Avalanche Forecast for Monday, February 24, 2020
This information was published 02/24/2020 at 7:12 AM.
The Bottom Line
Cold snow that warms today is driving an decrease of stability. Slopes that see the most direct sun today (SE-SW) will see that amplified in comparison to other aspects. Aspects that have wet snow developing today will increase to MODERATE avalanche danger. Areas of snow that stay cold and dry today will offer generally safe avalanche conditions and provide safer travel for those looking to recreate. Please remember that you should always carry avalanche rescue gear and discuss travel techniques with your group to determine how you will manage the slope you plan to travel on.
Yesterday was dominated by sunshine and warming temperatures. Wind was from the west and hovered around 30mph for daylight hours. Highs from around the Presidential Range are as follows:
- Mt Washington summit (6288’): 24F
- Hermit Lake (E aspect below Tuckerman 3800’): 24F
- Gray Knob (W aspect on shoulder of Mt Adams 4370’): 34F
- Sluice Bowl (SW aspect 4800’ in Tuckerman): 35F
Today’s temperatures should be a repeat of yesterday with highs on the summit forecast in the upper 20sF. More moisture in the air early in the day and in the afternoon may create clouds or even periods of higher summits fog. Wind will again be from the west, though stronger, with speeds closer to 50mph in the morning before decreasing later in the afternoon. No precipitation is forecast.
Tomorrow, wind will calm with a chance of up to 1” of snow flurries. Continued warm temperatures will likely produce mixed precip or rain at lower elevations, though amounts are forecast to be minimal. Looking ahead, there’s significant snow forecast for Thursday.
Primary Avalanche Problem – Wind Slab
Rapid warming is a Red Flag in the avalanche world that indicates increasing instability. Wind slabs that exist currently in avalanche terrain will go through their second day of warming today. These slabs were firm and have proven unreactive as cold wind slabs. However, warming will destabilize the slab itself, perhaps moving the sensitivity of these slabs from away from unreactive. The greatest concern for these warming wind slabs today will be on the south half of the compass and places where the wind slab is thin. As you move around terrain today, track the thickness of the slab with your ski pole and the degree of warming by tracking how wet the snow is getting and how deep. If you start sinking in with your skis or boots to wet snow, recognize the slab has lost a lot of strength and stability is decreasing.
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.
Secondary Avalanche Problem – Wet Loose
Wet Loose avalanches are possible today as the sun and air temp increases the water content of snow due to melting. These will likely be small in size and are manageable by timing what aspect you travel on during the course of the day. These are more likely in steeper terrain and are most harmful if this snow that acts like uncured cement pulls you over a cliff or into a terrain trap.
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.
Today’s warming wind slab is hard to forecast. It’s driven by a warming process that on the surface looks like a wet avalanche issue, but the debris from a slab avalanche today would be dry snow. Air temperature will hover around the freezing mark for mid and upper elevations today driving some of the warming; south facing slopes will also see solar gain that will amplify this warming while east facing slopes will see much less of this destabilizing due to solar gain. Yesterday, the greatest warming observed in the field indicated snow was wetting almost 10cm deep. This was on a SW aspect mid-afternoon at 4800’ (Sluice Bowl). Our lower elevation band likely saw warmth penetrate further. Some uncertainty exists with today’s likelihood of triggering, though we think the combination of sun, air temp, and cloud cover will allow warming to penetrate further into the snowpack than yesterday. This depth would be something that I would track closely while moving around the field today to help identify aspects of concern.
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 02/24/2020 at 7:12 AM.
USDA Forest Service
White Mountain National Forest