Avalanche Forecast for Saturday, February 23, 2019

This forecast was published 02/23/2019 at 7:03 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 02/23/2019 at midnight.


The Bottom Line

Skiers and climbers could trigger an avalanche in wind slabs that formed Thursday into Friday in steep terrain today. Natural avalanches in Left Gully and Hillman’s Highway during that period are reminders that our snowpack is still dynamic. Given the well-developed and connected nature of avalanche paths on east side of the Presidential Range, the consequences of producing an avalanche today could be severe. The possibility of triggering a wind slab today combined with the potential of this initiating a large avalanche gives today’s avalanche problem a MODERATE rating. Exposing one person at a time to the hazard combined with careful snowpack evaluation could result in quality recreation. Solid partners wearing a beacon and carrying probes and shovels are another tool to lower the consequence level of finding a weak spot and triggering an avalanche. It is unlikely that a person could trigger the underlying wind slabs that formed earlier in the week, but these could be triggered by a the mass of a smaller avalanche.

Printable 2019-02-23

Forecast Area

Mountain Weather

While those on the mountain yesterday found cold temperatures and a stiff wind, ample sunshine made it manageable and downright pleasant at times. Wind blew from the NW all day and remained in the 40 mph range. Temperatures stayed in the single digits above 5500’ with 0.2” of snow falling through the day. High pressure sliding over the region today will allow NW wind speeds to dampen into the teens with temperatures cresting 20F on the summit. Clear skies to start the day will be replaced by clouds later as tomorrow’s storm approaches. Snowfall will start after midnight and have significant accumulation before temperatures warm enough in the afternoon to bring possible mixed precipitation.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Wind slab that is stubborn to a human-trigger exists on most terrain on the eastern half of the range. Distribution of this wind slab on terrain with an easterly aspect is abundant; avoiding today’s avalanche problem will be difficult if traveling in avalanche terrain. Mitigating your exposure to the hazard is the name of the game today. While the snowpack displays only fair strength and a structure conducive to instability, multiple field tests yesterday identified a lack of energy to propagate a crack in both the surface wind slab and deeper layers.

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

Avalanche paths in Ravines are large and connected.

A multi-layered wind slab sits on top of the February 8 ice crust. Over the past two weeks as these layers formed, signs of instability were displayed through both natural and human-triggered avalanches, though high winds and warm daytime temperatures late this past week have allowed a degree of sintering and bonding within the snowpack. The surface wind slab presents with an upside-down structure on a weak layer that contains graupel. Further down in the snowpack, very firm (harder than pencil), older wind slab exists with a thin weak layer just above a proven, active  bed surface (Feb 8 crust). The potential for an avalanche to step down to the bed surface seems unlikely, but has the potential to turn a small avalanche into a large one that extends into more than one avalanche path. While temperatures below 3500’ should remain below freezing, strong solar gain is likely today at lower elevations and could weaken lingering slabs, particularly on steep south-facing aspects. Bright sun on sheltered areas with softer slabs are warning signs that could also be accompanied by roller balls where soft snow exists. Limited warming at higher elevations could increase cohesion of surface slabs as well.

Additional Concerns

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

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
03/22/19
05:20
Trace Trace NC213 CM-4.0 C3.0 C-4.0 COvercastSnowView
03/21/19
05:23
0 CM 0 MM0CM213 CM-1.5 C0.0 C-11.5 COvercastNo precipitation
03/20/19
05:28
0 CM 0 MM0CM214 CM-11.0 C-4.5 C-14.0 CClearNo precipitation
03/19/19
05:25
0 CM 0.0 MMNC215 CM-13.0 C-9.5 C-15.0 CFewNo precipitation
03/18/19
05:20
Trace 0.1 MMNC216 CM-15.5 C-13.0 C-15.5 CBrokenSnowView

Avalanche Log and Summit Weather

Daily Observations


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
03/20/1917 F1 F 0.0 in 0.0 in32 MPH58 MPH

270 (W)

03/19/194 F-4 FTrace Trace 43.4 MPH63 MPH

300 (WNW)

03/18/193 F-6 F 0.03 in 0 in52.1 MPH82 MPH

280 (W)

03/17/192 F-6 F 0.07 in .5 in61.5 MPH110 MPH

270 (W)

03/16/1925 F2 F 0.24 in 2.3 in67.5 MPH97 MPH

280 (W)

03/15/1941 F25 F 0.04 inTrace 54 MPH105 MPH

250 (WSW)

03/14/1940 F17 F Trace in Trace in27.7 MPH75 MPH

200 (SSW)

View
03/13/1924 F11 F .07 in .8 in29 MPH52 MPH

290 (WNW)

03/12/1911 F-1 F 0.14 in 1.9 in65 MPH104 MPH

280 (W)

03/11/1917 F6 F 0.35 in 4.4 in77 MPH114 MPH

280 (W)

03/10/1925 F4 F .35 in 3.7 in47.2 MPH94 MPH

150 (SSE)

View
03/09/1919 F0 F 0 in 0 in36.1 MPH70 MPH

290 (WNW)

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 02/23/2019 at 7:03 AM.

Helon Hoffer
USDA Forest Service
White Mountain National Forest