In
partnership with: The Friends of the Utah Avalanche Center, Utah Department of
Public Safety Division of Comprehensive Emergency Management,
For photos of avalanches and
avalanche activity, visit: http://www.avalanche.org/%7Euac/photos_03-04.htm (Updated
3/25)
Photos sent in by observers
throughout the season visit: http://www.avalanche.org/~uac/obphotos/observer.html (Updated
4/2)
For a list of backcountry avalanche
activity, visit: http://www.avalanche.org/%7Euac/Avalanche_List.htm (Updated
3/31)
Avalanche INFORMATION
Monday, May 03, 2004 2:00 pm
Hello, this is the
This does not mean the end of
avalanches for the year. It just means
that the money has run out and all of our staff is off doing other things for
the summer. So you’re on your own. Here’s a few rules of thumb on what spring
usually brings in the avalanche department.
First, as you may imagine, we
have to worry about wet avalanches. The name
of the game in spring is to get out early and get off the snow early. In other words, if you’re sinking in past your
ankles then it’s time to head to a more shady slope or head home. The worst wet slides tend to happen on
snowpack that are going through the transition from a cold, dry snowpack to a
wet one. As melt water percolates down
through the layers, they can saturate fine grained layers of snow like a sponge
or they can pool up above ice crusts. Then
the snow becomes saturated it can very quickly turn into margaritaville and
slurp on down the mountain like a thousand concrete trucks dumping their load
at once. But the good news is that after
melt water has percolated through a snowpack for just a few days, it dissolves
all the layers and all the snow becomes larger grained, very porous and very
stable. As spring progresses, usually
the south facing slopes become stable first, then in mid spring, the east and
west facing slopes. Then in late spring, the upper elevations north facing
slopes are the last ones to go through a wet slide cycle and then become very
stable. You should especially watch out for one or
more nights where the snowpack does not refreeze. So how do you judge that from town? First you get on the Internet and check out
the automated weather stations. Snowbird has the only mountain stations still
working in spring. Also, be sure to check
the date and time because sometimes the weather stations are not working or
sometimes the computer servers are down for some reason.
Snowbird
Gad Valley graph (9,800’)
Snowbird Gad
Valley table (9,800’)
Snowbird
Hidden Peak graph (11,000’)
Snowbird
Hidden Peak table (11,000’)
Snow surface temperature
depends on both air temperature and on cloud cover. Snow is a very efficient radiator of heat and
with a clear sky, the snow surface can radiate a tremendous about of heat away.
Even with an air temperature in the
upper 30’s the snow surface can still refreeze with a clear sky and low
humidity. With cloud cover, though, the
air temperature has to be below freezing. Also,
in spring we have to watch out for steep, rock slabs because it’s common for
them to produce what we call “glide” avalanches, meaning that the entire
snowpack slides slowly down the rock slabs kind of like a glacier until it
releases catastrophically at random times. These tend to occur after several days of very
warm temperatures but they can occur randomly too and even with a frozen snow
surface. So watch out for places like
Stairs Gulch and Broads Fork, which are notorious areas for glide avalanches.
Finally, you will need to
watch out for the usual round of new snow avalanches and wind slabs every time
we get a spring snowstorm. As always,
avoid any steep slope with recent deposits of wind drifted snow and you should
jump on several small test slopes as you travel to test how well the new snow
is bonded to the underlying snow. And
when the new snow gets wet for the first time, it almost always produces damp
to wet sluffs on steep slopes.
Well, that’s the basics.
I should be done with our
annual report by about mid May and I will post it on our web site if you’re
interested. Also, if you want a hard
copy, just leave a message at 524-5304, 1 800-662-4140, drop us an email at [email protected], or a fax to
524-6301.
Thanks for a great
season and we’ll be talking with you again next fall.
The
information in this advisory is from the US Forest Service, which is solely
responsible for its content. This
advisory describes general avalanche conditions and local variations always
occur.
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