Avalanche Forecast for Thursday, February 7, 2019
This information was published 02/07/2019 at 7:00 AM.
The Bottom Line
A mixed bag of hazards will face anyone heading into the mountains today. On the list of concerns are a refrozen, long-sliding-fall type of snow surface, new sleet and freezing rain, and temperatures hovering around freezing. To top it off, fog will reduce visibility up high. New precipitation and warm temperatures keep some concern for wet slab avalanches on the radar. Wet slab and loose wet avalanches are unlikely today, though warmer than forecast conditions could increase the potential a bit. You’ll find microspikes really helpful today on area trails, with crampons, ice axe and a strong ability to stay on your feet necessary for safe travel in steeper terrain. LOW avalanche danger will exist at all elevations and aspects today.
Yesterday, sunny skies and warm temperatures prevailed until mid-afternoon allowing a few folks to enjoy an early corn harvest. Snow only softened on sunny aspects at mid and upper elevations as temperatures reached only to around 30F on the summit. Last night temperatures dipped to 23F as clouds and another round of mixed, but mostly frozen, precipitation fell last night. At this time, it looks like half an inch of snow fell on the summit and the rest was sleet, totaling .24” liquid. Today will bring a mixed bag of sleet and freezing rain and possibly snow, though only a trace amount is expected. A high of 33F on the summit along with light winds from the W then SW at 25-40 mph then 10-25 mph. Summit fog and clouds will hamper visibility through the day. Rain returns tonight before cold weather returns Friday with some snow and high winds.
Primary Avalanche Problem – Wet Slab
If you have to pick an avalanche problem today, wet slabs would be the closest fit. Temperatures rising above freezing will keep this on the list of hazards but the potential for long-sliding-falls is jockeying for first place on the list. The largest and steepest slopes carry the greatest potential for a larger, though still unlikely, avalanche in what have proven to be unreactive surface slabs.
What is a Wet Slab Avalanche?
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
Someone threw the brakes on the snow train after the mountain received 60” of snow during the month of January. Average for the month is 44”, with 40” average in February. So far, one week into the new month, we’ve received just 2.8” of snow. Though the sun tracked across the sky in a winter-like trajectory yesterday, sunshine and warm temperatures allowed some softening on sunny aspects. Signs of the recent warm-up were everywhere with glide cracks beginning to open and tracks on the surface from falling ice in the Headwall. While some dry snow existed deep in the snow, it was beneath a thick ice crust in the limited number of areas that we dug in Tuckerman and Huntington Ravine. While we aren’t fully isothermal yet, given the refrozen surface and stout crusts deep in the snowpack, our avalanche problems would require significant amounts of rain or meltwater to raise concerns.
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 02/07/2019 at 7:00 AM.
USDA Forest Service
White Mountain National Forest