Avalanche Forecast for Friday, March 20, 2020
This information was published 03/20/2020 at 7:12 AM.
The Bottom Line
Snow will get wet today. As the day progresses with warm temperatures continuing and eventually rain, wet avalanches will become possible to trigger. When traveling through terrain, monitor snow underfoot for how deep the snow is getting wet. Boot top wet snow is a sign stability has decreased. MODERATE avalanche danger exists today as wet snow avalanches become possible. In addition, watch for falling ice today as temperatures work to delaminate ice from rock.
Yesterday, a trace of snowfall on 30mph wind from the south brought our snow total since last week’s warm-up to 3”. Temperatures yesterday started cold and ended the day above freezing.
Today at 6am, temperatures are:
- Mount Washington (6288’): 35F
- Gray Knob (4370’): 42F
- Hermit Lake (3800’): 45F
Temperatures will maintain these numbers through daylight hours, possibly increasing. Wind at 6am is from the SW at 45mph and will shift to the W and increase toward 100mph by dark. Rain is forecast today with up to a half inch of water by midnight. Mid-afternoon has the greatest chance of heavy rain.
Tomorrow will start cloudy and cold, becoming clear. Temperatures on the summits should be close to the single digits by dawn. Wind from the NW will start the day at 60-80mph and decrease slightly. A slight chance of morning snow flurries exists.
Primary Avalanche Problem – Wet Slab
Wet slab avalanches may be triggered in any place that contained soft snow yesterday (our recent wind slab problem). Largely, the size should be small, but possible to trigger. You may be able to produce an avalanche capable of burying a person in due east facing terrain such as the Headwall in Tuckerman or one of the numbered gullies in Gulf of Slides. The fact that these wetting slabs sit on a stout ice crust exacerbates today’s avalanche problem. This crust may act as a barrier for melt, becoming the layer that gets lubricated with a slab of wetting snow sitting on top. Watch for mushy snow or heavy rain as an indicator that the danger of wet slabs is increasing.
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.
Secondary Avalanche Problem – Wet Loose
Wet loose avalanches are possible due to above freezing air temperatures that have warmed the snow surface. These “sluff” avalanches should be small and localized to the steepest terrain. Watch for pinwheels or rollerballs as indicators that the snow surface is wetting and wet loose avalanches are trending. These most often cause harm by entraining your skis and dragging 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.
Spring skiing is all about timing. Today and tomorrow will be no different, it’s just that the window of timing right now is days, not hours. Today will be unpleasant outside thanks to wetting snow from warmth and rain, not to mention the forecast wind today. Tonight, temperatures will plummet, creating an alpine skating rink tomorrow. Neither day sounds great for getting that elusive taste of the outdoors we all crave. Look for the forecast, plan ahead, and be sure to match your outdoor expectations to the reality of mountain weather.
The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.
The Lion Head Winter Route remains the easiest route to the summit from Pinkham Notch but requires an ice axe, crampons (not just micro-spikes) and possibly a rope. This is a mountaineering route and requires solid skills for a safe, timely ascent.
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 03/20/2020 at 7:12 AM.
USDA Forest Service
White Mountain National Forest