Avalanche Forecast for Sunday, December 23, 2018

This forecast was published 12/23/2018 at 7:08 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 12/23/2018 at midnight.


The Bottom Line

New snow that fell at the tail end of the rain event, combined with extreme winds, has formed isolated areas of wind slab that should be small and easy to avoid by staying on wind scoured slopes. All elevations and aspects have LOW avalanche danger today. In all locations, long, sliding falls will create equal, if not greater, hazard for the day. Ice dams and undermined snow will add to the list of objective hazards that are present in the range today.

2018-12-23 Printable PDF

Forecast Area

Mountain Weather

The rain event over the past few days introduced close to 3” of rain to our snowpack. Temperatures fell below freezing late Saturday morning, continuing to drop to a current 1F on the summit. Before precipitation shut off, 2.1” of snow fell on the summit, about ¾” at Grey Knob, and a trace at Hermit Lake. This snow arrived on 40 mph west winds that shifted WNW and increased to 80+ mph for the remainder of the day. High pressure across the region today will create clear skies, decreasing wind speeds from NW 74 mph at 6am to around 30 mph by dark, and temperatures in the teens F. Clouds will develop late in the day with a chance of snow, though accumulations should be minimal. The next round of high pressure will move in Monday afternoon, setting up a dry pattern for the holiday week.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slab that formed yesterday afternoon is likely small, isolated, and stubborn to a trigger by skiers and climbers due to high wind speeds. The largest and thickest areas of wind slab can be found in the direct lee of WNW wind with the largest fetch, such as low in the Headwall area of Tuckerman. These wind slabs should be easily discernible from other refrozen, scoured surfaces.

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

Following a snowy November and cold start to December, the inevitable reset button was hit for our snowpack this past week. Three inches of rain with warm temperatures saturated the upper part of our snowpack and was followed by plummeting temperatures, creating a hard and fast sliding surface. While the avalanche problem exists today, it is isolated in nature and other objective hazards deserve as much respect. Long, sliding falls will be possible on any slope but flat surfaces: use crampons and an ice axe properly. Ice dams will form when a flash freeze follows rain events. Climbers should be particularly aware of this on all aspects and elevations. Holes in the snow due to undermining were visible yesterday in many gullies and are a good indication of thin spots in the snowpack.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch, though expect ice, the occasional rock, and open waterbars to add to the challenge.

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 12/23/2018 at 7:08 AM.

Helon Hoffer
USDA Forest Service
White Mountain National Forest