Avalanche Forecast for Saturday, February 29, 2020

This information was published 02/29/2020 at 7:05 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 02/29/2020 at midnight.


The Bottom Line

Human triggered avalanches are possible today where west wind will combine with forecast snow to form new wind slabs. Watch for signs of wind transported snow loading slopes in the lee of the wind, especially in steep terrain and cross loaded gullies. New wind slabs formed today will feel softer under-foot than the existing wind slabs in our terrain formed from Thursday’s storm. Evaluate snow and terrain carefully. Avalanche danger is MODERATE today.

2020-2-29 Printable Forecast


Mountain Weather

Yesterday 1.9” (SWE 0.21”) of snow was recorded on the Mt Washington summit while W wind remained steady at 60-80 mph, and decreasing overnight.  Temperatures hovered around 0F. 

Today, snow showers may bring a trace to 2” of new snow on a W wind 25-40 mph shifting NW in the afternoon. The chance for snow showers will be greatest mid-day, mainly before the wind shifts NW signaling drier air moving in. Temperatures on the summit will remain in the single digits below 0F. Light snow showers remain a possibility overnight. 

Tomorrow, a trace to 1” of additional snow as snow showers is possible with NW wind 40-50 mph.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Large wind slabs formed from Thursday’s 9.5” (17%) snow are likely to be stubborn but remain possible to trigger, particularly where they exist outside the more active avalanche paths. Wind slabs forming today from new snow and moderate wind speeds will be more reactive to a human trigger and may grow to a foot thick or more if we see the upper end of the forecast total. Since new snow today will be limited to upslope snow showers, middle and upper elevations are the main concern. If you find thick drifts of soft snow today, you’ve found the avalanche problem. 

  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

Thursday’s storm is proving to be an interesting one for forecasters. First, the storm was responsible for a number of natural avalanches in our terrain including Hillman’s, Duchess, Empress, Left Gully, South Gully and Escape Hatch. Escape Hatch may have stepped down deeper into the existing snowpack, possibly failing on a facet layer near an ice crust formed during one of many warm-ups that we’ve had this winter.

Avalanche debris under Escape Hatch, Huntington Ravine. 2/28/2020

Second, the 9.5” of 17% snow has stabilized quickly, likely due to the moisture content of the snow, followed by cold temps and wind. Field time yesterday showed the snowpack to be firm, pencil to 1F and stubborn. A human triggering these wind slabs would be unlikely in the majority of our terrain, though unfortunate since they are quite thick. 

Additional Information

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

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
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
03/20/20
05:05
0 CMTrace 0CM154 CM7.0 C8.5 C-4.5 CClearNo precipitation
03/19/20
05:10
0 CM 0.0 MM0CM156 CM-1.5 C3.0 C-7.5 CClearNo precipitation
03/18/20
05:41
1 CM 3.0 MM1CM157 CM-8.0 C-2.5 C-10.0 CFewNo precipitationView

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 02/29/2020 at 7:05 AM.

Jeff Fongemie
USDA Forest Service
White Mountain National Forest