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Logan
Hello, this is Toby Weed of the
Current Conditions:
Backcountry snow conditions are
suffering from a few days of unseasonably warm temperatures in the mountains.
Upper layers of the snowpack are
saturated on most slopes and at all elevations. The snow on shallow lower elevation
slopes is isothermal, soaked through and through, and lacking any semblance of
structure is also very weak. Lower
elevation trails and roads melted out, and mud at the trailheads and the first
couple miles of your approach may fowl up your day. We found somewhat dry and fun soft snow
on the north-facing bed surface of a large natural avalanche at ~9400’ which
occurred during the storm two weeks ago, but even the darkest shadiest north
facing slopes where starting to get pretty sloppy by afternoon. Wednesday will
be mostly cloudy and warm in the morning, with clouds decreasing and
temperatures dropping a bit in the afternoon.
Avalanche
Conditions:
I’m
uncomfortable with these searing temperatures and the poor snow structure on
many slopes. Wet loose and slab
avalanches are the most obvious concern, but large dry slab avalanches are also
possible as the heat increases the creep rate of slabs overlaying old weak snow.
We have reports of a few
significant human triggered slab avalanches from Tuesday in the
Despite
a gradual cooling trend, wet avalanches will still be a problem on Wednesday.
I’ll feel better about things after
nighttime temperatures drop well below freezing for several hours. Warm temperatures are quickly melting
lower and mid-elevation snow and turning most slopes in the region very slushy.
The warmth is deforming cornices
and some have been failing, putting a good wallop on any slopes below. Wet
avalanches are possible on steep slopes at all elevations with saturated surface
snow. In some areas, a wet
avalanche overrunning a steep slope with persistent buried weak layers could
cause a deeper, potentially deadly hard slab release.
There are some areas where you still
might be able to trigger deep and dangerous hard slab avalanches, and the heat
in the past two days may have exacerbated the problem. I’d be most concerned in areas with a
shallow overall snowpack and therefore very weak early season snow. Rocky, wind-swept or exposed terrain at
upper elevations is suspect, especially on slopes exposed to prolonged
sunshine. On many upper elevation
slopes February’s slab is so thick that it would be difficult for a person to
trigger an avalanche unless from a shallow part of the slab. But, with the hot temperatures the slab
is creeping faster than underlying layers, and significant natural avalanches
may result. Also, the once hard
slab may have been softened by the heat and a slab which may have easily
supported your weight last week may now be sensitive to your presence on a
slope. In these conditions it’s
wise to keep in mind that the weight of a smaller avalanche overrunning some
slopes might be enough to trigger a deeper and much more dangerous hard slab
avalanche running on deeply buried persistent weak layers.
Bottom Line:
There is a CONSIDERABLE danger and wet avalanches are
probable on many steep saturated slopes at all elevations in the
backcountry. Persistent slab
avalanches are possible on some steep upper elevation slopes, and the problem
may be worsened by the recent heat-wave.
Dangerous hard slab avalanches are most likely in areas with shallow
overall snowpack, facing west through southeast, and above around 8000’ in
elevation. Avoid and stay out from
under slopes steeper than about 35 degrees, especially those with saturated
surface snow.
Mountain Weather:
A strong westerly flow aloft will be
over the region through Wednesday.
A weak cold front will move overhead early on Wednesday, bringing a
slight chance of a little snowfall and cooling temperatures. A high pressure will build in again for
the weekend, bringing more unseasonably warm days.
General Information:
Check out photos of last week's
avalanches in the Logan Area on our images
page.
Go to the Avalanche
Encyclopedia if you have any questions about terms I use in the
advisory. I also recommend the recently-released Media Page, which
shows the forecast danger for our coverage areas across the state.
Please e-mail me at
[email protected] or leave me a message at 755-3638 if you see or trigger
avalanches in the backcountry. The information you provide may save
lives...
This advisory will expire on
Wednesday evening. I will update it
again on Thursday evening.
The information in this advisory is
from the U.S. Forest Service, which is solely responsible for its content.
This advisory describes general avalanche conditions and local variations always
occur.
