In partnership with: Utah Division of State
Parks and Recreation, The Friends of the Utah Avalanche Center, Utah Department
of Emergency Services and Homeland Security and
The
Friends of the Utah Avalanche Center Home page is: http://www.utahavalanchecenter.com
Monday, June 2, 2005 Noon
This is
Avalanche
Information:
Spring, as you know, is the time of flip-flopping—when the weather can’t make
up its mind whether it’s winter or summer.
We usually get a cold, dry snow storm followed by hot summer-like
temperatures and strong sun. During the
storms, you need to operate in winter, dry-avalanche mode where you have to
carefully check the new snow to see how well it’s bonding to the underlying
snow and watch for the ever-present wind slabs, especially up along the wind
exposed ridges. As always, you should jump
on small test slopes and do slope cuts to test the snow. Always be suspicious of steep slopes with
recent deposits of wind drifted snow.
Click HERE
for a cornice-kicking lesson.
Then, after the storm, temperatures often warm dramatically and the
super-strong spring sun quickly turns the cold, dry new snow into damp or wet
snow. The mantra of avalanche
forecasting is that snow does not like rapid changes, and cold, dry snow
quickly turning into wet, soggy snow is one of the most rapid changes
possible. The snow gets cranky and shows
its emotions by producing roller balls and wet point-release sluffs on steep
slopes, especially under rocks that heat up in the sun. Then, if the percolating melt water
encounters buried weak-layers or ice crusts in the snowpack, it can create much
more dangerous wet slab avalanches because the percolating water dissolves the
bonds between the grains of buried weak layers. Click HERE
for some photos. If that’s not enough
trouble, melt water can also pool up above the ground, which makes what we call
“glide”
avalanches, in which the entire snow cover moves slowly downhill like a
glacier until it finally decides to let loose in a large, catastrophic
avalanche. Although wet slab avalanches
tend to occur in the heat of the afternoon, glide avalanches can come down any
time of day, even in the coldest time of the morning. So in spring you should always avoid crossing
underneath glide cracks, which you can find in abundance in places like Stairs
Gulch and Broad’s Fork.
Luckily, this kind of monkey business doesn’t last forever. After a week or two of percolating melt
water, the snowpack layers disappear, the snow becomes much denser and the
whole mess turns into a very strong, consolidated, summer-like snowpack. As of this writing, the snowpack at most
aspects and elevations seems to have settled and stabilized into a summer-like
snowpack and I think that wet slab avalanches will be quite rare for the rest
of the summer. However, we could still
get some wet sluffs after snow storms and wet sluffs during very hot weather,
especially in the heat of the afternoon.
The take-home point here is to get out early and get home early. The coldest
part of the day is usually just before dawn and wet avalanches usually occur in
the afternoon. If you’re sinking into
wet snow past your ankles, you should get off the slope.
Most people love spring because of the corn snow, or what avalanche folks call
melt-freeze snow. The game with corn
snow is to get onto it just after the sun has soften up the hopefully frozen
and supportable crust, and to get off of the snow before it gets so warm that
you punch through the crust into the wet snow below. Start with east facing slopes in the morning,
and change to south facing slopes by mid morning and onto west facing slopes by
late morning and go home by noon. You can usually tell if the snow surface has
refrozen overnight by checking the automated
weather stations on the Internet.
Luckily, Alta will leave Collins study plot operating through the summer. Remember that snow can loose a tremendous
amount of heat just by radiating its heat into a clear sky, so even with air temperatures
in the mid to upper 30’s, the snow surface can freeze as long as the sky is
clear. On cloudy nights, you will
definitely need below freezing temperatures.
For weather forecasts, visit the excellent National Weather Service web site
at: http://www.wrh.noaa.gov/slc/.
For weather computer models, I like
Finally, remember that all the ski resorts are closed for the season and they
are not doing any avalanche control. So
you need to treat them like the backcountry and follow the usual safe-travel
ritual, like one-at-a-time, don’t travel above other people and get out of the
way at the bottom.
We would still like to know about any avalanche activity especially if
people are involved so please continue to leave us messages at 524-5304 or
1-800-662-4140, or e-mail us at [email protected]. Fax is 524-6301.
You can read our annual report on our web site and it should be finished
by about mid June.
Thanks for your support this
season and we will talk to you again in November.