Avalanche Forecast for Saturday, February 2, 2019

This forecast was published 02/02/2019 at 7:14 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 02/02/2019 at midnight.


The Bottom Line

Westerly wind since Wednesday’s snowstorm has created wind slabs that remain possible to human trigger. Today’s avalanche problem of stubborn wind slabs is low probability but high consequence, meaning that  complacency due to the lower likelihood of avalanches may lead you to travel in terrain which still could produce a large avalanche. Some scouring to a crust may allow options to avoid this avalanche problem, but it may be difficult to visually identify this crust today. Reduce your risk by reducing your time spent under or on steep areas of larger slab, especially where snow has accumulated beneath steeper terrain features. MODERATE avalanche danger exists for most of our forecast areas, with the Northern Gullies of Huntington Ravine the one exception with LOW avalanche danger.

2019-2-2_printable_pdf

Forecast Area

Mountain Weather

West wind slackened from 80 mph to the current 60 mph by yesterday afternoon while shifting WNW. Temperatures remained quite cold, with a high of -13F on the summit and highs below 0F at our snow plots which are just below 4000’ in elevation. Today will be warmer, with a forecast summit high of 2F. Summit wind should remain WNW and increase to 70 mph by this afternoon. Snow showers are likely to produce an inch or so of accumulation, predominantly falling this afternoon, but the notoriously tricky to predict upsloping affect may produce more snow by this afternoon or evening. No precipitation is forecast for tomorrow as temperatures rise to 20F on the summit and wind tapers to under 40 mph.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slabs formed through yesterday morning on consistently W wind following Wednesday’s storm. These slabs can be found on the eastern half of the compass rose, with the largest slabs in directly east facing terrain. Expect them to be stubborn to a human trigger and generally firm, with a few exceptions being softer in sheltered terrain. Additional snow today, which will be affected by WNW wind, could add volume to these slabs or develop smaller and more reactive slabs on the surface. Potentially small snow totals may minimize these new slabs. Terrain most exposed to wind will exhibit scouring to or near to the January 25th rain crust. These typical Presidential Range stubborn wind slabs aren’t likely to avalanche from a human trigger, but the possibility does remain and should certainly keep you from letting your guard down.

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

Field observations yesterday combined with the history of sustained 70-80 mph wind events lead us to believe that the relatively large wind slabs formed since Wednesday are generally hard and stubborn. The supportive nature of these hard slabs can offer substantial bridging strength, reducing the likelihood of a human triggered avalanche. That said, the slow bonding inherent to our current cold temperatures,the presence of an ice crust in the upper snowpack, and generally well developed slide paths with few anchors remaining are factors that help keep a relatively large avalanche a possibility today. Remember that these wind speeds also produce significant spatial variability, making it difficult to apply stability test results across terrain. Scouring has occurred in places and travelling on exposed crust may be an option to avoid the avalanche problem. Scouring in some upper avalanche start zones, like the Headwall of Tuckerman Ravine, has combined with sluffing to create the largest wind slabs relatively lower down in our avalanche paths. These combined sluff and wind slabs produced a number of natural avalanches since Wednesday, check out our observations page for more details.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. The annual MWV IceFest this weekend draws climbers from all over New England to the mountains this weekend. The White Mountain Avalanche Education Foundation will be at the event tonight and Frank will give a brief presentation about terrain management and avalanches in Huntington Ravine.

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
02/18/19
05:22
Trace Trace NC201 CM-14.5 C-9.0 C-16.5 COvercastSnow
02/17/19
05:24
Trace Trace Trace204 CM-16.5 C-9.5 C-16.5 CClearNo precipitation
02/16/19
05:22
13 CM 10.7 MM 12%13CM205 CM-10.0 C-2.0 C-10.0 COvercastNo precipitation
02/15/19
05:22
Trace 0.1 MM30CM195 CM-7.0 C-5.0 C-15.0 COvercastNo precipitation
02/14/19
05:24
11 CM 6.5 MM 10%NC196 CM-14.0 C-6.0 C-15.0 COvercastSnow

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
02/17/1914 F-3 F 0.00 in 0 in37 MPH74 MPH

310 (NW)

View
02/16/198 F-5 F .05 in .8 in52.4 MPH84 MPH

310 (NW)

02/15/1925 F7 F .37 in 2.7 in45.3 MPH84 MPH

240 (WSW)

02/14/1919 F-4 F .13 in 1.1 in56.2 MPH90 MPH

280 (W)

02/13/1916 F0 F .87 in 5.1 in46.3 MPH92 MPH

280 (W)

View
02/12/1912 F2 F .54 in 3.3 in37.5 MPH76 MPH

130 (SE)

02/11/196 F-9 F 0 in 0 in59.0 MPH86 MPH

330 (NNW)

02/10/19-4 F-13 F 0 in 0 in65.3 MPH101 MPH

290 (WNW)

02/09/19-7 F-14 F .01 in .2 in87.5 MPH148 MPH

280 (W)

02/08/1937 F-8 F .20 in .2 in71 MPH124 MPH

230 (SW)

02/07/1934 F22 F .04 in .2 in32.2 MPH56 MPH

250 (WSW)

02/06/1932 F17 F .23 in .4 in30.9 MPH68 MPH

330 (NNW)

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 02/02/2019 at 7:14 AM.

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