Snow & Avalanche Weekly Summary
Surface conditions were improved in the Summit area last Wednesday by the addition of 6" of new snow. However, due to warming and the skies clearing after the storm the snow quickly changed becoming heavy on solar aspects. As overnight temperatures dropped a melt-freeze crust formed on these slopes. Overall the new snow appears to be bonding decently well to a variety of old surfaces. The generally poor snowpack structure in Summit area should not be forgotten. Just after the storm ended on Thursday several natural slab avalanches were spotted by observers. As the storm tapered off, winds shifted from the southeast to the north, building slightly thicker slabs on a variety of westerly aspects. Areas adjacent to cross loaded and stripped ridges will be particularly suspect for triggering an avalanche 1-2' thick.
The real headline this weekend is WARMING! A series of low pressure systems are pulling warm air into the region, and ridgetop temperatures will climb well above freezing by Saturday afternoon, with valley bottoms potentially getting into the upper 40's F. More on this below in the Mountain Weather section. Warming can initiate wet loose avalanches in steep terrain, and may make slab avalanches (especially on persistent weak layers) easier to trigger. Warming will likely not just be limited to solar aspects during a weather event like this. Avoid being in the runout of steep slopes when things start to warm up.
This report is a weekly summary, so PLEASE be sure to follow the Turnagain Pass advisory for current weather and avalanche conditions. Help us keep tabs on the Summit area and if you see any avalanche activity send us an observation HERE. Thank you to everyone who has already submitted observations this season - you can see those HERE!
Above freeze temperatures at ridgetops combined with clearing skies could rapidly warm the snowpack on all aspects by Saturday afternoon. Small to large wet loose avalanches may occur naturally in steep terrain, particularly on solar aspects and in rocky areas. These avalanches can entrain a lot of snow and run farther than expected. Even a relatively small wet loose avalanche could have high consequences by knocking you off your feet in steep terrain, or bury you deeply in a terrain trap. Wet loose avalanches can also be a trigger for larger, much more destructive slab avalanches. Pay attention to surface crusts becoming soft and not supportable. Rollerballs coming off of rocks and sinking into wet, unsupportable snow are signs that the snow is reaching the tipping point to slide.
If temperatures stay elevated throughout the week, particularly if it does not refreeze at night for several nights at upper elevations or it rains, there could be the potential for wet slab avalanches. Wet slab avalanches are typically large and destructive, entrain large amounts of snow, and often break to the ground.
Cornices: Large cornices are looming over many ridgelines in the Summit area. Warming may make cornices break off more easily. Even a small block of cornice can easily injure or kill a person. It's best to give these sleeping giants a wide berth.
Wet loose avalanches that slid when the sun came out on Thursday afternoon.
Cornices are hanging precariously over many ridgelines in the Summit area. The best way to manage cornices is to avoid them.
This melt-freeze crust at 2500' formed on east aspects with only a few hours of warming from the sun on Thursday. This weekend is expected to be much warmer.
It has been nearly a month since the last human triggered avalanche was reported in the Summit area. However, observers continue to easily find two well documented layers of weak snow from January 2-3' deep in the snowpack. These layers appear to be dormant for the time being and are generally non-reactive in stability tests, but as long as this structure exists, there will always some possibility of triggering a large, dangerous avalanche. As we round the corner into spring, it will be important to keep these layers in mind. There are two things that could wake them back up: a rapid loading event, particularly rain, and warming. This type of avalanche problem will likely not give any feedback such as cracking, collapsing, or "whumphing", and it could be the 10th person to ski a slope that finds the right spot to trigger an avalanche. Always consider the consequences of slopes that you choose to ski or ride, avoid terrain traps, and continue to practice safe travel techniques by only exposing one person at a time a hazard.
Two well-documented weak layers from January can easily be found in pits. They are dormant for the time being, but rapid loading or warming could wake them back up.
At elevations below 2000' the snowpack is extremely thin and has a very weak structure. In this pit, weak facets at the ground would not even support compression test columns under their own weight, and propagated fractures with easy force.
Last week in Summit saw mostly pleasant weather, with ridgetop temperatures in the teens and 20's F, and daily swings in valley bottoms from teens and 20's F overnight to highs in the mid-to-upper 30's F. Ridgetop winds were moderate from the northeast during the beginning of the week. A storm on Wednesday brought 6" of new snow (0.6" SWE) to the Summit area. The temperature remained below freezing during the storm. The majority of the precipitation arrived with moderate southwest winds, but as the storm tapered, winds increased slightly and pulled back around to the north. On Thursday afternoon skies cleared and temperatures at 1400' quickly shot back up to the upper 30's F by late afternoon.
Warm air aloft is being pulled north by a series of low pressure systems marching across the north Pacific and the Gulf of Alaska. From the National Weather Service:
"The big story for the weekend will be temperatures. Cloud-free sky and 850mb temperatures above zero should yield the warmest temperatures of the year for most areas of Southcentral Alaska. Solid 40s are a good bet while this forecaster believes a few places will hit 50 degrees Saturday and/or Sunday. Spring has sprung."
850mb means ridgetop elevations, so expect ridgetop temps to get well above freezing by Saturday afternoon, and possibly into the low 40's. Temperatures will continue to be elevated on Sunday. Winds may get gusty as these lows move by. Most of the activity is expected to stay to the south of us, but some scattered snow and rain showers will likely reach the periphery of the Gulf of Alaska throughout the upcoming week.
Stay tuned to the CNFAIC weather page for an updated weather forecast each day. The best way to keep an eye on temperatures at Summit Lake is to look at the RWIS webcam snow stake HERE and the NRCS Snotel site HERE. *The above MP 45 station is the best ridge top temperature information. This weather station is in a sheltered area and wind data is typically less than the actual ridgetop winds. Also look at Sunburst Weather Station in Turnagain for a comparison.
This is a general backcountry avalanche advisory issued for Summit Lake Area as the core advisory area(this advisory does not apply to highways, railroads, or operating ski areas).
Riding status is not associated with avalanche danger. An area will be open to motorized use in accordance to the Forest Management Plan when snow coverage is adequate to protect underlying vegetation. Backcountry hazards including avalanche hazard are always present regardless of the open status of motorized use areas.
(Updated: Apr 20, 2018 )
|AREA||STATUS||WEATHER AND RIDING CONDITIONS|
|Johnson Pass:||Closed||Closed as of April 20|
|Placer River:||Closed||Closed as of April 17th|
|Skookum Drainage:||Closed||Closed as of April 1st.|
|Twentymile:||Closed||Closed as of April 13th|
|Lost Lake Trail:||Closed||Closed as of April 13th|
|Primrose Trail:||Closed||Closed as of April 13th|
|Resurrection Pass Trail:||Closed||Closed as of April 20th|
|South Fork Snow River Corridor:||Closed||Closed as of April 13th|
|Summit Lake:||Closed||Closed as of April 20th|
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