Avalanche Forecast for Sunday, December 16, 2018

This forecast was published 12/16/2018 at 7:05 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 12/16/2018 at midnight.


The Bottom Line

Areas of somewhat soft snow in the alpine, that skiers and riders will naturally be drawn to, are generally soft wind slab and are the same locations where it will be possible to trigger an avalanche today. There are a number of snow surfaces and layers to keep an eye on, and it’s a time to continue responsible travel in avalanche terrain. Bring beacon, shovel, and probe along with your brain and a good partner; travel one at a time, and evaluate snow and terrain carefully. Careful terrain selection today can be used to manage the primary avalanche problem today. All forecast areas have MODERATE avalanche danger today with exceptions being the Right side of Tuckerman Ravine and the Northern gullies in Huntington Ravine which are rated LOW.

2018-12-16 Printable PDF

Forecast Area

Mountain Weather

It’s currently a few degrees below freezing on the summit of Mt. Washington, with a temperature inversion keeping lower elevations colder this morning. It looks as though the inversion will lift and allow temperatures to rise to around the freezing mark in much of our terrain today, with cloud cover forecast to slowly increase through the day and into the night. The current N wind, under 20 mph on the summit, may increase slightly while shifting through E to SE as a weather system approaches. We should receive some new snow, though measurable accumulation is not expected before this avalanche forecast expires at midnight tonight. Snow totals by tomorrow night could be several inches or more.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Relatively soft areas of wind slab which formed late last week remain possible to human trigger and should be your primary avalanche concern today. Firmer, generally larger, and more stubborn wind slab also exists in our terrain and should be respected though are less likely to be human triggered. Both of these types of wind slabs can be found on the eastern half of the compass rose in alpine terrain. We’re on the cusp of temperatures and sun combining to warm these existing slabs and decreasing stability, so be suspect if you encounter snow that has been affected by warming.

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

The Presidential range currently holds a variable and somewhat complex snowpack. Areas of recently formed and relatively soft wind slab alternate with firmer wind slab that is generally older.The December 3rd melt freeze crust is also present at the surface along with a few areas of more recent sun crust. The softer wind slabs tend to be both more reactive and smaller, with some avalanche activity since late Friday, and the firmer wind slabs which are mostly older are more stubborn and generally larger. It’s worth noting that facet development around the December 3rd crust seems to be occurring. More developed and widespread facets have been observed at low elevation gullies in the Crawford Notch area, which may create a greater stability concern if they persist until a significant storm loads our low elevation terrain.

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
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
03/17/19
05:26
4 CM 3.7 MM 9%4CM218 CM-14.5 C-2.5 C-15.0 CBrokenNo 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
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 12/16/2018 at 7:05 AM.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest