Avalanche Forecast for Thursday, February 14, 2019

This forecast was published 02/14/2019 at 7:06 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 02/14/2019 at midnight.


The Bottom Line

Wind from the west will continue at speeds sufficient for creating wind slabs in the eastern half of the compass rose this morning. Storm slabs also exist on all aspects where 15” of snow has fallen in the past 36 hours. All avalanche terrain, especially at mid and upper elevations, has CONSIDERABLE avalanche danger due to the likelihood of human-triggered avalanches. Both of these avalanche problem types are capable of producing an avalanche that is easily large enough to bury a person. If you plan to ski in avalanche terrain, keep it low angle on smaller, wind sheltered slopes. Minor wind effect on the snow could bring down a wind slab from above.

2019-2-14 Printable

Forecast Area

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Mountain Weather

Continuous snow showers yesterday dropped another 5” of new snow at mid and upper elevations. Add this new, lower density snow (11%)  to the 10” that fell Tuesday night for a total of around 15” in the alpine. The critical detail in the weather history is the lower than expected and variable wind speeds over the past 24 hours. Wind velocity averaged only in the 45 mph range from the west which failed to move much of the dense and heavy new snow. This morning’s higher wind speeds in the 70 mph range will be diminishing to the 35-50 mph range but shifting to the NW. Temperatures dropped quite a bit over night to around -2F but will rebound to 10F on the summit and around 20F at 2,000’.

Primary Avalanche Problem – Storm Slab

Storm Slab

Aspect/Elevation

Likelihood

Size

Fifteen inches of snow has fallen in the past 36 hours. The snow started dry, became wetter and then dried out again. The wetter layer showed signs of dangerous slab forming properties yesterday. This new snow is sitting on top of a refrozen, icy crust which makes an ideal sliding surfaces that could produce full extent avalanches in gullies and larger slopes. Turn around if you see cracks shooting from your ski tips or slab failures at kickturns.

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.

Secondary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Today’s wind slab problem will be harder to avoid than our typical wind slabs. Wind speeds weren’t high enough to scour snow down to old surface or create the stubborn wind slabs we’re more familiar with here. Hollow snow piled beneath steep terrain features and at the skyline may fail naturally, but skiing across hollow wind drifted snow on a slope over 30 degrees will likely produce an avalanche large enough to carry and bury you.

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

Visibility was very limited yesterday and we received no observations from the field. On one hand, this is good news because anyone in steep avalanche terrain would have likely reported being involved in an avalanche. Small test slopes below treeline showed fair stability but some wind at the ridge top indicated that stability would have been reduced there. Those of us that easily fall in love with steep, smooth snow will run the risk of being blinded by Cupid’s arrow today. Please remember to make an alternative plan this morning that will allow you be satisfied by skiing lower angled, protected slopes. More snow is on the way Friday and will likely keep avalanche danger elevated once again.

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 02/14/2019 at 7:06 AM.

Frank Carus
USDA Forest Service
White Mountain National Forest