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| 3.27.2009 |
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This is Chris Lundy of the Sawtooth National Forest Avalanche Center with your Backcountry Avalanche Advisory and Weather Forecast for Friday, March 27, 2009 at 7:30 am.
Smiley Creek Lodge & Marley in the Mountains & the Friends of the Sawtooth Avalanche Center bring you this advisory.
Special Announcement:
The Avalanche Center is winding down it's winter operations and will issue the last daily avalanche advisory of the season this Sunday. We will continue to provide periodic general snowpack information through early April.
Bottom Line:
Today the avalanche danger is estimated to be MODERATE. Especially in our northern mountains where the recent storm produced 4-8 inches of new snow, yesterday’s northerly winds loaded the lee sides of ridges and cross-loaded mid-slope ribs, gullies and other terrain features. These wind slabs showed signs of sensitivity yesterday and may remain touchy today. With less new snow available for transport, wind slabs will not be as prevalent in the South and Central Valley.
Wet Snow Stability: A good re-freeze occurred overnight at all elevations, but pay attention to increasing wet slide danger on steep, sunny aspects as the day heats up. Be most heads up in our northern area, where recent snowfall may come unglued from underlying crusts.
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Danger by Aspect and Elevation:
Primary Avalanche Concern:
The fast-moving storm that blew through Wednesday night dropped 4-8 inches of low density new snow in our northern mountains, with rumors of up to a foot of further to the west. While not a serious stability problem in itself, north winds that continued through yesterday afternoon made short work of transporting the new snow onto leeward terrain features. In Baker Creek yesterday, we watched as snow blew over ridges and created classic pillowed wind slabs on the lee side of ridgelines and mid-slope ribs and gullies (see photo).
Watch for the tell-tale pillowed appearance in upper elevation terrain, and pay attention to the feel of denser snow underfoot. These wind slabs were sensitive yesterday, and it may remain possible to trigger one today. Once you identify wind drifted areas, avoidance will be the best approach.
The mountains in the South and Central Valley received only a few inches from Wednesday night’s storm, and with less snow to blow around, sensitive wind slabs will be less common.
Secondary Avalanche Concern:
With warmer temperature and sunshine, wet slides will be more of a concern today than during yesterday’s cooler weather. Problems will likely occur first in our northern mountains where newer snow is sitting atop old crusts. As this new snow warms up, it will likely come unglued on steep slopes that face the sun. I would expect some natural wet sluffs to occur today, especially on rocky slopes steeper than about 40 degrees.
The mountains closer to town received only an inch or two of recent snow, and the snow surface on sunny slopes remains in a predictable melt-freeze cycle. With a good freeze overnight, this crust will be hard and supportable this morning, becoming progressively weaker through the day. The snow surface in this region has already been put through the wringer with very warm temperatures and rain, so today’s moderately warm temperatures won’t come as much of a shock. Still, use caution as the day heats up and south-facing crusts become weak and punchy.
Current Conditions:
Baldy and Titus weather stations seem to be under-reporting the wind speeds yesterday, with stronger northerly winds observed in the field. However, the Soldier Mountain weather station recorded winds averaging 40 mph before tapering off around noon. Despite some sunshine, the north wind kept temperature on the cool side, and highs at upper elevations only reached the upper 20s to low 30s.
In our northern area, fresh powder conditions exist on sheltered slopes, while more exposed terrain will have some effect from yesterday’s wind. In the mountains closer to town, today should provide good corn conditions on sunny aspects. With a solid freeze overnight, and only moderate temperatures in the forecast, you shouldn’t have to be in too big of a hurry.
Mountain Weather Forecast:
Today’s weather forecast is rather unremarkable, with moderate temperatures, light winds, and a few clouds. A northwest flow remains in place, but warmer air is beginning to push into the area in advance of a minor storm system forecast to arrive tomorrow. Skies will start out partly cloudy today, with increasing clouds expected this evening. High temperatures in the mountains should reach the upper 20s to mid 30s, and in town it should hit the low 40s. Ridgeline winds are forecast to average 5-15 mph from the northwest.
Photos:
1. Wind loading in Apollo Creek
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| Reported Conditions |
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| Temperatures |
| Overnight Low |
5 |
14 |
13 |
| 6am Temperature |
8 |
14 |
13 |
| 24 hr Maximum |
28 |
36 |
36 |
| Winds |
| Note: Actual winds observed to be stronger than reported |
| Current Winds |
13 W |
3 W |
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| 24 hr Average |
8 W |
4 NW |
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| Maximum Gust |
21 NNE |
27 NNW |
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| Snow - Storm Interval # 25 |
| Total Depth |
71" |
58" |
21" |
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