Avalanche Forecast for Wednesday, December 26, 2018

This forecast was published 12/26/2018 at 6:57 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 12/26/2018 at midnight.


The Bottom Line

Isolated wind slabs exist on the steepest wind-sheltered areas on aspects facing away from a northwest wind. These smooth, pillowy looking areas are small and most likely stubborn to a human-trigger but are not entirely harmless due to the icy old snow that they are resting on. Fresh wind slabs may develop quickly this afternoon as wind speeds and the rate of snowfall increases. The hard and fast surface of rain-soaked and refrozen wind slabs in steep terrain create a risk as great as the wind slab avalanches. Crampons and an ice axe will be key safety tools for those braving the frigid temperatures and high winds today.

2018-12-26 Printable forecast

Forecast Area

Mountain Weather

No new snow fell in the mountains during the past 24 hours. We are starting the day at -6F with 55 mph NW winds, clear skies and good visibility. Cold conditions will continue today, with strong NW winds on the increase. Windspeeds will ultimately reach the 60-80 mph range later this afternoon as clouds thicken and lower. Another inch or two of snow is possible as upslope snow showers begin later today. Light, dry snow and high winds will create a recipe for wind transported snow and more wind slab development. Tomorrow will be slightly warmer, with diminishing winds and clear skies. The next chance for precipitation comes Thursday night and Friday which should start as snow but end with rain.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Assess the isolated pockets of wind slab on the steepest areas of wind sheltered slopes before you commit to walking or climbing on them. These smooth, pillowy looking areas are likely to be small but not entirely harmless due to the icy old snow that they are resting on. Wind slabs developing later this afternoon are likely to be more sensitive to triggering. Keep an eye on the rate of snowfall and snow blowing on the wind.

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

After an exceptionally snowy November, December seems particularly….un-snowy. Just 23.3” of snow has fallen this month, though if the 3” of rain had fallen as snow that total snowfall would be more than double, bringing us back in line with the 45.5” average for the month. That rain event undermined snow and ice, opened up streams and generally caused mayhem in the steep terrain. The now icy surface has set us up for some challenging times for skiers, and created either good cramponing or long sliding fall conditions, depending on whether you are a glass half-full or half-empty kind of person. With any luck, this next storm on Thursday will spare us much rain or at least deliver a snowy refresh before switching over.

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 12/26/2018 at 6:57 AM.

Frank Carus, Lead Snow Ranger
USDA Forest Service
White Mountain National Forest