Avalanche Forecast for Sunday, January 27, 2019

This forecast was published 01/27/2019 at 6:58 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 01/27/2019 at midnight.


The Bottom Line

Wind drifted snow exists on slopes in the lee of a west wind as well as beneath terrain features and sits on top of a robust crust. Incoming snow today will increase both the size and distribution of these wind slabs. A bit of uncertainty exists in the forecast snow totals, but if we receive the upper end of the forecast 2-4”, these areas of wind slab will become possible to trigger by a skier or climber in steep terrain, earning a MODERATE rating. The exception to this is the Northern Gullies in Huntington which have a LOW rating due to their aspect. Until the snow starts to accumulate, the current avalanche hazard may be overshadowed by the potential of long, sliding falls on the icy bed surface. If traveling in avalanche terrain today, a kit complete with climbing equipment for the morning and avalanche rescue gear for the afternoon would not go amiss.

Printable 2019-01-27

Forecast Area

Mountain Weather

Thursday’s rain transitioned immediately to snowfall, with around 5” of snow falling on the summit and 1.5” at Hermit Lake (3800’) between then and now. Prevailing westerly wind over this same time period has trended downward in speed. Low pressure racing across the region today will drag a warm front this morning followed by a cold front later this afternoon. Both frontal passages are bringing moisture, but the bulk of the forecast 2-4” of snow today will arrive with the cold front this afternoon into evening. Current wind from the south at 35 mph will increase through the morning to around 50 mph, possibly moving toward SW at times, before becoming west as the cold front passes. Another 2” of snow may fall tonight before skies clear tomorrow and temperatures fall below 0F.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slabs have formed from snow showers over the past few days on terrain in the lee of a west wind. These wind slabs are small in size and interspersed with areas of exposed melt-freeze crust. Snow that is likely still available for transport above ravine elevations, combined with the forecast 2-4” today, will continue to build these wind slabs. Today’s shift in wind and eventual increase in speed will push the likelihood of triggering one of these wind slabs toward possible, particularly if we receive the upper end of forecast snow totals.

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

Thursday’s rain event has eliminated concerns of weak layers deeper in our snowpack for now. The melt-freeze crust was supportable above treeline yesterday while places in the trees still offered opportunities to post hole. Snow that arrived late on Thursday fell on a wet snow surface, allowing it to bond well to the robust crust that now exists. The likely weak layer today will not be the interface between the crust and wind slab but a density change between layers above the crust. That being said, any fall today, whether caused by a slip and fall or triggering the wind slab, will have dire consequences due to the fast nature of the hard crust. Self-arresting on the bed surface that exists is unlikely; fall prevention is a much better bet for today, performed by equipment and terrain selection.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch.

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 01/27/2019 at 6:58 AM.

Helon Hoffer
USDA Forest Service
White Mountain National Forest