Avalanche Forecast for Sunday, December 30, 2018

This forecast was published 12/30/2018 at 7:15 AM.
A new forecast will be issued tomorrow.


This is an archived avalanche forecast and expired on 12/30/2018 at midnight.

The Bottom Line

Yesterday’s snow and wind deposited wind slabs in isolated areas and behind or below specific terrain features. Wind slab should be easy to identify and avoid in contrast  to the refrozen scoured surfaces that exist in many locations. Terrain which contains these wind slabs has MODERATE avalanche danger. Wind scoured areas of icy, hard snow create conditions prime for long, sliding falls. Evaluate snow and terrain carefully to identify and avoid these hazards. Equipment to perform avalanche rescue as well as crampons and an ice axe should be included in today’s kit.

2018-12-30 Printable PDF

Forecast Area

Avalanche Safety Information Study

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Mountain Weather

Friday morning brought two inches of snow to our highest elevations that was followed by a half inch of rain in the afternoon. Lower elevations saw the changeover to rain sooner, with higher rainfalls totals and less snow. After an overnight lull, precipitation resumed Saturday morning as temperatures dropped. The summits received all snow (2.1”) with a trace at Gray Knob and at Hermit Lake. At 6am this morning, skies are overcast, north wind is blowing 20 mph and the air temperature is 6F. Today, temperatures will climb to 10F with wind shifting to the north and increasing to 30-45 mph, and some mid and high level clouds passing the region. Monday will start similar to today, though New Year’s Eve celebrations will involve significant snowfall on the summits with rain likely at lower elevations.

Primary Avalanche Problem – Wind Slab

Wind Slab




High wind speeds transported the two inches of snow that fell on the summit yesterday into areas of wind slab in lee locations of a NW wind. This wind slab is likely stubborn to human triggers, though specific locations may harbor wind slab close to a foot thick. You may be able to avoid today’s avalanche problem by staying on scoured surfaces, but some pinch points of gullies or narrow slopes may hold wall to wall wind slab.

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

Two inches of snow fell at higher elevations as our snowpack was refreezing on Saturday. This snow arrived on NW wind around 80mph. Wind of this magnitude likely transported most available snow onto slopes in the lee of NW or into the trees. Traveling surfaces today will be  areas of wind slab mixed with wind scoured crusts. Remember that hard wind slabs that are present today may not release or fail in response to the first skier or rider. Traveling one at a time across suspect slopes will be key to safe travel today.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. If you’re in the greater Boston area in a week (January 8) be sure to head to Arc’teryx Boston for evening avalanche awareness presentation with Ryan Matz.

Snow Plot Information

Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
0 CMTrace 0CM0 CM8.0 C11.0 C0.5 CBrokenNo precipitation
0 CM 0.0 MM0CM0 CM7.5 C7.5 C1.0 CScatteredNo precipitation
0 CM 22.3 MM0CM0 CM1.5 C4.0 C0.0 COvercastNo precipitation
0 CM 0.0 MM0CM0 CM0.5 C11.0 C0.5 CClearNo precipitation
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 12/30/2018 at 7:15 AM.

Helon Hoffer
USDA Forest Service
White Mountain National Forest