Avalanche Forecast for Friday, December 7, 2018

This forecast was published 12/07/2018 at 7:07 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 12/07/2018 at midnight.


The Bottom Line

New snow combined with NW wind today will continue to create wind slab at higher elevations. This loading will likely be most prevalent in the lee of ridges and terrain features. Look for cross-loading on south and north facing aspects. Do not be deceived by the lack of snow in runouts as you approach a gully; many start zones are well filled in and becoming connected in our bigger avalanche paths. With whiteout conditions possible today, you may have trouble seeing today’s avalanche problem until you are in it. Today’s rating of MODERATE in the Central area of Huntington, the Headwall of Tuckerman, and the Presidential Range is due to the size of wind slab being built and the possibility of a person being able to trigger this problem. Other forecast areas (Northern and Southern Gullies in Huntington, Right Side, Left Side and Boott Spur in Tuckerman) have a LOW rating due to their aspect and lesser wind slab development.

2018-12-07 Printable

Forecast Area

Mountain Weather

As of 5:30am this morning, 11cm of 6% snow fell at Hermit Lake and 7cm at Gray Knob in the prior 24 hours. This arrived on a west wind that blew steadily around 50mph for the day. Prior to the arrival of the cold front heading our way later today, another 1-3” of snow may fall on NW wind around 40mph, increasing to 60mph in the afternoon. Temperatures will fall later in the day, with higher elevations seeing temperatures below 0F this evening.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slab is forming in avalanche start zones and will push down to mid-elevations as the day progresses. New snow as well as wind loading are both red flags for avalanche hazard. Steady wind from the NW today, combined with light density snow, should move most snow from the west side of the range to the east. Scouring may take place in areas with a westerly aspect, but unless the melt/freeze crust is visible on the surface, there is likely wind slab that formed earlier this week still present that will need to be assessed.

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

A robust melt-freeze crust formed after the rain this past Sunday. We’ve seen 6.2” of snow fall on the summit since with varied wind speeds and direction. Wind slab that built Monday and Tuesday seems largely firm, though varied in thickness. Loading that took place yesterday into today is the primary driver for avalanche hazard, though an avalanche occurring in this layer could easily entrain snow from earlier in the week to create a larger avalanche. Safe travel today will require careful snowpack evaluation and the knowledge of when it is time to turn around.

Additional Concerns

Cold temperatures, blowing snow, and high winds will create true mid-winter conditions in the mountains today. Be prepared with extra layers and keep an eye out on your partner for frostbite.

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
02/18/19
05:22
Trace Trace NC201 CM-14.5 C-9.0 C-16.5 COvercastSnow
02/17/19
05:24
Trace Trace Trace204 CM-16.5 C-9.5 C-16.5 CClearNo precipitation
02/16/19
05:22
13 CM 10.7 MM 12%13CM205 CM-10.0 C-2.0 C-10.0 COvercastNo precipitation
02/15/19
05:22
Trace 0.1 MM30CM195 CM-7.0 C-5.0 C-15.0 COvercastNo precipitation
02/14/19
05:24
11 CM 6.5 MM 10%NC196 CM-14.0 C-6.0 C-15.0 COvercastSnow

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
02/17/1914 F-3 F 0.00 in 0 in37 MPH74 MPH

310 (NW)

View
02/16/198 F-5 F .05 in .8 in52.4 MPH84 MPH

310 (NW)

02/15/1925 F7 F .37 in 2.7 in45.3 MPH84 MPH

240 (WSW)

02/14/1919 F-4 F .13 in 1.1 in56.2 MPH90 MPH

280 (W)

02/13/1916 F0 F .87 in 5.1 in46.3 MPH92 MPH

280 (W)

View
02/12/1912 F2 F .54 in 3.3 in37.5 MPH76 MPH

130 (SE)

02/11/196 F-9 F 0 in 0 in59.0 MPH86 MPH

330 (NNW)

02/10/19-4 F-13 F 0 in 0 in65.3 MPH101 MPH

290 (WNW)

02/09/19-7 F-14 F .01 in .2 in87.5 MPH148 MPH

280 (W)

02/08/1937 F-8 F .20 in .2 in71 MPH124 MPH

230 (SW)

02/07/1934 F22 F .04 in .2 in32.2 MPH56 MPH

250 (WSW)

02/06/1932 F17 F .23 in .4 in30.9 MPH68 MPH

330 (NNW)

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 12/07/2018 at 7:07 AM.

Helon Hoffer
USDA Forest Service
White Mountain National Forest