Avalanche Forecast for Tuesday, March 12, 2019

This forecast was published 03/12/2019 at 7:08 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 03/12/2019 at midnight.


The Bottom Line

Wind in the 70-90 mph range from the west continues to affect our new snow and load terrain on the eastern half of the compass rose. The resulting firm wind slabs are possible to trigger in most of our terrain. East and Southeast facing terrain, like the Headwall of Tuckerman Ravine and to a lesser extent the Gulf of Slides, should have the largest new wind slabs and will receive the greatest wind loading today. Due to this continued loading, human triggered avalanches will be likely and natural avalanches will be possible, giving the Headwall of Tuckerman Ravine a CONSIDERABLE avalanche danger rating today. Other forecast areas have MODERATE avalanche danger, with LOW avalanche danger for the Northern Gullies in Huntington Ravine due to scouring of new snow.

2019-3-12_printable_pdf

Forecast Area

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Mountain Weather

Snowfall in the past 24 hours has totaled 4.4” on the summit, bringing the 48 hour total to just over 8”. Our snow study plots recorded nearly 4” of new snow yesterday as well. Sustained W wind of 70-90 mph yesterday has begun to shift NW, where it should remain through the day with little change in wind speed. Another trace to 2” of snow will fall today, predominantly this morning, as cloud cover decreases through the day. Summit high temperatures should be in the single digits F above zero, rising only slightly from the current -1F. Tomorrow brings decreasing wind speeds, temperatures rising to around 20F on the summit, and a slight chance of mixed precipitation in the evening or after dark.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slabs built on westerly wind since late Sunday are our primary avalanche problem. Given the extreme wind speeds, expect these slabs to generally be stubborn to a human trigger but deserving of respect due to being recently formed. East facing terrain in the lee of recent and current wind will hold the largest new slabs, with cross loading and terrain-driven variation in wind direction likely loading all aspects on the eastern half of the compass rose. Our recent wind speeds tend to scour upper start zones and build slabs slightly lower in our avalanche paths. Significant graupel has been noted at snow plots, which tends to pool relatively low in avalanche paths where it may act as a weak layer.

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

New snow and wind in the past 48 hours are the primary factors driving instability in our snowpack at this time. The snow initially fell on southerly wind, loading northerly terrain, before shifting W and increasing since late Sunday. Our recent and forecast wind speeds tend to build firm and stubborn wind slabs and also scour the most wind exposed lee terrain which would be loaded on lower wind speeds. The recency of formation and continued loading of these hard slabs means that though stubborn, they’re likely not well bonded to older layers. Our windward west facing terrain should be quite scoured at middle and upper elevations and generally lack this avalanche problem. Lower elevations have received less new snow, and while pockets of wind thicker wind slab may exist, this terrain also tends to lack today’s primary avalanche problem. The new slabs lie on a number of layers of older wind slab, formed predominantly last week, that seem to have become unreactive. We don’t expect an avalanche in the new wind slab to step down to these older layers, but it’s not impossible.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch. Don’t miss our final Avalanche Awareness presentation of the season, one week from today at Plymouth State University, details are on our events page.

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 03/12/2019 at 7:08 AM.

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