Avalanche Forecast for Tuesday, December 25, 2018

This forecast was published 12/25/2018 at 7:20 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 12/25/2018 at midnight.


The Bottom Line

Avalanche danger today is confined to recently formed wind drifts, but the hard refrozen snow present in much of our terrain means that even a very small avalanche could cause a big fall. Watch for these areas of new and likely quite small wind slabs when route finding today, remembering that the LOW avalanche danger in all forecast areas does not mean no avalanche danger. Be equally or more mindful of the potential for high consequence long sliding falls on the hard and smooth refrozen snow. Consider fall consequence when choosing terrain, and travel with your solid crampon and ice axe skills this sunny Christmas day!

2018-12-25_Printable_PDF

Forecast Area

Mountain Weather

Modest overnight snowfall has been affected by NW wind recorded in the 50-70 mph range on the summit. This wind will continue though decrease slightly today. Hermit Lake and the Summit recorded 1.5” of snow, with Grey Knob coming in a little higher at 3 inches. Skies have cleared and should remain so through today. Temperatures will climb from the current -2F on the summit towards 10F. Tomorrow’s temperatures are forecast to be similar, with increasing clouds bringing a possible trace of snow as NW wind continues and increases through the day.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

New wind slabs that you’ll likely find in isolated pockets throughout the eastern half of the compass rose may be reactive to a human trigger. We expect these to be small in size, but highly variable conditions mean that a few larger pockets could also be found.  It should be possible to avoid this avalanche problem by staying on areas scoured to hard refrozen snow, but there is potential for constricted terrain features to minimize this avoidance option in narrow gullies.

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 low density snow we received last night will have been easily transported by the sustained NW wind, leaving pockets of new wind slab. A few small pockets of wind slab formed Saturday into Sunday also can be found. Consistently cold temperatures since the significant rain and warming event late last week have refrozen the rest of our snowpack into a solid and quite stable state. Avalanche concerns are limited to the isolated pockets of wind slab described in the avalanche problem. For the time being, the hard snow surface which provides great crampon purchase also makes long sliding falls of greater concern than avalanches in most of our terrain.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are mostly snow covered to Pinkham Notch, but expect to find areas melted out by the recent rain storm.

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
01/21/19
05:15
19 CM 26.6 MM 16% 32 CM  175 CM-20.5 C-7.0 C-24.0 COvercastNo precipitationView
01/20/19
05:20
13 CM 12.5 MM 11% NC CM  158 CM-15.5 C-12.0 C-17.5 COvercastSnowView
01/19/19
05:18
2 CM 0.7 MM 8% 2 CM  145 CM-16.0 C-10.0 C-16.0 CClearNo precipitation
01/18/19
05:18
0 CM 0 MM 0 CM  145 CM-14.5 C-13.0 C-20.0 CBrokenSnow
01/17/19
05:18
1 CM 1.4 MM 1 CM  147 CM-20.0 C-9.0 C-22.0 CClearNo precipitationView

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 12/25/2018 at 7:20 AM.

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