Avalanche Forecast for Wednesday, March 20, 2019

This forecast was published 03/20/2019 at 7:10 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 03/20/2019 at midnight.


The Bottom Line

Wind slabs formed over the weekend continue to strengthen under clear bluebird weather. Generally stable conditions are found at all elevations, though unstable pockets may exist in steep east facing terrain where the slabs will be the thickest. Under clear skies today, you’ll be able to easily see large expanses of bright, white but generally thin wind slab in the Headwall of Tuckerman Ravine and higher in the gullies of the Gulf of Slides. Sunny skies and slightly warmer temperatures may soften south facing slopes in the ravines enough for some good skiing – maybe.

For those seeking turns on sun softened snow, be mindful of the long sliding fall hazard on our largely refrozen hard snowpack. A thin edgeable layer of soft snow can result in a dangerous long sliding fall in steep terrain, and sun softened snow will refreeze quickly again with overhead clouds or a moving shade line. Crampons, an ice axe and your ability to accurately assess the chances for successful self-arrest are required for traveling on snow slopes today. All forecast areas have LOW avalanche danger.

2019-3-20_printable_pdf

Forecast Area

Avalanche Safety Information Study

Please contribute to the effort to improve backcountry avalanche forecasts! Researchers in Canada devised a study to better understand how we communicate the avalanche risk, and we need your help. Please fill out this survey. It will take a few minutes, but it will help us as we work on new ways to give you the most important avalanche information.

Mountain Weather

Yesterday, blue skies accompanied by the sun traversing high overhead suggests spring, however a 45 mph WNW wind and summit high temperature of 4F reminded us the mountains are still locked in winter mode. Today, we start the day under clear skies with W wind shifting to the SW at 30-35 mph this afternoon. Once the wind shifts, clouds may fill in overhead as warmer air moves in, pushing the summit high temperature into the mid teens F. SW wind will continue into tomorrow bringing slightly warmer temperatures, increasing clouds and a chance of snow.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slabs formed from three inches of snow over the weekend have had time to settle and are likely unreactive to a human trigger. You’ll find the largest, most continuous slabs in steep east facing terrain at mid elevation with the largest fetch, including the Headwall of Tuckerman Ravine and the gullies in the Gulf of Slides. In other areas, you’ll find these slabs to be more isolated pockets intermixed with terrain scoured to the refrozen surface. On the west side of the range, you’ll find much more scoured, frozen bed surface but don’t rule out the chance to find isolated pockets of wind slab. At lower and mid elevations, southern aspects may warm enough to soften the snow surface, but we don’t expect this to result in any instabilities.

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.

Snowpack and Avalanche Discussion

The depth of our stability concerns are limited to wind slabs that sit on top of the frozen crust resulting from the unseasonably warm weather last week followed by re-freezing on Saturday.  See 3/14 – 3/16 at https://mountwashingtonavalanchecenter.org/weather-avalanche-log/

Digging below this frozen crust you’ll find some a layered snowpack structure including dry soft snow, and even faceted weak layers, however due to the bridging power of this frozen crust it’s unlikely a human will trigger anything below, at least not until a prolonged rain event. This crust also presents a long sliding fall hazard. Typically a quick unexpected stumble, or very thin slab gives way, and turns into a rapidly accelerating slide for life downhill. Self arrest skills are often ineffective in stopping a sliding fall even in terrain that’s generally considered low angle like those on the approaches to climbs in Huntington Ravine.

Additional Concerns

Long sliding fall accidents outnumber avalanche accidents in the Presidential Range.

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
04/24/19
05:20
0 CM 1.7 MM0CM146 CM4.5 C7.0 C2.0 COvercastNo precipitation
04/23/19
05:22
0 CM 10.4 MM0CM152 CM3.0 C12.0 C1.0 COvercastRain
04/22/19
05:20
0 CM 0.0 MM0CM156 CM1.0 C10.0 C1.0 CFewNo precipitation
04/21/19
05:15
0 CM 28.0 MM0CM160 CM6.5 C11.0 C6.5 CBrokenNo precipitation
04/20/19
05:15
0 CM 16.5 MM0CM175 CM9.5 C12.0 C6.5 COvercastRain

Avalanche Log and Summit Weather

Daily Observations


Thank you Mount Washington Observatory for providing daily weather data from the summit of Mount Washington.

DateMax TempMin TempTotal (SWE)24H Snow & IceWind AvgWind Fastest MileFastest Mile DirAvalanche Activity
04/23/1946 F33 F .18 in 0.0 in25.8 MPH60 MPH

240 (WSW)

04/22/1942 F33 F .15 in 0.0 in18.1 MPH54 MPH

50 (NE)

04/21/1945 F36 F 0.21 in 0 in23.8 MPH66 MPH

170 (S)

04/20/1949 F43 F 1.11 in 0 in42.6 MPH96 MPH

240 (WSW)

04/19/1947 F41 F 0.23 in 0 in46 MPH95 MPH

240 (WSW)

04/18/1942 F18 F .23 in .2 in39.4 MPH98 MPH

240 (WSW)

04/17/1925 F15 F 0 in 0 in28.8 MPH82 MPH

330 (NNW)

04/16/1916 F12 F .28 in 1.5 in82.2 MPH142 MPH

290 (WNW)

04/15/1945 F12 F .97 in 1.6 in55.6 MPH133 MPH

290 (WNW)

04/14/1945 F24 F 0.22 in 0 in53 MPH85 MPH

290 (WNW)

04/13/1941 F28 F 0.09 in 0 in55.8 MPH86 MPH

280 (W)

04/12/1941 F20 F 0.15 in 0.0 in47 MPH106 MPH

240 (WSW)

Please Remember:

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 03/20/2019 at 7:10 AM.

Jeff Fongemie, Snow Ranger
USDA Forest Service
White Mountain National Forest