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Blog: Forecast Addendum: Jan 14, 2016 - Weak layer outlook

Brett Kobernik
Forecaster, Website Coordinator

I like to ski and snowboard powder in avalanche terrain when appropriate. I also like to take my motorized snowbike into crazy terrain when I can. This is a big reason why I'm in the business I am. So, I pay close attention to things that clue me in to when getting into avalanche terrain is appropriate. Here are some current thoughts.

CURRENT SNOW SURFACE AS OF WEDNESDAY, JAN 13: In many locations, the snow surface has changed during over the last few days during the high pressure. There is also some surface hoar present. The surface snow from the last storm has changed into small grained faceted snow. This is a loose sugary type of grain that has the potential to act as a "persistent weak layer" as it gets buried. It is weak enough in many areas that we are sure to see some avalanche activity on it. In some areas it is weak enough that it won't hold much weight and will most likely avalanche before it allows a whole lot of snow to accumulate on top of it. In other areas, it is not so weak or there are wind and or sun crusts instead of weak facets. This situation is going to demand careful evaluation since conditions change from place to place.

OVERALL SNOWPACK STRUCTURE: In general, the old weak snow near the ground has improved and strengthened especially in areas with a deep snowcover. Shallow areas still have a poor snowpack structure. Enough so that they still demand my attention and I won't be trusting the shallow areas if we see a rapid big load on them.

AVALANCHE PATHS THAT RAN DURING THE CHRISTMAS STORM: After the natural avalanche cycle, slopes that avalanched were the safe bet. That is not necessarily going to hold true from here on out.

  • Some paths didn't clean out ALL of the old faceted sugary snow so it could avalanche again on the same weak snow near the ground
  • Snow that has fallen on top a number of the old bed surfaces has become weak due to the near surface facetingprocess. Weak snow on top of a firm bed surface could produce significant avalanches again once loaded up properly
  • Slopes that avalanched very early in the December cycle and filled back in immediately and now have a deeper overall depth are probably fairly stable. You will have had to follow a particularslope very carefully though to posses this information. Keep in mind that the surface snow is most likely weak anyway as described above.

CONCLUSIONS:

  • We've enjoyed a period of good stability and have been able to get into some steeper terrain. There are enough red flags out there now that we need to notch things back a bit as the next series of storms rolls through.
  • I'll be carefully monitoring the surface facets which are now getting buried. I'll be digging often and doing tests on them to try and figure out how sensitive they are and how widespread of a problem we have. This is my main concern as the storms add up.
  • Shallow snowpack locations will get due respect if it looks like they are going to get loaded up rapidly. It will take a fairly good amount of snow to make them reactive again but you can't dismiss them at this point.

Be careful out there during the next series of storms. Have a little patience and let the snowpack dictate what kind of terrain is appropriate.

Comments
<p>On point Kow... &nbsp; Weak surface snow is widespread, and now it&#39;s all about the slab development (or not). &nbsp;One of the most most difficult to forecast, dangerous, and tricky periods in any avalanche cycle occurs as the slab layer is developing. &nbsp;Toning it down while danger is rising seems obvious and an easy concept to convey. &nbsp; &nbsp; Perhaps, but it&#39;s difficult to break down the overconfidence wrought from high pressure powder &nbsp;and recent&nbsp;&quot;user friendly&quot; avalanche cycles, where naturals happen overnight and you can remote trigger bowls by just looking at them.</p> <p><br /> <img alt="" src="https://utahavalanchecenter.org/sites/default/files/images/avalanches/2015-16/IMG_7272.JPG" style="height:600px; width:800px" /><em>Not so user friendly, this New Years Eve avalanche failed on a thin persistent weak layer, similar to what is being buried by light snowfall in many areas today&nbsp;a week after the substantial pre-Christmas Storm. &nbsp;The slope that avalanched&nbsp;was recently ridden and had several sled tracks in it when the survivor triggered it,&nbsp;and the slide&nbsp;broke above him.&nbsp;</em></p>
Toby
Thu, 1/14/2016