. You might as well be skiing with your eyes closed, because the only way you’ll see them coming is if someone else just wiped out on it just before you got there. On Saturday morning, you won’t want to be the very first one down. Let someone else lay a track in the flatter sections so you can keep moving.

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 8:35am, February 8, 2013. 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

2013-02-08 Print Friendly