Avalanche Forecast for Thursday, January 30, 2020
This information was published 01/30/2020 at 7:07 AM.
The Bottom Line
- Continued drifting of snow yesterday and cool temperatures have preserved the existing wind slab problem.
- Wind slabs vary in size and reactivity to human triggering in the eastern half of the compass rose with many of these areas able to produce an avalanche that could bury a person.
- Evaluate snow carefully today and remember that wind slabs can fracture higher on the slope above you.
- MODERATE avalanche danger exists where you find these wind slabs in mid and upper elevations. LOW avalanche danger exists in wind scoured areas, places that snow is covered by the ice crust and at lower elevations, which have much less snow.
Wind will shift to the west and diminish in speed this afternoon. Another bright sunny day is on tap, with less wind transported snow in the air than yesterday. Summit temperatures will be in the teens F where the mercury already sits at this hour. Wind will drop to the 15-25 mph range today.
Primary Avalanche Problem – Wind Slab
Softer, weaker snow exists under these wind slabs. This density change makes these slabs prone to human triggered avalanches. The largest but also most stubborn slabs sit beneath steep areas mid slope where wind has deposited snow from higher on the slope. These slabs also exist in gullies with a south and north facing aspect due to cross-loading. Several parties turned around and changed objectives yesterday due to the poor snow structure, cracking and sensitivity of these slabs.
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.
Plumes of wind driven snow were visible at ridgetops through the day yesterday as gusty wind moved dry snow into north and east facing aspects, while cross-loading others. Hourly observations overnight suggest that wind speeds remained high enough to continue to move snow through the early morning hours despite the fact that blowing snow was not written in the observation record in the past 36 hours. Field observations and snow pits revealed only a fair snow structure that exhibited moderate stability…certainly nothing new for our wind slab driven snow regime. This prevalent problem confounds skiers particularly since the best snow for skiing also happens to be the avalanche problem. Be sure to dig today and remember that last Saturday’s ice crust will be the ultimate bed surface for an avalanche though the weak layer is likely to be higher in the snowpack. This could make an avalanche larger than you might expect.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. A generally warm winter has left open water in many areas, including water bars and often skiable drainages such as Monroe Brook.
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. Click here to check it out.
Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit 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 01/30/2020 at 7:07 AM.
Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest