Avalanche Forecast for Tuesday, February 26, 2019
This information was published 02/26/2019 at 7:09 AM.
The Bottom Line
New wind slabs that are possible to trigger should be your primary avalanche concern if you brave the extreme wind and frigid temperatures today. Continued wind loading on these new slabs should also keep natural avalanches initiating in steep overhead terrain on your radar. While unlikely, recent snow and loading make it prudent to assume a natural avalanche could occur in locations with the greatest upwind fetch until you can determine otherwise. Wind affected snow can be found at lower elevations where you’re most likely to find reactive wind slabs today. MODERATE avalanche danger exists for all forecast areas. Make careful observations of our variable upper snowpack to guide your terrain decisions today.
Snowfall yesterday and last night ended around midnight, totaling over 8 inches at the summit with less at lower elevations. Wind from the W and NW has been sustained at over 100 mph on the summit for all but a few hours since late Sunday night. Several hours last night were in the 120-140 mph range with a peak gust of 171 mph. Today and tonight wind should remain NW around 80 mph with temperatures in the teens below 0F. A trace to one inch of snow is forecast as clouds decrease today. Expect no snowfall tomorrow as wind speeds finally drop significantly.
Primary Avalanche Problem – Wind Slab
Fresh wind slabs are the primary avalanche problem for all elevations today. You’re most likely to find them on the eastern half of the compass rose, with stubborn slabs at middle elevations and the potential for reactive but smaller wind slabs at lower elevations. No recent visual observations of higher terrain combines with wind continuing to affect the upper snowpack to provide a healthy dose of uncertainty today. Look for smooth wind drifted snow to identify the avalanche problem wherever you travel today and expect great variability in the wind’s effect on the snow surface.
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.
The notable wind event that is tapering slightly but continuing today will make for varied upper snowpack conditions of hard wind slab, heavily wind textured snow, and scouring to old crusts. You can also expect to find wind affected snow at low elevations which is also where you’re most likely to find reactive wind slab today. The unique recent weather factor was continued snowfall with significant accumulation on the extreme wind yesterday and last night. This somewhat rare occurrence of significant snowfall through peak wind speeds of a storm lends uncertainty to today’s forecast. We will undoubtedly have an interesting aftermath of this snow and wind event when visibility returns. Continued wind loading today should couple with potentially wide spatial variability in motivating you to carefully and continually assess snowpack if you venture into steep terrain.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
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 02/26/2019 at 7:09 AM.
Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest