Avalanche Forecast for Monday, February 4, 2019

This forecast was published 02/04/2019 at 7:02 AM.
A new forecast will be issued tomorrow.

The Mount Washington Avalanche Center will no longer issue daily avalanche forecasts for the 2018/19 season. Read more

The Mount Washington Avalanche Center will no longer issue daily avalanche forecasts for the 2018/19 season. Instead, we will post an updated General Bulletin as needed, in case of significant snow or weather events that might vary from the typical daily changes that come with spring weather. We will also keep you informed about the official closure of the portion of the Tuckerman Ravine Trail from Lunch Rocks through the Lip and Headwall as well as the switch from the Lion Head Winter Route to the summer trail. Observations from the field will continue to be a valuable resource, so please keep submitting photos, videos and observations here and we will do the same. Check the Forecast page for update on Sherburne Trail closures, which are imminent as spring snowmelt continues.

The switch to a General Bulletin does NOT mean that the mountains are now a safe place to ski. The hazards which emerge in the spring are significant and require careful assessment and strategic management. If you have never skied Tuckerman, peruse our Incidents and Accidents page for spring related incidents involving avalanches, long sliding falls, icefall, crevasse and moat falls, and other incidents related to diurnal changes in the snowpack. These will help you understand and plan for these hazards.


The Bottom Line

You could trigger small wind slabs that formed last night, while older and larger wind slabs on a smooth crust remain possible to trigger as well. Warming today combined with weight added from precipitation last night decreases the stability of these larger slabs which were slowly increasing in stability. Isolated terrain at lower elevations which received more rain may have the possibility of wet slab avalanches today as warming continues. The warming will also make our lower elevation snowpack less supportable and allow for deep postholing if you’re not on skis or snowshoes. All forecast areas have MODERATE avalanche danger today, with the Northern Gullies in Huntington Ravine being the one exception with LOW avalanche danger. While new wind slabs should exhibit obvious signs of instability, realize that the subtle decrease in instability due to warming and added weight from precipitation may be less obvious. It’s wise to continue minimizing the time you spend travelling on and below steep terrain with large wind slabs.

2019-2-4_printable_pdf

Danger Rating by Zone

Mountain Weather

The mercury rose to near the freezing mark late yesterday and into last night as we received mixed wintry precipitation. Snow was the primary precipitation type on the summit, where 1.4” was recorded with 0.26” of liquid precipitation (SWE). Our snow plots received around an inch of snow which transitioned to sleet and rain, producing a total of nearly 0.4” liquid precipitation (SWE). Temperatures continue to rise today and should ultimately remain above freezing in our terrain until tomorrow night. The current W summit wind of 60 mph should decrease to under 40 mph by this afternoon and increase to over 60 mph again tomorrow. Precipitation should be minimal today, falling as rain for all but the highest terrain. Rain tomorrow morning is forecast to transition to mixed wintry precipitation and maybe even snow by Tuesday night, with less than a tenth of an inch of water (SWE).

Primary Avalanche Problem – Wind Slab

Wind Slab

Aspect/Elevation

Likelihood

Size

Large wind slabs formed late last week can be found predominantly on the eastern half of the compass rose, where new and small wind slabs formed last night can also be found. The older slabs are stubborn but could produce a large avalanche, while the newer slabs will be more reactive to a human trigger. The isolated possibility may exist for a small, new slab avalanche to step down into a larger old slab. You may not find any new wind slab at lower elevations, but realize that precipitation overnight has added weight to the upper snowpack which helps keep human triggered avalanches possible today.

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

Wind slabs formed predominantly late last week sit above a melt/freeze crust which formed on January 25th. These slabs are quite large in east facing terrain, particularly in gullies that did not avalanche last week, like the Chute in Tuckerman Ravine, and their hard character makes them stubborn at best to a human trigger. Though bonding between slabs above the melt/freeze crust has improved, the prevalence of that smooth crust could combine with slab size to produce a large hard slab avalanche. West wind has built overnight snow into smaller wind slabs on the surface that will be more reactive to a human trigger. Wetter precipitation at lower elevations, possibly including the ravines, has added some weight to existing slabs. If you find yourself in terrain which received more rain than mixed precipitation last night, wet slabs may even be a concern. These factors, combined with continued warming today, essentially negate any strength gained in the snowpack yesterday.

Additional Concerns

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

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.

Snow Plot Information

DateHN24HN24W
(SWE)
Density (%)HSTTotalAir TT MaxT MinSkyPrecipComments
05/22/19
05:25
Trace 6.2 MMTrace60 CM0.5 C2.0 C-1.0 CClearNo precipitationView
05/21/19
05:25
0 CM 4.2 MM0CM60 CM2.0 C15.0 C2.0 COvercastNo precipitation
05/20/19
05:30
0 CM 20.4 MM0CM68 CM11.0 C12.0 C3.5 CObscuredNo precipitation
05/19/19
05:25
0 CM 0.0 MM0CM72 CM4.0 C6.0 C2.0 COvercastNo precipitation
05/18/19
05:20
0 CM 7.6 MM0CM80 CM1.0 C6.0 C1.0 COvercastNo precipitation

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
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)

05/18/1934 F26 F 0.06 in 0.5 in39 MPH74 MPH

300 (WNW)

05/17/1940 F28 F .22 in .05 in37 MPH81 MPH

300 (WNW)

05/16/1932 F25 F .03 in 04 in22.8 MPH40 MPH

310 (NW)

05/15/1926 F20 F .05 in .4 in32.1 MPH67 MPH

330 (NNW)

05/14/1928 F17 F .2 in 2 in19.1 MPH57 MPH

100 (E)

05/13/1928 F19 F .07 in 0.9 in34.6 MPH67 MPH

100 (E)

05/12/1931 F17 F 0 in 0 in20.5 MPH47 MPH

330 (NNW)

05/11/1932 F18 F .1 in 0 in53.6 MPH84 MPH

300 (WNW)

05/10/1944 F27 F .85 in 0 in50.1 MPH88 MPH

220 (SW)

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 02/04/2019 at 7:02 AM.

Ryan Matz, Snow Ranger
USDA Forest Service
White Mountain National Forest