4/27/2011
Reed Hollinshead
ITD Communication
208-334-8881
reed.hollinshead@itd.idaho.gov
Fueled by warming weather, wet spring and melting, avalanche season extends into May on Idaho 21
BOISE COUNTY - Warmer weather and the first signs of spring generally are cause for celebration - birds chirp, flowers bloom, fresh breezes blow. For ITD's avalanche forecasters on Idaho 21, however, it often means things are about to get touchy.
Often, the onset of warm, spring weather brings unwelcome consequences as the snowpack starts to melt and combines with spring rains to create instability in the notorious "Avalanche Alley" section between the Grandjean Junction turnoff and Banner Summit. Avalanche Alley is home to about 60 avalanche chutes and 90 percent of the avalanches in the state that affect highways.
After setting records the last few years for fewest closure days, including just nine days of closure last year, the route has seen 380 inches of snowfall since November and 18 days of closure. The winter season in the Avalanche Alley region unofficially runs from Dec. 1 through April 30 each year. Late November snowstorms are not uncommon, however, and Mother Nature does not hold fast to the spring timeframe either.
Colder temperatures can actually help stabilize the existing snowpack.
Bill Nicholson, ITD's head avalanche forecaster, noted that while the amount of remaining snow is significant, the more important indicator in warm-weather conditions is the temperature of the snow at different depths.
"As spring weather warms, the snow becomes more slushy during the hot part of the day and usually refreezes at night," he explained.
"The temperatures help us get a picture of how deeply the warmth is penetrating the snowpack and can foreshadow avalanches."
Questions? Visit us online at itd.idaho.gov, follow ITD on Twitter (IdahoITD) or Facebook and check travel conditions at 511.idaho.gov or dial 5-1-1. Please slow down in highway construction zones and pay attention. Safety for drivers and workers is our highest priority.