Avalanche Forecast for Monday, March 9, 2020
This information was published 03/09/2020 at 7:02 AM.
The Bottom Line
Warmth today will decrease snow stability. This will be greatest on steep slopes that see the most solar gain today. Avalanche danger will rise to MODERATE as cold, dry snow becomes wet and warm. We expect the overall size of possible avalanches to remain on the smaller side, but the widespread likelihood of triggering an avalanche today creates heightened avalanche conditions and demands users identify features of concern. Pay attention to slope aspect and how sloppy the snow gets underfoot today. With forecast temperatures well above freezing today, be on the lookout for icefall at mid and lower elevations.
Yesterday was clear and windy. Minor snow transport was observed in the morning. Temperatures stayed below freezing at all elevations. No new snow has fallen since Friday evening.
Today will be clear during the morning and gain warmth. All elevations will go above freezing. At 6am the summit is 23F with a forecast high of 35 mid-afternoon. A slight chance of rain exists as clouds develop later today. West wind will be 50-70mph, perhaps decreasing slightly midday.
Tomorrow, warm temperatures will continue after some upper elevations dip back below freezing tonight. Precipitation is forecast tomorrow with up to 2” of snow on the summit if rain doesn’t mix in. Mid and lower elevations will see more rain.
Primary Avalanche Problem – Wet Loose
Wet loose avalanches today are more likely to occur on very steep slopes that heat fast. This could be lower elevations that at 6am are already above freezing or mid-elevation slopes with a southerly aspect that will see significant solar gain. Watch for pinwheels and rollerballs as a sign that wet loose avalanches are becoming possible. While this sort of avalanche problem may not produce anything bigger than a D1 avalanche, these flows that act like wet cement have the potential to catch skiers or climbers and drag them over a cliff or ice bulge.
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
Existing wind slabs will warm today. As today will be the first warming for many of the wind slabs in avalanche terrain, expect a decrease in stability. This warming process will be driven both by ambient air temp (forecast 35F at 6288’ today) and by solar gain as skies will be clear. If you find snow getting wet and mushy, you’re in the midst of today’s warming wind slab. These wind slabs have proven to be unreactive and display good stability thanks to many observations form the public. Because of this good stability recently, it’s unlikely today’s decrease in stability or a even a wet loose avalanche could impact deeper layers; warming wind slabs today should remain shallow in depth, but could entrain enough snow to bury a person if a terrain trap comes into play. Consider the consequences even a small avalanche can have today.
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.
Today’s avalanche problems are surface problems. Digging in the snow today won’t be a waste of time as learning is great, but it won’t help you answer the question of “should we ski the slope?” The best notes to take today will be observations of what the snow is doing under your feet and how it changes as the day progresses. Snow that is becoming the consistency of a slushie from the Kwik-E-Mart is going to offer the highest chances of creating an avalanche today. As the day heats, nature will give you signs that the snow is becoming unstable. If you’re tempted to start throwing snowballs, be on the lookout for wet activity on steep slopes. Snow falling off trees and entraining snow as it rolls down the slope is a good precursor to wet activity. The sort of avalanche activity we expect to see today is manageable, but does require experience in heavy sluff management and should be practiced on slopes with limited terrain traps or consequential runouts.
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 03/09/2020 at 7:02 AM.
USDA Forest Service
White Mountain National Forest