Avalanche Forecast for Thursday, March 12, 2020
This information was published 03/12/2020 at 6:29 AM.
The Bottom Line
Generally safe avalanche conditions exist thanks to a refrozen snowpack that has eliminated most avalanche concerns. Small pockets of wind deposited snow may be found in sheltered areas, but should be easy to identify and manage. Avalanche danger today is LOW. Mostly cloudy skies today with temperatures staying below freezing will likely keep the snowpack firm, leaving long, sliding falls as the primary hazard today. These have resulted in many injuries over the years, often from stumbles due to inexperience. Crampons, an ice axe, and a helmet are great tools, but also bring skills to use them appropriately and recognize their limitations.
Yesterday, temperatures fell below freezing with mild wind. Less than an inch of snow has fallen since the Monday warm-up.
Today, temperatures in avalanche terrain should remain below freezing. No precipitation is expected until late tonight. Wind from the W will shift SW and increase from the current 25mph to around 50mph this evening. This southerly flow should bring moisture from the coast into the air, keeping cloud cover above 50% for the day.
Tomorrow will bring unsettled weather with a degree of uncertainty about precipitation types. Temperatures in our upper elevation band should approach freezing. Forecasts are calling for about 1” of liquid (though could be anywhere in the range of 0.5” to 1.5”) to fall on Friday, from midnight to midnight. It’s likely that rain, sleet and snow are all in the mix, particularly at lower elevations. Wind will be from the west and should increase to the 60-80mph range. Expect elevated avalanche hazard tomorrow.
Primary Avalanche Problem – Wind Slab
You may find small wind slabs in sheltered terrain. These rest on a refrozen crust. Wind slabs are likely well bonded to the crust, limiting the avalanche hazard for the day. It’s also possible that as the saturated snow on the ground was refreezing, new snow stuck to it, hiding the refrozen crust under a deceptive, thin layer of new snow. Snow surfaces may be deceiving from afar.
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.
Spring snow is all about timing and choosing the appropriate sport. Today is a day where the skiing conditions look less than promising while those with alpine climbing in mind could have a great day. Skiing refrozen chunky snow with the spotty pocket of wind slab sounds like a stressful day. Those looking for a fun adventure might consider taking advantage of the fast cramponing and go climbing, maybe even breaking the rope out sooner than normal to prevent the long, sliding fall. Despite spring conditions in the valleys, the mountains are just beginning their departure from winter and still demand your full attention.
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 03/12/2020 at 6:29 AM.
USDA Forest Service
White Mountain National Forest