Avalanche Forecast for Thursday, December 27, 2018

This forecast was published 12/27/2018 at 7:03 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 12/27/2018 at midnight.


The Bottom Line

Lingering pockets of wind slab exist scattered across the hard, refrozen surface snow in our steep terrain. The hard surface will require crampons, an ice axe and good climbing technique to avoid a slip which could quickly turn into a long, sliding fall. Ice climbs were damaged by the recent rain so be on the lookout for pressure building behind ice with the potential for rupturing.

2018-12-27 Printable Forecast PDF

Forecast Area

Mountain Weather

2cm of new snow fell at Hermit Lake with half an inch recorded on the summit of Mt. Washington during snow shower activity in the past 24 hours. Around 4.5” of snow has fallen on the summit in the past five days. Current temperature on the summit is -2F with wind from the NW at 56mph. Temperatures will warm to the teens on the summits through the day as wind subsides and shifts west at 30-45 mph, and even lower in the afternoon. The next round of precipitation arrives tonight and continues through tomorrow with 4-6” of snow falling overnight on increasing south west winds before a transition to sleet, freezing rain and finally rain by afternoon all the way to the higher summits.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slabs built over the past few days are likely to be stubborn but assess them before committing to steep slopes with newer snow. Even a small avalanche can have significant consequences in steep terrain, particularly with our currently icy surface conditions.

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

There has been no reported avalanche activity since the 3” of rain fell December 21-22 and “reset” our snowpack. New snow and mixed precipitation coming tonight and tomorrow will be arriving with building winds and increasingly dense snow before changing over to sleet and rain. The window of enough snow to slide on without avalanches due to building wind slab or wet slab danger seems tiny if it exists at all.

Additional Concerns

The Sherburne and Gulf of Slides ski trails have snow and ice coverage to Pinkham Notch. Heavy rain on December 21-22 did some damage and melted snow in some waterbars.

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 12/27/2018 at 7:03 AM.

Frank Carus
USDA Forest Service
White Mountain National Forest