Date Issued: | 2013-04-07 |
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Danger: | 1 |
Trend: | 3 |
Probability: | 1 |
Size: | 2 |
Problem: | 0 |
Discussion: | From the National Weather Service: .TONIGHT...PARTLY CLOUDY. PATCHY FOG LATE. LOWS AROUND 32. EAST .MONDAY...BECOMING MOSTLY CLOUDY. CHANCE OF RAIN IN THE AFTERNOON. The snow line rose past our urban slide path start zones yesterday afternoon, though with temperatures remaining a few degrees above freezing overnight. Slowly rising temperatures and minimal precipitation have been the hallmark of this weather system, allowing time for adjustment in the snow pack as the weather changes over to wet over the next 48 hours. The primary concern today is rising temperatures, though in general the weather today will be very similar to yesterday. Natural avalanches are very unlikely over the next 24 hour period, putting our hazard at LOW with a 24 hour trend of SAME. The start zones have had time settle and adjust to the warmer weather, which has been moderate over the last few days. Be cautious if heading out the Flume or Perseverance. |
Tip: | All about Wet Avalanches Most avalanche professionals make a hard separation between wet snow avalanches and dry snow avalanches, because wet and dry avalanches are so different. You forecast for wet and dry avalanches very differently, much of the mechanics are different, they move differently, and it's only natural for us to think of them as two separate beasts altogether. But really, there?s a continuum between wet and dry avalanches. For instance, there are damp avalanches, and often, large, dry avalanches start out dry and end up wet by the time they get to the bottom because either the energy of the descent heats the snow up or they travel into a region of warmer snow. Like dry snow avalanches, wet avalanches can occur as both sluffs and slabs. Wet avalanches usually occur when warm air temperatures, sun or rain cause water to percolate through the snowpack and decrease the strength of the snow, or in some cases, change the mechanical properties of the snow. Once initiated, wet snow tends to travel much more slowly than dry snow avalanches--like a thousand concrete trucks dumping their load at once instead of the hovercraft-like movement of a dry avalanche. A typical wet avalanche travels around 15 to 30 km/hr (10 or 20 mph) while a typical dry snow avalanche travels 100 to130 km/hr (60 or 80 mph)--big difference. Wet slides are also harder for a person to trigger than a dry slide. Because of these two facts, wet avalanches don?t account for nearly as many avalanche fatalities as dry snow avalanches. But they?re certainly not insignificant. They still account for a sizeable percentage of avalanche fatalities in maritime climates, especially to climbers. Wet slides can also do quite a bit of damage to property or to forests and often cause significant hazards on highways. (from http://www.fsavalanche.org/encyclopedia/avalanche.htm) |
Forecaster: | Peter Flynn |