Avalanche Advisory Archive Pre-2016

Date Issued:2011-02-07
Danger:1
Trend:3
Probability:1
Size:2
Problem:0
Discussion:

The National Weather Service Forecasts-

TODAY...MOSTLY SUNNY. HIGHS AROUND 28. SOUTHEAST WIND 10 MPH.

TONIGHT...MOSTLY CLEAR. LOWS 17 TO 25. SOUTHEAST WIND TO 15 MPH.

TUESDAY...INCREASING CLOUDS. HIGHS AROUND 31. SOUTHEAST WIND
10 MPH.

TUESDAY NIGHT...CLOUDY. CHANCE OF SNOW. LOWS AROUND 29.
SOUTHEAST WIND 10 MPH.

We received quite a bit of rain all the way to mountin top level last week.

Temperatures have been slowly cooling over the last 4 days now.

The lower snowpack is fairly solid and locked in place.

Friday night we received about 4\" of new snow and have seen some light to moderate transport winds since then.

Small isolated slabs may have formed near summit and ridgeline.

With exception of those small surface slabs we are not worried about avalanches of any size at this time.

Tip:

Slope Shape:

Whether a slope is concave, convex, or planar makes some difference in avalanche danger, usually not a significant difference. Avalanches happen on any steep slope without thick anchors despite the shape of the slope. Slope shape makes more difference on smaller slopes than on larger ones.

Convex slopes statistically produce more avalanches and more avalanche accidents than other kinds of slopes, partly because they are inherently less stable and partly because they present more safe travel problems than other slopes.

? Convex slopes have less compressive support at the bottom than other slopes, which makes a difference for small avalanche paths, some difference on medium sized avalanche paths but has little effect of large avalanche paths.

? Convex slopes tend to wind load more than other slopes. (Wind slows down as it rounds the convexity which causes it to drop its load of snow.)

? Convex slopes are tricky to descend because each step or turn you take adds another degree of steepness until suddenly you find yourself on terrain that's too steep. But you can also use this to your advantage. With a soft slab, if you descend slowly, especially jumping on the snow or slope-cutting while you descend, the avalanches tend to break at your feet instead of above you more so than on planer or concave slopes. (Remember that hard slabs tend to break above you no matter what.)

? Convex slopes are difficult to assess because the conditions you find on the upper flat part of the slope often are much different than on the steepest part of the slope where you will most likely trigger an avalanche. For instance, there are a number of stories in which someone digs a snow profile on the upper section, pronounces the slope safe, then triggers an avalanche on the steeper part below.

? When descending a convex slopes they are difficult to exit if you start to find dangerous conditions. You have to climb back up. All too often people would rather risk their life by descending than to climb back up.

? Probably the most dangerous shapes are double convexities--convex vertically and horizontally--like dropping off the edge of a basketball. These slopes tend to wind-load both from the top and from the side, they have no compressive support and are very difficult to descend, ascend or cross safely. If you're lucky, the wind will erode one side of the slope and wind-load the other side allowing you to choose the safer eroded side.