Avalanche Forecast for Saturday, February 16, 2019

This forecast was published 02/16/2019 at 7:03 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 02/16/2019 at midnight.


The Bottom Line

New wind slabs that you could trigger on skis or on foot can be found on many aspects today. Shifting winds have created these widespread wind slabs in our middle and upper elevation terrain.The new wind slabs vary in size and sensitivity to triggering due to these changes in wind speed and direction, with large and reactive slabs likely in specific areas.  If you travel in avalanche terrain today, be ready to make continual assessments of the upper snowpack to guide your travel decisions. All forecast areas have CONSIDERABLE avalanche danger. Natural avalanches remain possible in areas that receive further wind loading today. Low elevations which received rain and a refreeze last night are the exception and lack today’s avalanche problem.

2019-2-16_printable_pdf

Forecast Area

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Mountain Weather

Snow yesterday totaled 5” at our snow plots. An afternoon changeover to rain occurred below about 3500’ in elevation where temperatures were above freezing. Southerly wind held between 40 and 50 mph with stronger gusts until a shift to W wind yesterday evening. Several hours of W wind near 60 mph ultimately diminished to the current 45 mph, which is forecast to shift NW and increase this afternoon. Temperatures are currently below freezing throughout our terrain and should remain so through the day, with a trace to 1” of snow forecast. Mostly clear skies, no precipitation, and decreasing wind are forecast for tomorrow.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

South wind yesterday shifted west overnight, transporting the 5” of new snow and building wind slabs on a wide range of aspects. The wind will shift again to the NW and move more snow on the ground into avalanche starting zones. These wind shifts make wind slab the primary avalanche problem on all but SW and W aspects. Be on the lookout for soft and reactive wind slabs on most middle and upper elevation aspects with a fair amount of spatial variability due to these shifting winds. Layers formed earlier this week beneath the new wind slab could be pulled into moving avalanche debris and contribute to the size of a slide 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.

Snowpack and Avalanche Discussion

Five inches of new snow yesterday brings our total since Wednesday to nearly 20” for middle and upper elevations. This snow was affected by alternating periods of strong westerly and southerly wind, both in the past 24 hours and in the days prior. The resulting layers of wind slabs forming from this varied wind direction lie on a hard and slick rain crust, with some areas scoured to the crust. We expect slabs formed prior to yesterday to be stubborn though potentially able to contribute to size of an avalanche today, with slabs formed since yesterday being reactive to a human trigger. Low elevations are a different story, with rain and a subsequent refreeze last night.

Additional Concerns

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

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
05/31/19
05:20
0 CMTrace 0CM0 CM8.0 C11.0 C0.5 CBrokenNo precipitation
05/30/19
05:25
0 CM 0.0 MM0CM0 CM7.5 C7.5 C1.0 CScatteredNo precipitation
05/29/19
05:25
0 CM 22.3 MM0CM0 CM1.5 C4.0 C0.0 COvercastNo precipitation
05/28/19
05:25
0 CM 0.0 MM0CM0 CM0.5 C11.0 C0.5 CClearNo precipitation
05/27/19
05:15
0 CM 0.0 MM0CM10 CM8.0 C15.5 C8.0 CClearNo precipitation

Avalanche Log and Summit Weather

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
05/30/1946 F36 F 0 in 0 in27.9 MPH55 MPH

290 (WNW)

05/29/1947 F33 F 0 in 0 in20 MPH48 MPH

290 (WNW)

05/28/1934 F28 F .71 in 3.7 in20 MPH48 MPH

290 (WNW)

05/27/1940 F27 FTrace 0 in38.9 MPH68 MPH

300 (WNW)

05/26/1948 F39 F .77 in 0 in48.7 MPH75 MPH

290 (WNW)

05/25/1947 F31 F .42 in 0 in17.7 MPH63 MPH

240 (WSW)

05/24/1942 F32 F .66 in 0 in44.8 MPH105 MPH

05/23/1944 F30 F .16 in 0 in26.8 MPH71 MPH

270 (W)

05/22/1934 F21 F 0 in 0 in36.2 MPH115 MPH

330 (NNW)

05/21/1934 F23 F .57 in 1.9 in73 MPH135 MPH

330 (NNW)

05/20/1951 F33 F 0.57 in 0.0 in48 MPH82 MPH

250 (WSW)

05/19/1951 F34 F .6 in 0 in34.2 MPH66 MPH

250 (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 02/16/2019 at 7:03 AM.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest