Yesterday forecasters observed numerous natural and human triggered dry loose slides on steep, northerly facing slopes. While these slides were all relatively small and manageable, many of them had entrained enough snow on the way down the slope that you would not want to be caught in them.
A party earlier this week reported triggering a small but energetic slide on a wind-loaded NE facing slope off of 4068. Forecasters observed some similar natural activity below Hatch peak. While the winds have been light and temperatures mild, these slides are a reminder that small, localized instabilities remain on upper elevation terrain.
Earlier this week, warm temperatures, high humidity, and periods of sun encouraged both natural and human triggered wet loose activity.
Between Tuesday and Thursday Hatcher Pass picked up about 5-7’’ of light density snow, mostly at upper elevations. This snow was affected by periods of warm temperature, high humidity, and some direct sunlight, causing it to settle out, initiate some wet loose activity, and form a crust on steep solar aspects.
Thursday night’s cold, clear conditions helped radiate out some of the moisture in the snow surface and many parties were finding soft dry turns on all aspects on Friday. Even though the sun was out, a light breeze and relatively cool temperatures helped keep the snow surface from getting too wet. That said, steep solar slopes were being warmed and may have a thin crust on them going into this next period of snow.
As they say, today’s snow surface is tomorrow’s weak layer. The most important part of this forecast is likely understanding what kind of surface this weekend’s snow will be falling on. Our recent low density and recrystalized snow surface will likely prove to be an easy weak layer for more dry loose or storm slab activity to fail on as new snow starts to accumulate.
|Signal Word||Size (D scale)||Simple Descriptor|
|Small||1||Unlikely to bury a person|
|Large||2||Can bury a person|
|Very Large||3||Can destroy a house|
|Historic||4 & 5||Can destroy part or all of a village|
The biggest hazard going into the weekend will continue to be the potential for triggering small dry loose avalanches in steep terrain, mostly on the north half of the compass. These slides will likely be 4-6’’ deep and could run several hundred feet where slopes have a sustained angle above 40°.
Recent snow was relatively light density, good on some moisture, and has since dried out and recrystalized after Thursday’s cold, clear night. We observed numerous sluffs point releasing from steep rocks, cornices, and from skier traffic. While these slides had no propensity for propagation, many of them are were running to where the slope transitioned and entraining all the new snow as they went.
Be aware that the surfaces these sluffs are running on may change their speed and behavior and make them a little more difficult to deal with. When you’re on the slope, allow sluffs to run in front of you or move to the side to get out of the way. Remember that as new snow accumulates this weekend, these slides will likely become more deep and energetic.
Independence Mine Snotel reported picking up 5-7’’ of snow at about 1/2’’ of snow water equivalent between Tuesday and Thursday. On Tuesday and Wednesday, this snow was affected by periods of warm temperatures, high humidity, and strong sun causing it to settle out considerably. Clear, cold conditions on Thursday night dried it back out a bit again and there’s now loose, cold snow on most aspects.
Although winds have remained light, small, localized wind effects can be found on upper elevation ridgelines.
It’s currently snowing up at Hatcher Pas and this weekend looks like a return to active weather with a couple of inverted troughs bringing precip in from the east/southeast. Accumulations look modest with an inch or so expected Saturday and 2-4’’ possible mostly early am Sunday. Winds look to remain light but will shift to the North by the end of the weekend.
NWS AVG Forecast here.
NWS point forecast here.
Marmot Weather Station here.
Independence Mine Snotel here.
Frostbite Bottom Snotel here.
State Parks Snow Report and Motorized Access information here.
XC trail grooming report for Mat-Su, Anchorage, and Kenai here.