Avalanche Forecast for Friday, February 21, 2020

This information was published 02/21/2020 at 7:05 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 02/21/2020 at midnight.


The Bottom Line

While human triggered avalanches are possible today, snowpack evaluation and terrain management will provide ample recreation for those looking to ski and climb. Wind drifted snow exists on many aspects and has a MODERATE rating for the day. Be wary of convex or unsupported snow slopes as you move around. If the snow underfoot changes from supportable to postholing or “grabby” skiing, it’s probably time to take another look at where you are and investigate why the snow structure suddenly changed. Places that have been scoured by this week’s wind may lack today’s avalanche problem and offer generally safe conditions.

2020-02-21 Printable


Mountain Weather

Yesterday, no snowfall was recorded. Temperatures remained below 0F above 4000’. Wind shifted between W and WNW, starting the day at 70mph and gradually decreasing to 35mph, where it currently sits.

Today, expect mostly sunny skies. Current below 0F temperatures should gradually warm through the day to 5F on the summits by sunset. Wind will increase to above 50mph from the W.

Tomorrow should start clear with strong wind from the W. Upslope snow showers may produce a measurable amount of snow in the afternoon and nighttime. Temperatures will increase significantly on Sunday. It is possible that everything under 5500’ will go above freezing.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Firm, stubborn wind slabs exist on many aspects due to varying wind direction mid-week. Expect to find several interfaces and layers of new snow when you dig today. While propagation was minimal in limited field time yesterday, the spatial variability encountered demanded getting hands in the snow to see what each slope consisted of. You may find thinner wind slabs in protected areas that are more susceptible to triggering. The outside chance of a large avalanche is unlikely today, though the size of the natural avalanche cycle that occurred Tuesday into Wednesday should provide a reminder of what is possible and that we are finally in a fully developed snowpack.

  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.

Forecast Discussion

It’s been a rough past few days to get in the field thanks to the combined forces of wind and cold. Because of this, a degree of uncertainty exists in today’s avalanche forecast. History has shown us that when wind blows as long and as strong as it did, we are usually left with a mix of scoured ice, sastrugi, and unreactive wind slab. A brief trip into terrain yesterday afternoon confirmed some of these suspicions, but not enough for us to say unreactive with confidence. Today’s improved weather will likely drive people into terrain and hopefully you send us your feedback through our observations page.

Additional Information

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

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
04/03/20
05:10
4 CM 30.6 MM 37%NC168 CM-1.0 C-0.5 C-1.0 COvercastRain
04/02/20
05:25
Trace 0.1 MMTrace165 CM-0.5 C0.0 C-11.5 COvercastSnow
04/01/20
05:30
0 CM 0.0 MMTrace166 CM-10.5 C6.5 C-11.0 CClearNo precipitationView
03/22/20
05:07
0 CM 0 MM0CM145 CM-18.0 C-5.0 C-18.0 CClearNo precipitation
03/21/20
05:10
Trace 1.6 MMNC145 CM-9.5 C12.0 C-9.5 COvercastSnow

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
03/20/2043 F20 F 0.31 in 0.2 in66.5 MPH145 MPH

260 (W)

03/19/2036 F14 F 0.02 in 03 in26.5 MPH50 MPH

180 (S)

03/18/2021 F9 F 0.03 in 0.5 in39.7 MPH94 MPH

290 (WNW)

03/17/2021 F6 F 0.25 in 2.1 in52.4 MPH109 MPH

280 (W)

03/16/2014 F1 F 0 in 0 in21.3 MPH50 MPH

240 (WSW)

03/15/207 F-3 F 0.0 in 0.0 in42.1 MPH71 MPH

300 (WNW)

03/14/2014 F6 F 0.09 in 0.7 in76.9 MPH117 MPH

270 (W)

View
03/13/2032 F12 F .43 in 1.4 in64.3 MPH94 MPH

270 (W)

03/12/2022 F14 F .02 in .2 in27.4 MPH48 MPH

210 (SSW)

03/11/2024 F9 F 0.02 in 0.2 in47.3 MPH85 MPH

300 (WNW)

03/10/2035 F24 F 0.45 in 0.5 in52.1 MPH97 MPH

260 (W)

03/09/2034 F21 FTrace Trace 57 MPH84 MPH

270 (W)

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 02/21/2020 at 7:05 AM.

Helon Hoffer
USDA Forest Service
White Mountain National Forest