| Posted: 7:56 a.m., Saturday, March 10, 2007 |
Huntington Ravine currently has LOW avalanche danger. Natural avalanches are very unlikely and human triggered avalanches are unlikely except in isolated pockets. Normal caution is advised.
It is a bright and balmy morning here at Hermit Lake. The current temperature is 41 F (5 c) which, after last week, feels like a Bermuda get-a-way to me. The valleys are still chilly and we expect some of that air to mix with ours today as SW winds increase through the day. Clouds will also increase through the day and we can expect precipitation to arrive this afternoon and last until around midnight. This weather maker will be the focus of today's stability issues. The forecast is calling for a total of .51" (1.3 cm) of liquid from this event with the majority of that forecasted to come in after 6 pm. It is expected to start out as a mix of snow and frozen mixed precipitation before transitioning to a period of rain. Cold air will move back in tonight and change the precipitation back to snow leaving the mountain with light accumulation. If this plays out as suggested, increasing avalanche danger associated with rain on slabs will be limited to the later evening hours. However, I can't ignore the current thermometer reading. If the precipitation starts as rain, I will become concerned about the potential for natural avalanche activity in some areas, mostly in Tuckerman Ravine. Keep a close eye on precipitation type and intensity and expect increasing avalanche danger with the onset of rain. Rain will weaken the bonds developed in the slabs and add weight and therefore additional stress on the weak layer. If it is able to get all the way to the faceted layers it will weaken them even more and ultimately act as a lubricant on the bed surface. In other words, rain has the ability to create natural avalanche activity.
As for current stability issues, the primary area of concern is the Lip and areas immediately around it that extend just under the Headwall. Yesterday skiers got into a lot of our terrain including the Lip, Sluice and Chute without incident. However, our stability tests on the north side of the Ravine found lots of faceted weak layers underneath slabs. In some places these were barely developed and in others the layer of facets was a foot thick. These developed during last week's very cold snap and in most areas can be found just above a thin crust. The slabs above these weak layers vary in density and apparently the bridging strength is good based on the ski tracks in the Lip. That alone is not enough to drop this area to Low as we are still concerned about the possibility of you or a group of you triggering a slide in this area. Other locations harbor similar stability issues, like Right Gully and in pockets of the Sluice and Bowl. These are also the areas that I am most concerned about if we end up seeing all rain on our snow today.
The Lion Head Winter Route is open. This is a steep and challenging route. Crampons, an ice axe, and the ability to properly use this equipment are necessary for safe travel on this route. The John Sherburne Ski Trail is open with top to bottom coverage.
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Avalanche Advisory Archives.
United States Avalanche Danger Descriptions.
Échelle Canadienne de risque d’avalanche.
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