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| 12.24.2007 |
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This is Chris Lundy of the Sawtooth National Forest Avalanche Center with your Backcountry Avalanche Advisory and Weather Forecast for Monday, December 24, 2007 at 7:30 am.
City of Ketchum (www.ketchumfire.org) & the Friends of the Sawtooth Avalanche Center bring you this advisory.
Special Announcement:
Now that there is enough snow, we hope to have the Avalanche Rescue Training Park installed by the end of the day in the field next to the new Catholic Church on Sun Valley Road. This will be a great way to try out the new beacon that you get for Christmas! All that is needed to practice your avalanche rescue skills is an avalanche beacon and probe.
Bottom Line:
Today the avalanche danger is estimated to be generally MODERATE. However CONSIDERABLE danger remains in steep, rocky terrain, or on wind loaded slopes.
Weak, faceted snow is buried 1-2 feet deep throughout our area. This layering was responsible for a natural avalanche cycle late last week and for a human triggered slide on Saturday. Snowpit tests are showing improving stability, but weaker areas exist where you could still trigger a slide. These will most likely be found in steep and/or rocky terrain. Warming temperatures overnight may compound the problem today by increasing the stress on the snowpack.
Strong winds from late last week have created thick wind drifts along exposed ridgelines. Additional wind loading will likely take place today with new snowfall and stronger winds in the forecast.
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Primary Avalanche Concern:
I was at the head of Baker Creek yesterday where I saw evidence of a significant natural avalanche cycle that occurred late last week. Yesterday we received a report that two skiers triggered a slide in the Newman drainage, a tributary of Baker Creek (see photo below). While ascending lower angled terrain, they felt a collapse and turned to see the adjacent slope avalanching. The upper portion of the slide appears to have run within the recent storm snow, but down slope it fractured lower into the underlying faceted snow.
Stability tests are showing that the facet layer 1-2 feet deep is gaining strength. Many slopes appear to be stable which has lead to the generally Moderate danger rating. Still, the nature of our current snowpack problem almost guarantees there are still slopes where you could trigger a slide. If you find one of these areas, the Moderate danger rating won’t mean much to you. The terrain that remains the most suspect are very steep slopes and rockier terrain, where weaker snow exists and instabilities tend to last longer. Also avoid wind loaded slopes where there is a greater load sitting atop the facets.
Temperatures overnight have climbed higher than they have in over a week. Significant warming can poke a finger in the eye of a faceted snowpack, adding additional stress to an already stressful situation. Yet another reason to remain conservative with your terrain choices today.
Secondary Avalanche Concern:
Strong winds from late last week have created thick wind deposits along many upper elevation leeward ridgelines. In many places these wind slabs are sitting atop weak faceted snow, and I experienced several collapses near ridge crests yesterday. New snow and strong westerly winds are in the forecast, so expect the formation of fresh wind drifts during the day today. These newer drifts by themselves will likely be relatively small, but if they step down into deeper wind slabs the potential exists to trigger a sizeable avalanche.
Current Conditions:
Some of you must have been bad boys and girls because Santa doesn’t seem to be delivering the early Christmas present he promised. Snowfall overnight was well below forecasted amounts, with most areas only receiving 1-2 inches. Our far northern area may have picked up a few inches more. Overnight, mountain temperatures climbed significantly and are currently in the upper 20s. Ridgeline winds are currently blowing 15-25 mph from the southwest.
Mountain Weather Forecast:
While the storm currently affecting our area isn’t producing as much as expected, we should still pick up 2-4 inches of new snow by this evening. A cold front will move through the region this afternoon, dropping temperatures and bringing gusty winds.
Mountain temperatures should remain in the mid to upper 20s early today before dropping into the teens later this afternoon. The forecasted valley high is around 28 degrees. Ridgeline winds are expected to blow 20-30 mph from the southwest shifting to the northwest later today.
Photos:
1. Triggered Slide in Newman Creek
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| Reported Conditions |
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| Temperatures |
| Overnight Low |
23 |
23 |
21 |
| 6am Temperature |
26 |
26 |
23 |
| 24 hr Maximum |
27 |
29 |
26 |
| Winds |
| Current Winds |
15 SW |
6 SW |
- |
| 24 hr Average |
13 W |
12 W |
- |
| Maximum Gust |
30 W |
38 NW |
- |
| Snow - Storm # 6 |
| New Snow |
1-2" |
1" |
1" |
| Total Depth |
41" |
29" |
16" |
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