Avalanche Forecast for Thursday, April 18, 2019

This forecast was published 04/18/2019 at 7:01 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 04/18/2019 at midnight.


The Bottom Line

New wet snow falling this afternoon on high winds may contribute to wet snow avalanche problems as older wind slabs turn wet. Wet loose avalanches, or sluffs, are also possible today, even on the older snow surface. Sluffing will be more intense in areas of Monday’s drier snow, which appears white when compared to the darker, melt/freeze surface. Beware of the sliding fall potential that exists today particularly on shady areas this morning. Any avalanche activity today should be easily avoidable and limited to the more recent snow becoming wet in the sun or being further loaded this afternoon by up to an inch of new snow drifting on increasing winds. LOW avalanche danger exists today in all forecast areas.

2019-4-18 Printable

Forecast Area

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Mountain Weather

A warming trend starts today which will eventually bring above freezing temperatures to the summit elevations. The freeze line is around 4300’ on the Auto Road with Gray Knob at 25F and 36F at Hermit Lake at 5:30am. Temperatures will continue to climb to 39F on the summit by mid-afternoon. Wind from the southwest, currently at 32mph, will increase through the day with 45-60 mph mid-day and 60-70 mph range by nightfall. Mostly clear skies this morning will gradually fill in with cloud cover as precipitation arrives this afternoon. A trace to an inch of wet snow may fall this afternoon. Another low pressure system brings more rain showers tomorrow with temperatures near 47F on the summit.

Primary Avalanche Problem – Wet Slab

Wet Slab

Aspect/Elevation

Likelihood

Size

Wind slabs that formed from snowfall on Monday have been unreactive but could become wet today if precipitation turns wet. An inch of snowfall or rain on increasing winds today on our existing icy bed surface could set the stage for some small avalanches. Keep a close eye on the weather today.

  Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

Secondary Avalanche Problem – Wet Loose

Wet Loose

Aspect/Elevation

Likelihood

Size

Wet loose snow avalanches may grow large enough to push you around the terrain today. Consider strategies to manage these and bear in mind that more recent snow may be harder to handle and entrain more snow than the older melt/freeze surfaces.

  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.

Snowpack and Avalanche Discussion

There has been no reported avalanche activity since April 11th. Yesterday, the inch of new snow which fell on Monday provided quality turns in the Tuckerman Headwall but the shadier Ammonoosuc Ravine failed to soften. Today, the strong April sun should have time to work it’s magic again before clouds move in and new snow or rain falls this afternoon. All aspects should soften today as the freeze line rises to summit elevations. The deeper snowpack is generally isothermal which reduces our concerns for larger avalanches. No freeze overnight will bring a return of significant hazards due to melting tomorrow. Lots of rain on snow increases the risk of undermined snow over swollen rivers, along with ice and rock fall. From a recreationist’s perspective, nothing good comes from rain on snow.

Additional Concerns

The Sherburne and Gulf of Slides ski trails are snow covered to Pinkham Notch, though this is changing by the day. Expect ice patches, opening stream crossings and the occasional bare patch.

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.

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
11/20/19
06:18
3 CM 9.4 MM 21%3CM19 CM-2.5 C1.5 C-2.5 COvercastNo precipitation
11/19/19
06:15
0 CM 5.9 MM0CM17 CM1.0 C2.0 C-10.0 COvercastRain
11/18/19
06:20
0 CM 0 MM0CM21 CM-6.0 C-4.5 C-11.5 CBrokenNo precipitation
11/17/19
06:20
0 CM 0 MM0CM23 CM-11.5 C-9.0 C-14.0 CClearNo precipitation
11/16/19
07:00
3 CM 2.3 MM 11%3CM23 CM-13.5 C-5.0 C-14.0 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 04/18/2019 at 7:01 AM.

Frank Carus
USDA Forest Service
White Mountain National Forest