Avalanche Forecast for Tuesday, March 10, 2020
This information was published 03/10/2020 at 7:23 AM.
The Bottom Line
Continued warm temperatures overnight and today has decreased snow stability on all aspects. Smaller sluff avalanches are possible on steep terrain, and should be easy to predict by watching for wet sloppy snow at the surface.
A greater hazard, though less likely is the possibility for a large wet slab avalanche. Wet slab avalanches are dangerous, and difficult to predict. Minimize your exposure to this hazard by reducing your time in and under avalanche terrain today.
Avalanche danger is MODERATE.
The uncertainty for when and at what elevation mixed precipitation turns to snow this evening includes the chance for snow totals to far exceed the forecast particularly in the evening. For climbers and skiers caught out after dark today, watch for developing new wind slabs in lee areas of the west wind. Snowfall rates could be intense, and new wind slabs would develop quickly.
Yesterday, skies cleared mid-morning allowing temperatures to rise reaching a high of 34 F on the Mt. Washington summit. Hermit Lake Snow Plot recorded 44 F for a high temperature. Wind from the W remained elevated at 55-70 mph.
Today, becoming cloudy with a chance of showers or a wintery mix in the afternoon, elevation dependent with a trace to 1” snow/ice forecast. As of 5am the summit temperature is 30F and all areas below 5000’ are above freezing. Temperatures will rise today pushing the summit to the mid 30’s F, before dropping this evening. Wind will be from the W at 50-70 mph. Tonight, mixed precipitation turns to snow with a trace to 2” or more possible.
Tomorrow brings colder temperatures in the lower teens, cloudy to partly sunny skies and W wind at 50-70 mph decreasing through the day.
Primary Avalanche Problem – Wet Loose
Wet loose sluff avalanches are likely to be initiated under your skies in steep terrain today. Watch for decreased surface snow stability as warm temperatures continue. This avalanche problem today will be driven more by ambient air temperatures than solar gain resulting in more widespread distribution on all aspects. Watch for pinwheels and rollerballs in steep terrain as a sign that wet loose avalanches are becoming possible. These will be small in size, generally easy to manage, though capable of pulling you off your feet. Consider the consequence of a wet loose sluff induced fall in your travels today.
What is a Wet Loose Avalanche?
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Secondary Avalanche Problem – Wet Slab
Wet Slabs are possible today at mid and summit elevations. Continued warming of the snowpack and rain or mixed precipitation adds one of the main ingredients: water. Water flowing though or beneath the snowpack is a recipe for wet slab avalanches. Respect avalanche terrain and runout zones for this low probability high consequence hazard that’s difficult to predict.
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.
Both of today’s avalanche problems are based on liquid water in the snowpack. Wet Loose avalanches are easy to predict as warmth penetrates the snow surface in predictable ways. Looking at the Hermit Lake Snow Plot this morning, we can see that snow temperatures are at 0F down to 20cm so we know that snow melting and water are present down to 20cm. Given the temperatures seen at other locations and elevations it seems clear that similar warming likely exists in widespread areas.
For the wet slab avalanche problem we need water moving through the snowpack, and some weakness or ice crust within the snowpack that the water can use to initiate a failure. It’s true that the current snowpack is strong, with good structure in most places though with as much as .7” of water in the forecast the thought of known buried ice crusts creates the possibility that merits the inclusion of this avalanche problem today.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. A few dirt patches are showing low on the trails.
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 03/10/2020 at 7:23 AM.
USDA Forest Service
White Mountain National Forest