Avalanche Forecast for Thursday, December 6, 2018

This forecast was published 12/06/2018 at 7:06 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 12/06/2018 at midnight.


The Bottom Line

Today’s range-wide avalanche danger rating of LOW will depend upon the summits receiving the lower end of the one to three inches of snow during the daylight hours. Steep, higher elevation slopes with east through south aspects may develop wind slabs that are on the larger side of small if snow and wind loading exceed our current expectation of arrival later in the afternoon and evening. Stay vigilant for accumulating and blowing snow and change your route if you encounter “upside-down” snow with firmer snow over softer snow. Three inches of snow may not seem like much but if wind blows in the 50 mph range from the west, wind slabs one foot or more thick could result in east facing terrain.

2018-12-06 One Page Printable PDF

Forecast Area

Mountain Weather

Calm winds and fair skies yesterday allowed folks to enjoy the rare calm conditions around the Presidentials. The wind began to increase and shift to the northeast and north last night and is currently blowing in the 40 mph range from the northwest. An inch of new snow fell at Hermit Lake since yesterday afternoon. One to three inches more snow is forecast to fall today on the summits. This new snow and winds at a speed that is right for loading snow onto leeward slopes of a northwest wind is creating today’s avalanche problem. The high temperature on the summit will remain in the single digits.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slabs on steep, east and south facing ravine elevation slopes from recent or ongoing wind loading should be on your radar today. Reduced visibility due to summit fog will make identifying the newly formed wind slabs challenging. Avoid hollow sounding slabs of snow and be aware of who or what is above you on the slope. Avalanches are unlikely today unless you seek out areas of deeper, wind deposited snow.

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

About 5” of new snow has fallen since rain fell all the way to the summits. Some of this snow was very low density and easily transported. Yesterday, the soft wind slabs that resulted were stable in a few areas where skiers tested them in Tuckerman Ravine. These slabs were around boot-top depth on aspects that faced east and south. One skier commented that it was surprising to find areas of boot-top snow on a slope with a Low danger rating. A four hour period of blowing snow with winds from the north to northeast was reported overnight and likely refilled slopes with a southerly aspect. Lower elevations in Crawford Notch showed all the signs of a thaw with a 2” thick breakable crust over deep and sugary snow. The crust could break away at times on ice climbs and steep slopes. Steep open areas at all elevations are supportable more often than not on the rain crust, though that crust won’t be prominent at upper elevations that received the 5” new snow and wind loading. Some slopes still present a long-sliding fall risk due to the firm, refrozen crust.

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
04/18/19
05:15
0 CM 0.0 MM0CM185 CM2.5 C5.5 C-4.0 CClearNo precipitation
04/17/19
05:14
0 CM 0.0 MM0CM190 CM-4.5 C5.0 C-8.0 CClearNo precipitation
04/16/19
05:56
0 CM 6.3 MM0CM0 CM6.0 C8.0 C6.0 CObscuredGraupel and hail
04/15/19
05:21
0 CM 24.4 MM0CM193 CM1.0 C8.0 C1.0 COvercastRain
04/14/19
05:20
0 CM 0.0 MM0CM200 CM1.0 C9.0 C1.0 CClearNo precipitation

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
04/16/1916 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)

04/11/1924 F4 FTrace Trace 20.8 MPH77 MPH

300 (WNW)

View
View
04/10/1913 F7 F .11 in 1.1 in46.8 MPH72 MPH

300 (WNW)

04/09/1932 F12 F .14 in 1.9 in38.2 MPH72 MPH

290 (WNW)

04/08/1931 F12 F 0.52 in 3.3 in39 MPH82 MPH

270 (W)

04/07/1932 F18 F 0.04 in 0.2 in42 MPH68 MPH

290 (WNW)

04/06/1926 F18 F 0.26 in 1.5 in57.5 MPH87 MPH

290 (WNW)

04/05/1927 F-1 F 0.14 in 0.9 in41.3 MPH90 MPH

310 (NW)

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 12/06/2018 at 7:06 AM.

Frank Carus
USDA Forest Service
White Mountain National Forest