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| 2.25.2009 |
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This is Chris Lundy of the Sawtooth National Forest Avalanche Center with your Backcountry Avalanche Advisory and Weather Forecast for Wednesday, February 25, 2009 at 7:30 am.
Blaine County Search and Rescue & the Friends of the Sawtooth Avalanche Center bring you this advisory.
Special Announcement:
The Idaho Department of Parks and Recreation will be teaching an avalanche basics class for snowmobilers this Friday evening and Saturday in Fairfield. Friday evening is a classroom lecture, and we will be assisting them during a field session on Saturday. Check out their website http://parksandrecreation.idaho.gov/recreation/snowmobileeducation.aspx for more information. Sign up is required, contact Lance Robinson at (208) 514-2413 or lrobinson@idpr.idaho.gov.
Bottom Line:
Today the avalanche danger is estimated to be CONSIDERABLE on mid to upper elevation slopes, especially if recently wind loaded. Recent snowfall combined with wind has buried a weak layer of facets 8 to 16 inches deep. Many signs of instability were observed yesterday, including triggered avalanches, collapsing of the snowpack, and poor stability test scores. The greatest danger exists on wind loaded slopes, easterly and southeasterly aspects, and areas that received the greatest snowfall from this last storm – including the head of Baker Creek, the Salmon Headwaters, and Sawtooth Mountains.
Although the valley received a good freeze overnight, wet slides will likely become a concern today as warm temperatures melt the thin surface crust.
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Danger by Aspect and Elevation:
Primary Avalanche Concern:
We’re smack dab in the middle of the classic instability problem for which our area is notorious. A long dry spell forms a nasty weak layer, and then we load it with a little snow, and then a bit more snow, and then…we stop just shy of getting enough load to cause widespread instability. Our snowpack is left hanging in a tenuous state of confusion where it can’t quite decide to whether to hold onto the slab or let it fly down the hill. This is a tricky situation for us backcountry recreationalists to evaluate, because the line between a stable and unstable slope is a fine one.
Yesterday I was on Butterfield, and my observations there jived with reports from Galena Summit. On a shady aspect, I didn’t get any clean shears in snowpits, although a layer of loose, cohesionless facets were easily identified about 12-16 inches deep. On east and southeast facing slopes, it was a different story. A particularly nasty breed of weak layer, the dreaded facets atop a crust, was found buried about 10-12 inches deep and produced very easy and clean shears. Check out this video: http://www.youtube.com/watch?v=_aJuEAKLm9g . We experienced collapsing on southeast aspects, as did skiers on Galena Summit and in the Sawtooths.
On our descent, I ski cut the top of a windloaded, east facing slope and released an avalanche 200 feet wide and 10-16” deep that ran on the facet/crust layer. You can see a video of the aftermath here: http://www.youtube.com/watch?v=qNs4YLEs8gc and check out the photos below. We also received a report of a skier in the Sawtooths releasing a decent-sized avalanche from a ski cut on a wind loaded slope.
So clearly there is some significant instability out there, the trouble is that it’s not widespread. Dust off your avalanche shovel – or you can even use your hand – and dig down to see what you’re dealing with. Look for clean and easy shears within the top 2 feet of the snowpack. The greatest danger exists on wind loaded slopes, easterly and southeasterly aspects, and places within our region that got the most snow from the recent storm – the head of Baker Creek, the Salmon Headwaters, and the Sawtooth Mountains. I am almost certain that avalanches could be triggered in the sub-drainages of Baker Creek, such as Apollo and Brodie, and in the Salmon Headwaters where very similar conditions exist to what I experienced yesterday.
Current Conditions:
A fast and furious bout of precipitation yesterday morning dropped another 2-4 inches of new snow at mid to upper elevations, and then intermittent snow showers continued through the day. Storm totals since last Sunday are about 10-16 inches of dense new snow, with the most falling in the Salmon Headwaters where 1.6” of water weight was recorded. Most of our region received about .75-1” of water.
Westerly winds continued to blow strongly though the day yesterday, averaging 20-30 mph on Titus with gusts into the 50s and 30-40 mph in the Soldier Mountains gusting into the 70s. They’ve decreased overnight and are currently blowing 5-15 mph from the southwest. Temperatures this morning are in the upper teens to low 20s at all elevations.
Mountain Weather Forecast:
Unsettled weather will continue today as another weak system moves through the area. Expect increasing clouds with a chance of snow by this afternoon. By tomorrow morning, we could squeeze out 1-3 inches of new snow before a stronger system moves into our region. Ridgeline winds are forecasted to increase during the day, averaging 15-25 mph from the southwest to west at 10,000 feet. Mountain temperatures should reach the mid 20s to low 30s, and the valley should climb into the low 40s.
Photos:
1. Butterfield Avalanche
2. Butterfield Avalanche
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| Reported Conditions |
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| Temperatures |
| Overnight Low |
17 |
22 |
23 |
| 6am Temperature |
18 |
23 |
23 |
| 24 hr Maximum |
23 |
26 |
45 |
| Winds |
| Current Winds |
9 SSW |
3 S |
- |
| 24 hr Average |
18 WSW |
10 WSW |
- |
| Maximum Gust |
51 WNW |
35 W |
- |
| Snow - Storm # 18 |
| New Snow |
4" |
3" |
0" |
| Storm Total |
10" |
10" |
2" |
| Total Depth |
56" |
49" |
24" |
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