General Bulletin for Monday, December 30, 2019

This information was published 12/30/2019 at 7:18 AM.
A new bulletin will be issued when conditions warrant.


The Bottom Line

A storm system will impact the forecast area over the next 24 to 36 hours bringing up to 13” of snow before tapering off Thursday morning. Wind and new snow will combine to form new wind slabs capable of producing avalanches. The size and chance of triggering avalanches will increase as the snow continues to fall over the next few days. Continued, poor visibility will make identifying these new slabs challenging so be conservative with terrain choices until the weather settles later in the week.

2019-12-30-General-Bulletin-Printable

Danger Rating

The summer Lion Head Trail remains the safer choice for accessing the summit of Mount Washington from the east. The Winter Lion Head Route still needs more snow. An ice axe and crampons are needed near treeline and above with micro-spikes useful on trails below.

General Bulletins are issued when unstable snow may exist within our forecast areas but before conditions warrant or available resources allow 5-scale avalanche forecasts. Thank-you to everyone who has submitted observations! We will start 5-scale forecasts on Wednesday, January 15 or earlier, if possible. Please remember that avalanches can and do occur before 5-scale avalanche forecasts are issued.

Mountain Weather

A storm system will bring much needed snow to the range over the next 48 hours and continued snow showers through Wednesday. Both the NWS and the OBS are in agreement that a foot or more new snow is possible at the upper elevations, with the chance of mixed precipitation at higher elevations for a brief period on Tuesday afternoon as milder air wraps into the area. Temperatures will be in the teens to lower 20s F with wind from the SE at 25-60 mph through the storm period and as the low pressure pulls away Tuesday evening seasonably colder air will return with increasing winds from the west. For travelers above treeline, expect blowing snow creating near white out conditions making navigating difficult.

Forecast Discussion

From field observations (thank you) we believe that the 4.4mm of liquid that fell on Friday the 27th penetrated into the snow surface before temperatures dropped on the 28th creating a snow surface more closely resembling textured foam than solid water ice. This textured surface will be conducive to bonding for the new snow expected over the next few days. With wind forecast light to moderate over the next few days, drifted snow will likely be found higher up in the terrain, helping to fill start zones & covering more bushes. In the short term, this will present the potential for sensitive new wind slabs to be found closer to ridge tops than we’ve had this season, and in the long term create a larger, wider bed surface for the next avalanche cycle.

Another hopeful point is that this new snow should put us back on track to fill in our snowpack. Looking at the numbers, the average snow total for December on the summit of Mount Washington is 45.5”. As of this morning we are at 37” so if we get 12” before the end of the day Tuesday we will be above average for the month of December. Let’s hope we finish out the year above average!

Additional Information

Conditions on the Sherburne ski trail should improve after this new snow.

There will be an avalanche awareness talk at 5:30-7:30pm, Thursday, January 2nd at Bissell Brothers in Portland. Come on down for a chat and a brew!

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
04/13/20
06:15
0 CM 0.1 MM0CM206 CM-3.5 C7.5 C-7.0 COvercastRain
04/12/20
06:20
Trace 1.8 MMTrace216 CM-7.0 C-4.0 C-7.0 CFewNo precipitation
04/11/20
06:20
14 CM 23.1 MM 14%62CM222 CM-8.0 C-6.0 C-8.0 COvercastNo precipitation
04/10/20
06:30
53 CM 49.5 MM 12%NC200 CM-6.0 C-2.0 C-6.5 COvercastSnowView
04/09/20
06:25
0 CM 0.0 MM0CM158 CM-1.0 C8.0 C-4.5 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
05/25/2054 F46 F 0.0 in 0.0 in18.7 MPH44 MPH

260 (W)

05/24/2054 F40 F 8.3 in 21 in8.3 MPH21 MPH

280 (W)

05/23/2055 F43 F 0.0 in 0.0 in15 MPH45 MPH

300 (WNW)

05/22/2055 F40 F 0.0 in 0.0 in37.4 MPH67 MPH

290 (WNW)

05/21/2053 F38 F 0.0 in 0.0 in29.4 MPH59 MPH

280 (W)

05/20/2050 F34 F 0.0 in 0.0 in29.4 MPH59 MPH

280 (W)

05/19/2041 F27 F 0.0 in 0.0 in15.3 MPH36 MPH

100 (E)

05/19/2050 F34 F 0.0 in 0.0 in11.4 MPH25 MPH

30 (NNE)

05/18/2045 F30 F 0.0 in 0.0 in14.7 MPH36 MPH

70 (ENE)

05/17/2040 F30 F 0.0 in 0.0 in17 MPH35 MPH

270 (W)

05/16/2037 F28 F .16 in 0.0 in38.8 MPH101 MPH

310 (NW)

05/15/2042 F32 F .95 inTrace 31.5 MPH95 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 12/30/2019 at 7:18 AM.

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