Posted 8:30 a.m., Monday, March 20, 2011
Tuckerman and Huntington Ravines have CONSIDERABLE avalanche danger. Natural avalanches are possible and human triggered avalanches are likely. The only exception to this rating is the Little Headwall which has Low avalanche danger. Natural and human triggered avalanches are unlikely.
Welcome Spring, and cheers to spring snowstorms! Let’s hope we have a lot more in the months to come…actually, let’s hope that this storm today pans out the way it’s forecasted to. I’ve learned the hard way that you’d better not count your inches before they fall. Current forecasts have snow beginning this morning and continuing into Tuesday. The heaviest precipitation will fall this afternoon; during this time winds will be from the south and increasing to 45-60mph (72-97kph). Total snow accumulations around 4-8″ (10-20cm) are expected during the day with another couple inches after dark.
Avalanche danger will be increasing throughout the day. Due to the S winds, areas with N-facing aspects will push into the Considerable range during the daylight hours, and will be nudging their way into High after dark. These N-facing aspects include the Escape Hatch, South Gully, and Odell Gully in Huntington and Hillman’s Highway and Left Gully in Tuckerman. Other areas with a more easterly aspect will follow closely behind as winds cross-load these slope with new slabs. The development of instabilities in these forecast areas will be slower than on S-facing slopes, but you shouldn’t underestimate the ability for cross-loading to occur. The human triggered avalanche in Pinnacle Gully on March 10 was an example of how southerly winds can create unstable slabs on E-facing slopes. Forecast areas facing mostly south, such as Lobster Claw, Right Gully, and North and Damnation Gullies will be the slowest to develop stability issues. Nevertheless, we expect these locations to develop enough instabilities by the end of the day to warrant a Considerable rating. To generalize all this, avalanche danger will be rising in all areas, but those facing N will be progressing most rapidly. The increasing trend will continue after dark as snow persists and winds wrap back around from the S to the NW. Expect avalanche danger tomorrow to remain elevated due to the NW winds.
Stability today will be also affected by the bed surfaces available for new snow to fall onto. In many areas this is a slick icy crust, while in other areas there are pockets of lighter density slab left over from 1″ of snow on Saturday morning. Neither of these potential bed surfaces will help stability, instead they generally make for very poor stability. In Right Gully and Lobster Claw, there will be a more textured bed surface that will help new snow stay on the slope, but once these textures are buried, all bets are off.
The John Sherburne Ski Trail has been very icy outside of the softening during midday hours. Expect a slick surface underneath any powder that falls today. If we get 10″ by tomorrow morning, I think the trail would become quite enjoyable, especially for the first motivated few to go down.
- Safe travel in avalanche terrain requires training and experience. This advisory 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.
- Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast. For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.
- This advisory expires at midnight. A new advisory will be issued tomorrow.
Jeff Lane, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713 TTY (603) 466-2856