Avalanche Forecast for Monday, January 21, 2019

This forecast was published 01/21/2019 at 7:11 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 01/21/2019 at midnight.


The Bottom Line

Increasing wind today will create very dangerous avalanche conditions. Wind slabs will build from the abundant recent snow accumulation that are likely to avalanche naturally. The SE half of the compass rose is likely to produce the largest avalanches today, but wind from nearly every direction in the past 24 hours means that choosing terrain to avoid wind slab avalanche danger today will be all but impossible.  Avalanche danger will increase to HIGH today. Travel in avalanche terrain is not recommended. The Southern gullies of Huntington Ravine, the Left side of Tuckerman Ravine, and elevations below 3500’ are the exceptions but remain at CONSIDERABLE avalanche danger. Terrain lacking wind affected snow, like low elevations, will hold storm slabs which you are likely to trigger.

2019-1-21_printable_pdf

Forecast Area

The USDA Forest Service Mount Washington Avalanche Center has issued a backcountry avalanche warning for the Presidential Range.  Avalanche warning criteria may also be met in other areas outside those forecast by the avalanche center. This avalanche watch does not apply to operating ski areas.

Avalanche danger will increase through Monday, January 21, 2019, with very dangerous avalanche conditions on and below slopes steeper than 30 degrees. Natural avalanches will be likely. Travel in avalanche terrain is not recommended.

Recent heavy snowfall will combine with steadily increasing wind to create unstable conditions likely to produce large avalanches.  Wind from the NNW is forecast to increase from 40 mph to 80 mph by Monday evening, with higher gusts.

Mountain Weather

The recent snow storm totaled 13” at the Hermit Lake and Harvard Cabin snow plots and 12“ at Gray Knob. After a cold start to the day on Sunday that produced lighter density snow, temperatures reached 25F on the summit yesterday afternoon, which in combination with warm air aloft allowed for a period of denser snow accumulation. Wind from the SE around 45 mph on the summit shifted W then NW overnight, bottoming out at 20 mph with a current speed of 28 mph. Today’s key weather factor will be wind which is forecast to blow from the NNW and increase slowly to 70 mph with gusts to 90 mph by dark. We may receive another trace to one inch of snow accumulation as cloudy cover persists and temperatures will only rise a few degrees above the current -14.5F on the summit. Wind will continue to increase to sustained 100 mph speeds with stronger gusts by early tomorrow before dropping off slightly through the day. Skies should become clear with temperatures rebounding to the single digits above 0F by tomorrow afternoon.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind from the NNW forecast to increase through the day will build large unstable slabs from the recent storm snow. Expect new slabs to form on the SE half of the compass rose and be touchy to a human trigger. Additionally, reactive and small to large in size slabs formed from yesterday’s wind direction (SE) make wind slabs a concern on all aspects and elevations above 3500’ today. These windward slopes may become scoured by this evening, but hold unstable slabs this morning.

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.

Secondary Avalanche Problem – Storm Slab

Storm Slab

Aspect/Elevation

Likelihood

Size

Storm slab from our recent heavy snowfall exists anywhere in the terrain that you don’t find wind slab. Human triggered avalanches remain likely in this reactive layer. The storm snow has an upside down character, with more dense and cohesive snow over less dense snow. This more dense snow showed an ability to propagate a crack a relatively long distance yesterday and result in avalanches entraining all storm snow.

What is a Storm Slab Avalanche?

  Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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 snow storm of the past two days has result in widespread unstable conditions for a variety of reasons. Wind predominantly from the SE as well as a variety of other directions yesterday built slabs in lee and cross loaded areas yesterday, which we expect to remain touchy to a human trigger this morning. Other terrain holds storm slab that is similarly touchy. Northwesterly wind today will increase and transport the abundant snow available in our fetch zones to build larger slabs than those already existing in the terrain. This wind slab that builds today will likely produce large, natural avalanches. The variety of surface slabs sit on generally smooth bed surfaces, including widespread hard wind slab, some softer snow, and areas of December 22 crust. A few areas may present potential for avalanches today to step down or entrain deeper layers of snow to increase overall size, but most terrain that will be loaded by today’s wind has limited potential in this regard. That said, avalanches today could be quite large from the wind loaded storm snow alone. Today is a great day to enjoy soft snow in lower angled terrain or at a ski area.

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
03/26/19
05:30
0 CM 0 MM0CM245 CM-16.0 C-7.0 C-16.0 CClearNo precipitation
03/25/19
05:20
3 CM 1.7 MM 9%3CM249 CM-12.0 C-2.0 C-12.0 CBrokenNo precipitation
03/24/19
05:19
0 CM 4.0 MM32CM250 CM-10.5 C-5.0 C-13.0 CClearNo precipitationView
03/23/19
05:17
38 CM 38.6 MM 12%NC253 CM-5.5 C-2.5 C-5.5 COvercastSnowView
03/22/19
05:20
Trace Trace NC213 CM-4.0 C3.0 C-4.0 COvercastSnowView

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
03/25/1911 F-3 F .15 in 1.7 in56.5 MPH86 MPH

270 (W)

03/24/1914 F1 F .21 in 3.4 in74 MPH123 MPH

310 (NW)

03/24/1918 F4 F Trace in 0.1 in63.2 MPH98 MPH

290 (WNW)

03/23/1914 F1 F 0.21 in 3.4 in74.4 MPH123 MPH

310 (NW)

03/22/1924 F12 F 1.09 in 15.2 in38.9 MPH79 MPH

330 (NNW)

View
03/21/1926 F15 F 0.02 in 0.3 in28.8 MPH60 MPH

160 (SSE)

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)

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 01/21/2019 at 7:11 AM.

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