Avalanche Forecast for Saturday, March 23, 2019

This forecast was published 03/23/2019 at 7:06 AM.
A new forecast will be issued tomorrow.

NOT THE CURRENT FORECAST

This is an archived avalanche forecast and expired on 03/23/2019 at midnight.


The Bottom Line

Dangerous avalanche conditions exist today with large, natural avalanches becoming likely. Fifteen to eighteen inches of new snow combined with loading wind speeds from the northwest are creating wind slabs that are capable of producing very large natural avalanches. Avalanche danger for the Presidential Range is HIGH today. Travel in avalanche terrain is not recommended. The exceptions are the Northern Gullies in Huntington and the Right Side of Tuckerman which have CONSIDERABLE danger. Protected areas and lower elevations harbor softer storm slabs that are likely to be sensitive to a human-trigger.

Printable 2019-03-23

Forecast Area

The USDA Forest Service Mount Washington Avalanche Center has issued a backcountry avalanche warning for the Presidential Range.  Avalanche warning criteria may also be met in other areas outside those forecast by the avalanche center. This avalanche watch does not apply to operating ski areas.

Avalanche danger will increase through Saturday, March 23, 2019, with very dangerous avalanche conditions on and below slopes steeper than 30 degrees. Natural avalanches will be likely. Travel in avalanche terrain is not recommended.

Avalanche Safety Information Study

Please contribute to the effort to improve backcountry avalanche forecasts! Researchers in Canada devised a study 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.

Mountain Weather

Yesterday’s nor’easter delivered 1.1” of water to the Presidential Range. This fell as snow at mid and upper elevations with just over 15” landing on the summit (6288’) and at Hermit Lake (3800’) and 18” at Grey Knob (4370’). The first half of snowfall arrived on wind that started from the SE and then shifted to NE in the 30-45 mph range. Wind speeds slowed significantly around dark and then quickly ramped to 50 mph from the NW. The bulk of the storm has passed, though higher elevations will see another 2-4” of snow this morning. Wind will remain from the NW in the 70-90 mph range for the day as skies begin to clear later. Wind will shift toward the west tomorrow and drop slightly with a chance of snow.

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

The bullseye data for growing natural avalanche danger is heavy snowfall yesterday accompanied by increasing wind today. Wind from the NW today will load east-facing slopes, increasing the load in steep terrain and stressing weak layers below. These wind slabs will likely be reactive to triggers due to the lower than forecast overnight wind speed. As this load increases and stresses the upside-down nature of the snowpack, instability will peak and large natural avalanches will become likely.

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.

Secondary Avalanche Problem – Storm Slab

Storm Slab

Aspect/Elevation

Likelihood

Size

Lower than expected wind speed has likely left some snow with little wind-effect. These storm slabs may appear soft, but will have an upside-down structure and may be touchy to human triggers. With storm totals so far up to 18” in some locations, an avalanche in this snow will easily be large enough to bury a person.

What is a Storm Slab Avalanche?

  Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Today’s stability concerns today are located within the new snow that fell yesterday. This snow fell on a mix of icy melt/freeze crust and firm wind slab, both of which will act as a hard bed surface for today’s avalanche cycle. Periods of moderate to light wind speeds yesterday have created  several soft layers that will act as weak layers today. The upside-down structure of the snowpack will be amplified today as strong wind from the NW continues to load easterly aspects. While the forecast wind speed will eventually increase stability with bridging strength, we will pass through peak instability today with some terrain capable of producing very large, natural avalanches. Travel in avalanche terrain is not recommended today. Local ski trails and glades will offer great alternatives to risking it in steep terrain.

Additional Concerns

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
04/24/19
05:20
0 CM 1.7 MM0CM146 CM4.5 C7.0 C2.0 COvercastNo precipitation
04/23/19
05:22
0 CM 10.4 MM0CM152 CM3.0 C12.0 C1.0 COvercastRain
04/22/19
05:20
0 CM 0.0 MM0CM156 CM1.0 C10.0 C1.0 CFewNo precipitation
04/21/19
05:15
0 CM 28.0 MM0CM160 CM6.5 C11.0 C6.5 CBrokenNo precipitation
04/20/19
05:15
0 CM 16.5 MM0CM175 CM9.5 C12.0 C6.5 COvercastRain

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
04/23/1946 F33 F .18 in 0.0 in25.8 MPH60 MPH

240 (WSW)

04/22/1942 F33 F .15 in 0.0 in18.1 MPH54 MPH

50 (NE)

04/21/1945 F36 F 0.21 in 0 in23.8 MPH66 MPH

170 (S)

04/20/1949 F43 F 1.11 in 0 in42.6 MPH96 MPH

240 (WSW)

04/19/1947 F41 F 0.23 in 0 in46 MPH95 MPH

240 (WSW)

04/18/1942 F18 F .23 in .2 in39.4 MPH98 MPH

240 (WSW)

04/17/1925 F15 F 0 in 0 in28.8 MPH82 MPH

330 (NNW)

04/16/1916 F12 F .28 in 1.5 in82.2 MPH142 MPH

290 (WNW)

04/15/1945 F12 F .97 in 1.6 in55.6 MPH133 MPH

290 (WNW)

04/14/1945 F24 F 0.22 in 0 in53 MPH85 MPH

290 (WNW)

04/13/1941 F28 F 0.09 in 0 in55.8 MPH86 MPH

280 (W)

04/12/1941 F20 F 0.15 in 0.0 in47 MPH106 MPH

240 (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 03/23/2019 at 7:06 AM.

Helon Hoffer
USDA Forest Service
White Mountain National Forest