Avalanche Forecast for Monday, February 18, 2019

This forecast was published 02/18/2019 at 6:58 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 02/18/2019 at midnight.


The Bottom Line

Slabs that formed late last week into Saturday remain possible to human trigger today with the greatest likelihood being for small avalanches in softer wind drifted snow. Large avalanches in firmer wind slab are not yet ruled out. A small skier triggered avalanche on a low consequence terrain feature yesterday is a pertinent example what you might find today. Check this out on our observations page and thanks for this and similar observations. Consider the consequences of either a small or large avalanche in terrain you choose today, and realize that low visibility might affect your ability to assess terrain. All forecast areas have MODERATE avalanche danger.

2019-2-18_printable_pdf

Forecast Area

Avalanche Safety Information Study

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Mountain Weather

Clear skies and light to moderate wind yesterday gave way to clouds overnight. Snow began falling early this morning, with 1-2” forecast for today. Wind should remain light through the day, shifting NW and increasing this evening as snowfall tapers off. The current summit temperature of 7F should hold through the day. Overnight, temperatures will drop towards -10F by tomorrow morning as cloud cover decreases and NW wind approaches 70 mph with stronger gusts. Tomorrow should bring mostly clear skies with summit temperatures in the single digits F below 0 and continued NW wind around 70 mph.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slabs on many aspects, formed late last week on varied wind speed and direction, have generally become stubborn to a human trigger. You’re more likely to trigger an avalanche in softer pockets where your skis or boots sink into the slab. The possibility of a large avalanche does remain, particularly where the snow has a hollow sound. New snow on increasing NW wind may build new reactive but small slabs by late today or tonight.

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

The robust crust that was widespread in our terrain has mostly been covered by wind slabs formed since Wednesday at middle and upper elevations. The layered slabs above the crust formed on multiple periods of westerly and southerly wind and as recently as Saturday, with small new slabs likely to develop late today. As of yesterday, surface slabs were generally firm (1F +/-) and supportable under skis, with softer pockets of greater ski penetration and certainly boot penetration existing also. We suspect these softer pockets could behave similarly to the small skier triggered avalanche in the Ammonoosuc Ravine yesterday. A firm over soft structure has been identified in the slabs formed above the crust, keeping large avalanches a relevant though less likely concern. Keep this possibility as well as the spatial variability inherent to wind slabs in mind as you make snowpack observations today.

Additional Concerns

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

Please join us for an evening of avalanche awareness at Flatbread Company in North Conway this coming Thursday!

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 02/18/2019 at 6:58 AM.

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