Avalanche Forecast for Sunday, February 17, 2019

This forecast was published 02/17/2019 at 7:07 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 02/17/2019 at midnight.


The Bottom Line

It is possible for skiers and climbers to trigger a large avalanche today. Wind slabs that exist on the eastern half of the compass have a good deal of variability in their hardness. A double-edged sword exists in avalanche terrain with avalanche paths offering the less likely chance of producing a large avalanche while sheltered areas or treed slopes with softer snow give an increased likelihood of producing smaller avalanches. All areas have MODERATE avalanche danger due to the the potential of initiating a slide today as well as the possibility of producing a destructive avalanche. Terrain with a southern aspect, such as the Northern Gullies in Huntington, likely contains less developed wind slab and may offer more opportunities for safe travel. Good terrain management will provide ample opportunities for quality skiing and climbing.

Printable 2019-02-17

Forecast Area

Mountain Weather

Wind speed increased through the day yesterday with a shift to the NW. Steady speeds close to 70 mph were recorded late in the evening after starting the day in the 40 mph range. About 1” of snow fell at upper elevations. Today will be a pleasant mid-winter day with summit temperatures rising to 10F with wind from the NW becoming W and dropping from the current 60 mph to the 10-20 mph range by mid-afternoon. No snow is forecast today, though developing clouds this afternoon mark the incoming low pressure system that will bring steady but light snowfall tomorrow.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slabs that vary in hardness, from soft through hard, can now be found on a variety of aspects on the eastern half of the compass at middle and upper elevations. While overnight wind from the NW transported the inch that fell Saturday, it has also increased bridging strength, likely creating stubborn wind slab on exposed slopes like those in typical avalanche paths. Sheltered areas that are protected from high wind speeds contain softer wind slab that provide a more likely place to initiate a crack. While treed slopes may provide anchoring early in the season, today they may lure skiers onto the more reactive areas of today’s avalanche problem.

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

Our upper snowpack at mid and high elevations consists of layered wind slab resting on top of a crust that developed over a week ago. Field observations yesterday in Huntington and Tuckerman found a reactive surface wind slab in wind sheltered areas on top of a more stubborn layer of wind slab below. This all sits on top of a hard bed surface. Natural avalanche activity on NE aspects, that occurred this past Wednesday, indicates the possibility of a slide entraining all snow above the crust and producing a large avalanche. Lower elevations saw a brief period of rain on Friday, creating a breakable crust on the surface. While temperatures and cloud cover will negate warming above 3500’, the effect of warming down low may weaken the crust and weaken any slabs that may exist in steep terrain. Bright and direct sun on steep slopes and in wind protected areas would be the red flag to watch for.

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
03/22/19
05:20
Trace Trace NC213 CM-4.0 C3.0 C-4.0 COvercastSnowView
03/21/19
05:23
0 CM 0 MM0CM213 CM-1.5 C0.0 C-11.5 COvercastNo precipitation
03/20/19
05:28
0 CM 0 MM0CM214 CM-11.0 C-4.5 C-14.0 CClearNo precipitation
03/19/19
05:25
0 CM 0.0 MMNC215 CM-13.0 C-9.5 C-15.0 CFewNo precipitation
03/18/19
05:20
Trace 0.1 MMNC216 CM-15.5 C-13.0 C-15.5 CBrokenSnowView

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
03/20/1917 F1 F 0.0 in 0.0 in32 MPH58 MPH

270 (W)

03/19/194 F-4 FTrace Trace 43.4 MPH63 MPH

300 (WNW)

03/18/193 F-6 F 0.03 in 0 in52.1 MPH82 MPH

280 (W)

03/17/192 F-6 F 0.07 in .5 in61.5 MPH110 MPH

270 (W)

03/16/1925 F2 F 0.24 in 2.3 in67.5 MPH97 MPH

280 (W)

03/15/1941 F25 F 0.04 inTrace 54 MPH105 MPH

250 (WSW)

03/14/1940 F17 F Trace in Trace in27.7 MPH75 MPH

200 (SSW)

View
03/13/1924 F11 F .07 in .8 in29 MPH52 MPH

290 (WNW)

03/12/1911 F-1 F 0.14 in 1.9 in65 MPH104 MPH

280 (W)

03/11/1917 F6 F 0.35 in 4.4 in77 MPH114 MPH

280 (W)

03/10/1925 F4 F .35 in 3.7 in47.2 MPH94 MPH

150 (SSE)

View
03/09/1919 F0 F 0 in 0 in36.1 MPH70 MPH

290 (WNW)

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 02/17/2019 at 7:07 AM.

Helon Hoffer
USDA Forest Service
White Mountain National Forest