Avalanche Forecast for Wednesday, April 10, 2019

This forecast was published 04/10/2019 at 7:15 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 04/10/2019 at midnight.


The Bottom Line

New wind slabs formed from drifting snow overnight may be possible to human trigger. Assess smooth areas of new snow to avoid this avalanche problem. With colder temperatures today, the wet older snow from Monday will be refreezing though the day, resulting in a hard icy surface capable of sustaining a long sliding fall, especially later in the day. An ice axe, crampons and your ability to not fall will be required once the existing snow freezes. A small avalanche could easily cause a sliding fall. Avalanche danger is MODERATE today, evaluate snow and terrain carefully.

2019-4-10_printable_pdf

Forecast Area

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Mountain Weather

Yesterday, the summit of Mount Washington reached a high temperature of 32F with middle and lower elevations remaining well above freezing. The temperature dropped in the afternoon enough for evening precipitation to fall as snow showers, with 1.9” recorded on the summit on WSW wind at 50 mph. The Hermit Lake Snow Plot recorded 2.75” of snow in the past 24 hours. Today, we start the day with 9F on the summit rising only to the mid teens F in the fog under cloudy skies. NW wind will diminish a bit mid-day but otherwise remain fairly steady at 45-60 mph.There is a chance of snow showers with accumulations of a trace to 2”, mainly in the morning. Tomorrow’s forecast offers more settled weather as high pressure brings clear skies, light/moderate winds and summit temperatures in the low 20s F.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

New wind slabs formed from overnight snow may be reactive to a human trigger. These wind slabs will be found mainly on the eastern half of the compass at elevations above 3500’ beneath and in the lee of steep terrain features.. Look for wind drifted snow as the avalanche problem today which will appear as soft, smooth areas of new snow. In locations where the slabs are thickest and reactive, they could be large enough to carry and perhaps bury a person.

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 roughly 3.5 inches of mixed precip types that fell on upper elevations on Monday, were ultimately wetted to the bed surface at ravine levels by several hours of freezing rain in the late afternoon & evening. Warm air Tuesday morning melting an ice crust may also have played a part in adding water to Monday’s snow. Due to southern wind direction with limited fetch, moderate wind speeds, dense, sticky snow and possibly an ice crust, drifting snow was limited resulting in an evenly distributed covering of snow. By Tuesday, this moist snow covering was found at all levels in the ravines. Overnight, temperatures dropped well below freezing at mid and upper elevations which will eventually freeze the existing snowpack solid, if it hasn’t done so already. Any instabilities in the snowpack today will be limited to new windslab formed from the 1.9” of snow recorded on the summit overnight.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch with some open water at low elevations.

Details on daily snowfall totals, precipitation type, total depth of snow and other information can be found on our page devoted to snow study plot data. Click here to check it out.

Recent snowpack and avalanche observations can be found here and on Instagram. Your observations help improve our forecast product. Please take a moment and submit a photo or two and a brief description of snow and avalanche information that you gather in the field.

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 04/10/2019 at 7:15 AM.

Jeff Fongemie, Snow Ranger
USDA Forest Service
White Mountain National Forest