A January thaw has begun and with it comes a trend toward instability in our snowpack. It is currently 45 F (7.2 C) at Hermit Lake and this warm air is expected to last until Wednesday. While rain showers are in the forecast, we aren't expecting significant rain until Wednesday. The main stability concerns during this duration aren't focused on people triggering avalanches as much as the weather causing natural avalanches. Recent weather has allowed the snowpack to consolidate and trend toward stability, however, this dramatic warm up will begin to tip the scale in the other direction toward instability in slabs that vary greatly from one location to the next. The reason is warm temperatures are breaking down bonds that exist in the slabs and creating freewater in the snowpack. As this freewater percolates down into the snow it creates more warming and melting. All of this water will continue to move down through the snow until it reaches a barrier. The most prominent barrier in our current snowpack is a pronounced rain crust that developed from our last rain event on Christmas Eve. Since that time we have had quite a lot of snow and a number of avalanche cycles that ran on or above this rain crust. As free water moves through the snow and reaches this layer it will start to flow down hill and lubricate the interface of the slab above and its bond with the rain crust below. This process could produce natural avalanches in our current snowpack. The rain crust isn't the only thing that can act as a barrier. Water ice and dense slabs can do the same thing. Generally speaking, thinner slabs will take less time to "cook" and therefore may have instabilities earlier than the thick slabs that you would find around the Bowl in Tuckerman. These thicker slabs have the potential to create larger avalanches but it will take more effort on the weather's part to get them to go. Our field observations found the rain crust to be at a wide variety of depths in the snowpack ranging from the surface to meters down below the surface.

The real trick to this is predicting if and when natural avalanche will occur. When we get rain introduced into cold slabs, the above process happens very quickly. Snow doesn't like rapid changes and will tend to avalanche under these conditions and we will often rate such events "High" avalanche danger. The weather event we are dealing with now is more subtle than a good soaking rain on cold slabs. Our previous instabilities had some opportunity to consolidate yesterday and this helped stability improve. While this rapid warm up is alarming, it isn't as dramatic as rain. We are going to have two days of warm and showery weather before the final exam on Wednesday when steady rain arrives. The extended duration of this weather may allow some areas to become quite stable while others produce avalanches. Expect the danger rating to remain at Considerable through the duration due to the possibility of natural avalanches.

There are a couple of other considerations worth mentioning. Expect falling ice to be a hazard over the next couple of days in both Ravines. I would also expect the Little Headwall to open up and have a substantial amount of running water making it an undesirable if not hazardous ski run.

Winter is scheduled to return to the mountains on Wednesday night as colder air moves in and changes rain to snow showers. A favorable upslope flow may allow for some accumulating snow in the mountains on Wednesday night. Another system will deliver precipitation on Friday. It looks like snow right now but it is a bit early to tell what is going to happen.

THE LION HEAD WINTER ROUTE IS OPEN. This is a steep and challenging route for mountaineers. Crampons, an ice axe and the ability to properly use this equipment are recommended for safe travel on this route. The John Sherburne Ski Trail has good snow cover all the way to Pinkham.