Avalanche Forecast for Sunday, January 6, 2019

This forecast was published 01/06/2019 at 7:28 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 01/06/2019 at midnight.


The Bottom Line

Avalanche danger will increase today as snowfall and wind create new wind slabs in our terrain. As snow is transported, the likelihood of human-triggered avalanches will rise along with the potential for natural avalanches driving our CONSIDERABLE rating for today’s avalanche problem. Exposed melt-freeze crusts and older unreactive wind slabs do exist, providing opportunities to avoid traveling through the avalanche problem, though bear in mind these are isolated and may be directly under significant loading taking place above.

2019-01-06 Printable

Forecast Area

Mountain Weather

Temperatures on the summit reached 31F yesterday with all elevations below going above freezing under cloudy skies. Westerly winds averaged 30 mph, though daylight hours saw speeds drop below 20 mph at times. Today will feel much more like typical early January as a cold front passes, with NW wind increasing from a current 50 mph to sustained 75 mph by dark. Temperatures will drop through the day to around 0F. Snow showers today may bring up to a total of 4” by midnight, with up to 2” by midday. Wind will diminish tomorrow with no snow expected until the early hours of Tuesday.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Prime wind loading speeds from the NW plus potentially more snow (2-4”) may combine to create touchy new wind slab in leeward locations as well as cross-loading on many slopes. Snowfall totals come with a degree of uncertainty today, though some snow leftover from Thursday’s storm remains available for transport above many start zones. Today’s new wind slab will form on soft older wind slab in many locations, increasing the amount of snow the could be entrained in an avalanche. Today’s ratings are based both on the potential to trigger an avalanche in snow that arrives today as well as the potential size that could be produced in our terrain.

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

Our terrain has a drastically different snowpack depending on aspect. Wind slab that formed late this past week can be found on the eastern half of the compass. This cohesive slab can mostly be found above a less cohesive layer, though has proven unwilling to propagate a crack. That being said, skiers in steep terrain found significant sluffing yesterday, leading us to believe an avalanche that starts small has the potential to entrain a large amount of snow. This soft snow will also be moved further downslope into lower start zones today. Slopes with westerly aspects have been scoured to rain crusts and hold very little, if any, avalanche danger. These rain crusts do provide the potential for long sliding falls with rock and tree-filled runouts below.

Ski tracks disappear through the choke of the Chute from skier-induced sluffing from above the top of the hourglass.

Variability in the fetch above Tuckerman Ravine. Wind slab exists on E and SE aspects of the summit cone, much of the Bigelow Lawn is scoured to December rain crust, and soft snow available for transport today lies on and just below the rollover of the Headwall.

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
03/22/19
05:20
Trace Trace NC213 CM-4.0 C3.0 C-4.0 COvercastSnowView
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

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 01/06/2019 at 7:28 AM.

Helon Hoffer
USDA Forest Service
White Mountain National Forest