Avalanche Forecast for Wednesday, April 24, 2019

This forecast was published 04/24/2019 at 7:17 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 04/24/2019 at midnight.


The Bottom Line

Spring hazards remain through most of the day though new snow and wind slab development is possible this afternoon. Our snowpack hasn’t refrozen for six days which makes wet loose avalanches a concern. A skier triggered but was not captured by a D1 or 1.5 wet loose avalanche in Left Gully yesterday. These types of avalanches are often harmless if carefully managed but if not, they can push you over cliff bands, into crevasses or moat. Undermined snow over flowing streams remains a threat though peak flow has subsided following recent rain and warmer temperatures. Assess the weather carefully this afternoon and bear in mind that any new wind slabs that develop are likely to be sensitive to human-triggering. Avalanche danger is LOW today.

2019-4-24_printable_pdf

Forecast Area

Avalanche Safety Information Study

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Mountain Weather

Morning showers, cloudy skies and temperatures again above freezing yesterday gave way to overnight showers with .18” of rain recorded on the summit. The overnight low temperature was 37F which is where we start the day. Precipitation is expected to continue today with temperatures on the summit slowly making their way back to freezing and below, reaching the upper 20sF in the afternoon. Rain may transition to mixed precipitation, including snow with a trace to 2” possible. West wind at 50 mph this morning will shift to the NW, decrease to 25-40 mph mid day before increasing to 40-55 mph this evening.  The chance for snow showers continues overnight with up to 1” possible. Partial clearing skies tomorrow, summit temperatures in the mid 30’sF and light NW wind expected.

Primary Avalanche Problem – Wet Loose

Wet Loose

Aspect/Elevation

Likelihood

Size

It is possible for skiers to initiate wet loose sluff avalanches on steep terrain today. While small in size, these slow moving sluff avalanches have the ability to entrain skis and carry a person to an undesirable location such as one of the many sizeable glide cracks or cliffs found on our steeper slopes.

What is a Wet Loose Avalanche?

  Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Secondary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

New snow this afternoon may combine with a NW wind to create the potential for wind slabs on easterly aspects. Size, sensitivity and location of this avalanche problem depends on an uncertain weather forecast of precipitation types. Watch for developing wind slabs this afternoon if the rain turns to snow.

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 summit of Mount Washington has not been below freezing since the 18th, allowing heat and moisture to penetrate deep into our snowpack. Significant melting has occurred, bringing springtime objective hazards to the forefront. If you are in the mountains today be watching for:

We did not name Wet Slab as an avalanche problem today, partially due to the fact that we believe peak water levels flowing into and through the snowpack has passed, and also the chance for new wind slabs developing as the temperature falls below freezing.  With water likely to be flowing in the stream under The Lip area, spending time on the floor of Tuckerman Ravine should be avoided today.

Tuckerman Ravine Headwall, April 22, 2019. How many springtime hazards named above can you spot?

Additional Concerns

The Sherburne and Gulf of Slides ski trails are no longer completely snow covered to Pinkham Notch. Expect ice patches, open stream crossings, rocks and bare patches. We will likely be closing a lower section of the Sherburne soon in order to prevent destructive erosion of the trail. When we do, please do your part to preserve the quality of the trail by removing your skis and hiking the rest of the way down to Pinkham on the Tuckerman Ravine Trail.

Help us improve the backcountry avalanche forecast! We are working with partners in Canada to better understand how we communicate the avalanche risk, and we need your help. Please fill out this survey. It will take a few minutes, but it will help us as we work on new ways to give you the most important avalanche information.

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 04/24/2019 at 7:17 AM.

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