Avalanche Forecast for Friday, March 29, 2019
This information was published 03/29/2019 at 7:12 AM.
The Bottom Line
The warming trend will continue today along with the chance of minimal precipitation. Skiers and riders should be aware of managing wet loose sluffs on steeper slopes today. While likely to be small in size, these can be hard to escape and cause trouble if they drag you over a cliff or ice bulge. Temperatures should stay below freezing at upper elevations, preserving dry snow in the form of wind slabs for at least another day. LOW avalanche danger exists for our forecast areas. While wet loose avalanches may become possible if the weather varies from today’s forecast, their size should remain small.
While the warming trend continued yesterday on middle and lower elevations, our highest elevations are continuing to see below freezing temperatures. Highs at our snowplots yesterday reached 40F at 4370’ (Grey Knob) and 43F at 3800’ (Hermit Lake). Today will be mostly cloudy with a chance of precipitation through the day. Elevations above 5500’ should see all snow, though only up to 1” of accumulation. The rain/snow line will be somewhere in our mid elevation band. Rainfall totals today should stay under one tenth of an inch. Currently at 3500’, the temperature is 34F with highs forecast to reach into the lower 40s. Light precipitation should continue tomorrow with temperatures cresting the freezing mark at all elevations.
Primary Avalanche Problem – Wet Loose
Lower and middle elevations will pass 24 hours of above freezing temperatures this morning. Cloud cover will minimize solar gain today, but with temperatures rising to 40F in places, wet snow will be found on all aspects below 4000’, especially in shallow areas of the snowpack or near large rocks and trees. This will most likely present itself as a sluff management issue. While these should be small in size, wet loose avalanches can easily push someone over a cliff if this occurs in the wrong place. An easy way to manage this problem today is moving to lower angled slopes is you find yourself sinking into mushy snow.
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 – Wind Slab
Wind slabs exist on easterly aspects in our terrain above the freezing line of about 4000’. These are firm in nature, though may be softer in the protected areas of terrain features. Up to one inch of snow is forecast today on 30-45 mph wind from the west. Be on the lookout above 4000’ for this new snow if it accumulates through the day. Larger wind slabs that formed one week ago are have stabilized and are now unreactive to human triggers
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.
Weather forecasts are calling for the rain/snow line to be around 4000’ today. Skiers yesterday reported this elevation being the approximate defining line between wet snow and dry snow on southerly aspects. Aspects that received solar gain yesterday saw significant warming with snow becoming wet down to boot tops. With warming today being driven by temperature rather than solar gain, expect all aspects at mid and lower elevations to see warming that will create wet snow on the surface of our snowpack.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
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 03/29/2019 at 7:12 AM.
USDA Forest Service
White Mountain National Forest