Avalanche Forecast for Friday, December 28, 2018

This forecast was published 12/28/2018 at 7:18 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 12/28/2018 at midnight.


The Bottom Line

Expect freshly forming wind slabs to be touchy to human triggers today. As new snow and wind drifts accumulate through the morning, natural avalanches will become likely, and may become more likely as snow turns to sleet and rain this afternoon. Avalanche danger may rise to CONSIDERABLE today in all mid and upper elevation forecast areas not facing directly southwest.

You can avoid these avalanches by staying on low angle or lower elevation terrain that does not have deep new snow or wind drifted snow. Travelling in longer avalanche paths will expose you to the risk of natural avalanches from above. Gusty and erratic wind that loads slopes with more snow could trigger these avalanches unexpectedly.

 

Forecast Area

Mountain Weather

Light snow began falling around 2am this morning and has picked up in intensity with sleet mixing in already, despite the ground level air temperature of 7F. Snow will continue through the morning on westerly then southwesterly wind around 60 mph. So far this morning, wind has been gusty and a bit erratic. Sleet will likely continue to mix in this morning, adding weight to the forming wind slabs, before a change over to freezing rain and rain later in the day. Precipitation will switch back to snow tonight with upslope snow showers delivering another couple of inches tomorrow.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Small to medium sized wind slab avalanches will be able gather enough snow to be dangerous, particularly considering the icy bed surface beneath. These wind slabs will grow increasingly unstable through the day as new mixed precipitation types falling on the snow adds stress to the weak snow near the icy bed surface.

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

Air and upper snowpack temperature recordings this morning are not favorable for new snow to bond to the existing, icy snow surface. This hard rain crust is widespread through our terrain and was the result of the 3” rain event on December 21-22. Despite losing almost 25cm of snow during that event, our avalanche paths are still well developed but with rocks, boulders, and ice cliffs now showing again. Given the glazed over snowpack and cold temperatures associated with this morning’s new snow, it would be wise to view the exposed boulders, bushes and cliffs in our avalanche paths as potential obstacles and not as anchors. Today’s avalanche problem is more of an angry badger backed into a corner than a burly grizzly bear.

Additional Concerns

The Sherburne and Gulf of Slides ski trails have patches or water ice and some recently exposed rocks mixed with the refrozen rain crust. New snow will obscure these obstacles.

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 12/28/2018 at 7:18 AM.

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