Avalanche Forecast for Friday, February 15, 2019

This forecast was published 02/15/2019 at 7:05 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 02/15/2019 at midnight.


The Bottom Line

Rain falling on snow brings the possibility of wet slab avalanches on steep terrain at lower to middle elevations today. Wind sheltered areas that accumulated snow over the past two days will be most affected and have MODERATE avalanche danger due to the possibility of human-triggering. Be cautious if you find boot top or deeper snow that is getting rained on. New wind drifted snow at higher elevations today will be falling on wind slabs which continued to develop in high winds yesterday. The new load of snow keeps danger ratings elevated into the CONSIDERABLE rating, but just barely. There is a lingering possibility of natural avalanches in isolated areas of mid-elevation terrain where larger wind slabs remain from the previous storm. Most human-triggered wind slab avalanches today would be smaller, though still potentially dangerous.

2019-2-15 Printable

Forecast Area

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Mountain Weather

The wind diminished slowly through the afternoon yesterday, after a steady strong west wind (60-70 mph gusting to 90) through the early morning hours. Temperatures today are rising from yesterday’s low of -4F. Snow will start early this morning and continue through the day and into the evening. A water equivalent of 0.7” of should fall on the area equating to possibly 3-5” of snow at higher elevations. The temperature on the summit is forecast to reach 27F late in the afternoon which may mean that the freeze line will rise into mid-elevation avalanche terrain. Rain seems certain at lower elevations in our forecast area. South winds will move snow today. Cold temps return tonight with upsloping snow showers bringing another 1-3” of snow to the higher summits.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

The 3-5” of new snow today will build the largest wind slabs on northerly aspects and crossload others. These wind slabs will be largest beneath steep terrain features and near the tops of gullies, particularly those with a good amount of fetch like South and Odell Gully in Huntington and the Great Gulf Headwall. Today’s wind slabs may form on slabs formed since Wednesday, which will be less reactive to a human trigger but could keep larger avalanches a possibility today.

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 – Wet Slab

Wet Slab

Aspect/Elevation

Likelihood

Size

Snow will turn to rain which will add load and weaken snow on the ground and may lead to human triggered avalanches. Steep areas of accumulated snow, such as you might find beneath pitches of ice or rock slab in Webster gullies, could be especially problematic if rain water flows beneath as well as on the existing soft slabs.

What is a Wet Slab Avalanche?

  Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

Snowpack and Avalanche Discussion

Field time during a brief period of marginally improved visibility allowed a trip into Tuckerman Ravine where the floor was completely wind scoured to old refrozen surface with patches of old surface peppering steep terrain too. Smaller sized piles of avalanche debris indicated small to medium sized avalanches had released in the Lip and Left Gully. Hillman’s Highway had the largest and most obvious debris pile and a 16-18” crown line was visible beneath the steep ice on the buttress above the middle-right side of Lower Snowfields. The absence of large or widespread avalanche debris combined with the the weather and snow history leads me to believe that the avalanche cycle was widespread soft slabs running frequently and early as the snow fell Tuesday and Wednesday. The storm slabs failed to adhere well enough to the icy bed surface to build large slab except in isolated areas. Those isolated areas are the places capable of producing the biggest avalanche today.

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
05/31/19
05:20
0 CMTrace 0CM0 CM8.0 C11.0 C0.5 CBrokenNo precipitation
05/30/19
05:25
0 CM 0.0 MM0CM0 CM7.5 C7.5 C1.0 CScatteredNo precipitation
05/29/19
05:25
0 CM 22.3 MM0CM0 CM1.5 C4.0 C0.0 COvercastNo precipitation
05/28/19
05:25
0 CM 0.0 MM0CM0 CM0.5 C11.0 C0.5 CClearNo precipitation
05/27/19
05:15
0 CM 0.0 MM0CM10 CM8.0 C15.5 C8.0 CClearNo precipitation

Avalanche Log and Summit Weather

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
05/30/1946 F36 F 0 in 0 in27.9 MPH55 MPH

290 (WNW)

05/29/1947 F33 F 0 in 0 in20 MPH48 MPH

290 (WNW)

05/28/1934 F28 F .71 in 3.7 in20 MPH48 MPH

290 (WNW)

05/27/1940 F27 FTrace 0 in38.9 MPH68 MPH

300 (WNW)

05/26/1948 F39 F .77 in 0 in48.7 MPH75 MPH

290 (WNW)

05/25/1947 F31 F .42 in 0 in17.7 MPH63 MPH

240 (WSW)

05/24/1942 F32 F .66 in 0 in44.8 MPH105 MPH

05/23/1944 F30 F .16 in 0 in26.8 MPH71 MPH

270 (W)

05/22/1934 F21 F 0 in 0 in36.2 MPH115 MPH

330 (NNW)

05/21/1934 F23 F .57 in 1.9 in73 MPH135 MPH

330 (NNW)

05/20/1951 F33 F 0.57 in 0.0 in48 MPH82 MPH

250 (WSW)

05/19/1951 F34 F .6 in 0 in34.2 MPH66 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 02/15/2019 at 7:05 AM.

Frank Carus
USDA Forest Service
White Mountain National Forest