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| 3.2.2009 |
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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, March 2, 2009 at 7:30 am.
City of Ketchum (www.ketchumfire.org) & the Friends of the Sawtooth Avalanche Center bring you this advisory.
Special Announcement:
An avalanche accident in western Wyoming resulted in three fatalities over the weekend. You can read the details of this and other avalanche incidents on the newly redesigned Avalanche.org website. Go to http://avalanche.org/ and click on Accidents.
Bottom Line:
Today the avalanche danger is estimated to be CONSIDERABLE in the North Valley, Salmon Headwaters and Sawtooth Mountains. Recent snowfall and wind have loaded weak layers buried 1 to 3 feet deep. These conditions resulted in a widespread natural and human-triggered avalanche cycle last Tuesday through Saturday. Although the stability appears to be improving, dangerous conditions still exist on many slopes and terrain steeper than 30 degrees should be carefully evaluated.
In the South and Central Valleys, the avalanche danger is estimated to be MODERATE. While a similar weak layer exists in this region, there has been less recent loading than in our northern mountains. Evaluate steep slopes carefully, and use extra caution on windloaded slopes.
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Danger by Aspect and Elevation:
Primary Avalanche Concern:
Last week’s series of storms tipped the balance on the Friday the 13th weak layers. Consisting of loose, sugary facets on shady aspects and an ugly multi-layer sandwich of crusts and facets on more sunny slopes, this layer is now buried 1 to 3 feet deep in much of our northern area. In the mountains closer to Ketchum and Hailey, this layer can be found about a foot down, except on wind loaded slopes where it may be more deeply buried.
In our northern mountains, natural or human-triggered avalanches were reported five days in a row – from last Tuesday through Saturday. Yesterday was the first day that no new slides were reported. In Baker Creek yesterday, I saw numerous natural avalanches that probably released last Thursday or Friday, and one slide that was triggered on Saturday (see photos below). While snowpit tests are starting to show improving stability, several groups in the North Valley still reported collapsing yesterday, and some of these were the large, rumbling variety.
Although we began with widespread instability after last week’s storm, as the snowpack begins to stabilize it becomes more variable by nature. Unfortunately the strengthening process does not occur at the same pace on all slopes. It’s best to maintain a healthy dose of skepticism, and don’t let yourself get convinced by one piece of evidence pointing to improving conditions. I know there are still slopes where you could trigger a slide, and by carefully evaluating terrain steeper than 30 degrees, you stand a good chance of avoiding those spots. Dig a quick snowpit to look for clean and/or easy shears within the top 2-3 feet of the snowpack, and pay attention to obvious clues such as collapsing and cracking. The greatest danger remains on mid to upper elevation slopes in our northern mountains, especially those with additional drifting from recent winds.
In the South and Central Valley, unstable slopes are more isolated, but you’ll still want to use caution in steep terrain and on any windloaded slope. Skiers in the South Valley yesterday received a collapse and shooting cracks on a dense wind slab that was sitting on faceted snow. They wisely chose to avoid the wind loaded area and were able to safely enter the slope lower down.
Current Conditions:
With a bit more sunshine than expected, yesterday’s temperatures exceeded forecasts, especially in the valley where they were a good 5-10 degrees higher. Highs in the mountains climbed into the upper 30s and even the 40s in some warmer locations. Ridgeline winds calmed by mid morning and were fairly light until they increased again in the afternoon.
Warm temperatures took their toll on the snow surface conditions, especially at mid and low elevations where moist snow could be found on all aspects. Upper elevation, northerly aspects are still holding soft, dry snow.
This morning, temperatures are in the low 30s at most elevations. Southerly winds increased significantly overnight in our northern area, where they averaged 20-30 mph with gusts into the 40s.
Mountain Weather Forecast:
A warm and moist southwesterly flow will continue to impact the region today, bringing more balmy temps and some precipitation by tonight. This should be in the solid form above the valley floor, but we may see some rain at lower elevations. By tomorrow morning, our mountains could see 2-4 inches of new snow accompanied by strong gusty winds. Temperatures should reach the mid to upper 30s today at higher elevations, and a high in the upper 40s is forecasted for the valley. Southerly winds should blow 10-20 mph along upper elevation ridgelines, but periods of stronger winds are possible, especially tonight.
Photos:
1. Triggered slide in Apollo Creek
2. Natural avalanches in Apollo Creek
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| Reported Conditions |
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| Temperatures |
| Overnight Low |
30 |
32 |
29 |
| 6am Temperature |
32 |
33 |
30 |
| 24 hr Maximum |
36 |
38 |
50 |
| Winds |
| Note: Increased overnight in our norther mountains |
| Current Winds |
27 S |
12 SSE |
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| 24 hr Average |
17 S |
9 SSE |
- |
| Maximum Gust |
47 SSE |
36 SSW |
- |
| Snow - Storm Interval # 19 |
| Total Depth |
55" |
48" |
26" |
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