This information was published 03/04/2020 at 7:07 AM.
NOT THE CURRENT FORECAST
This is an archived avalanche forecast.
The Bottom Line
Wind blown snow will cause avalanche danger to rise rapidly today. Natural avalanches will be possible due to the development of wind slabs in lee terrain where new and wind driven snow accumulates. Expect large drifts of snow to fail under their own weight or with the weight of a skier or climber approaching from below. Today’s snowfall is mostly limited to higher terrain so lower elevation areas will escape this wind slab problem. Avalanche danger will reach CONSIDERABLE with large natural avalanches possible in east facing ravines.
Yesterday afternoon, summit temperatures topped out at 30F and have been falling since that time. Mostly sunny skies allowed the warm March sun to affect most south facing surfaces at Ravine elevations, including Oakes Gulf.
Today, low pressure will bring 2-4” snow today to higher elevations. This snowfall will be accompanied by extreme west winds in the 70-90 mph range. Hourly recordings early this morning show summit wind speeds in the mid 80’s mph with moderate snowfall. Extreme wind and limited visibility will continue through the day with 1-3” more snow falling tonight with a wind shift to the northwest.
Tomorrow, temperatures will return to a more wintry state as winds subside and skies clear. The high temperature will be 10F with winds from the NW diminishing to 45-60 mph by early afternoon.
The recipe for today’s wind slabs:
Primary Avalanche Problem – Wind Slab
Wind slabs will reach peak instability today if snowfall forecasts pan out. Timing and size of natural avalanches will depend on rate and timing of snowfall but conditions seem on track to be dangerous by mid-day. The commonly taught ratio of 1:3-5 new snow to wind slab is typically more like 1:8-10 due to the terrain configuration of our range. Natural wind slab avalanches capable of burying a person will be possible in areas like Tuckerman Ravine and Gulf of Slides where a large fetch will maximize the amount of snow available for transport. Areas with a smaller fetch like Huntington and King Ravine may still produce natural avalanches, particularly if we receive the upper end of forecasted precipitation amounts, and will be easily large enough to sweep you off your feet. Summit fog and blowing snow will make terrain assessment challenging. Today is probably not a good day to thread the proverbial needle through our avalanche problem.
What is a Windslab Avalanche?
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Observations from the field yesterday are a reminder going forward into spring how quickly conditions can change as the sun tracks higher in the sky. Solar warming led to widespread rollerball activity on steep sunny slopes in Oakes and likely other areas where snow was soft. Fortunately the snow was not deep enough to entrain a significant amount of snow to cause more than a harmless loose wet avalanche from the Duchess and a few more on the right side of Tuckerman Ravine.
Today we return to a much more wintry scenario all too typical for the Presidential Range. Howling winds and upslope snowfall move significant amounts of snow and build tomorrow pencil hardness, firm wind slabs but not before passing through peak instability. Don’t underestimate the potential for a natural avalanche to occur and reach lower angle terrain. Today is not a good day to linger in an avalanche path or on the floor of Tuckerman Ravine like these folks did on a day with active wind loading a number of years ago. The outcome could have been much worse than it was that day.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch though conditions may be crusty as yesterday’s warmed snow refreezes.
Details on daily snowfall totals, precipitation type, total depth of snow and other information can be found on our page devoted to snow study plot data. Clickhere to check it out.
Recent snowpack and avalanche observations can be foundhere and on Instagram. Your observations help improve our forecast product. Please take a moment andsubmit a photo or two and a brief description of snow and avalanche information that you gather in the field.
Safe travel in avalanche terrain requires training and experience. This forecast 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.
Avalanche danger may change when actual weather differs from the higher summits forecast.
For more information contact the US Forest Service Snow Rangers, AMC visitor services staff at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or seasonally at the Harvard Cabin (generally December 1 through March 31). The Mount Washington Ski Patrol is also available on spring weekends.
Posted 03/04/2020 at 7:07 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest
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