Avalanche Advisory Feb 11, 2018

Bottom Line

The risk of triggering an avalanche is generally Low throughout the PAC advisory area today. Warm temperatures and a lack of significant snow accumulations have allowed the snowpack to strengthen over the last two weeks. High elevation ridgelines and other features may still harbor scattered windslabs that are sensitive enough to trigger especially where they are resting on firm snow or crusts below. Use normal caution while traveling and good group management. Remember, Low Hazard does not mean No Hazard.

Avalanche Problem #1: Wind Slab

Wind slabs have been our main problem for a good portion of the winter this year. We have not seen or had reports of natural or human caused avalanches for several weeks in the PAC advisory area. Warmer than normal day time temperatures and light precipitation over the last 2-3 weeks have allowed the snowpack, including the windslab problem to strengthen quite a bit. With cooler temperatures in store this week, this snowpack will continue to strengthen.

We have been seeing winds over the last few days gusting into the mid to upper 20 mph range but there is generally very little soft snow available for transport, so any new slabs that have formed are likely to be relatively thin.

Don’t let your guard down though if you are skiing or riding in high consequence terrain, plan for and anticipate the presence of thin windslabs especially on northerly and east facing aspects. Any windslabs that are lingering are likely resting on a firm old snow surface below and if triggered will want to run fast. Small, fast moving sluffing will also be a concern on very steep terrain. Remember, just because the hazard is Low doesn’t mean that it is 100% safe. Low hazard means that you may still find small avalanches in isolated areas or extreme terrain.

Advisory Discussion

The Friends of the Payette Avalanche Center is hosting a night of Bluegrass and gear raffles at the the McCall Golf Course on Friday, Februrary 23 at 7pm. Cost at the door is $10 which includes a raffle ticket and admission for music. The proceeds of this event will help support the Payette Avalanche Center and the future of its programs in the McCall area.

Recent Observations

We toured a lot of country Thursday and Friday, in the Granite, Goose and Fisher Creek areas on Thursday and near Green Mountain and Rapid Creek Friday. The quality of the snow varies quite a bit by elevation with a breakable crust being the highlight. Above 7400 feet the crust is less noticeable and there is 2-3 inches of new snow on the old firm snow below that made for good riding and sidehilling. Below 7400 feet it is a mixed bag of somewhat supportable to supportable crusts that make for go anywhere sled conditions…just don’t plan on sticking a sick sidehill on the way. The snowpack has done a great job consolidating after the last round of warm precip last weekend and lacks any notable instabilities in the upper 3-4 feet. We found a few buried crusts that failed in compression but lacked the ability to propagate across our test blocks. Wind transport was noticeable on the highest peaks Frirday afternoon but with only a few inches of fluff to move around, we did not see signs of significant loading or new wind slab formation. A major cool down occurred as a cold front blew in Friday afternoon which kept the snow pretty firm throughout the day except for in very low elevation areas. See the crust picture below, notice the snowmobile ski penetration is very shallow. This was on a south facing slope at 1:00 pm Friday afternoon. The next picture is of a northerly pit from Thursday with several crust layers visible that are slowly breaking down in an otherwise very stable snowpack.

Weather

Area Forecast Discussion
National Weather Service Boise ID
316 AM MST Sun Feb 11 2018

.SHORT TERM…Today through Monday…A northwesterly flow aloft
will turn briefly west, and then southwest as a trough drops
south from the Gulf of Alaska and into the Pacific Northwest.
Light snow showers will begin across southeast Oregon as early as
this evening, and spread across the region tonight and into early
Monday morning as the trough continues its journey to the south
and east. A reinforcing shortwave circling through the trough will
continue light snow showers across east-central Oregon and west-
central Idaho mountains overnight. Snow showers will remain
across the Nevada border and north through the Magic Valley Monday
as the trough digs farther south and east into Utah. Snow levels
will reach valley floors overnight. However, snowfall totals will
be generally light through the period. Highest snowfall amounts
(2 to 4 inches) will occur across the higher elevations along the
Idaho-Nevada border where a deformation zone may set up; of
course, any adjustment to this boundary location will
significantly alter the forecast in these locations. Dry
conditions return to all areas by Monday evening. Breezy northwest
winds are expected Monday as the trough axis exits to the
southeast, especially along the I-84 corridor, Baker City through
Mountain Home. Temperatures will remain near normal through the
period.

.LONG TERM…Monday night through Saturday…Cold and dry Tuesday
with clear skies and light surface winds and northeast flow aloft.
Min temps Tuesday have been lowered several degrees. Not as cold
Tuesday night. Next upper trough from the north will bring a
chance of snow showers Wednesday (rain below 3000 feet) with a cold
front midday, followed by windy cooler weather Wednesday afternoon.
High temps Wednesday may occur in the morning. Thursday looks dry
with temps similar to Wednesday, although models disagree with ECMWF
noticeably colder than GFS. For now will go with a blend.

.AVIATION…VFR. Increasing clouds from west to east. Snow showers
developing over the mountains after 20Z with terrain obscuration
developing after 12/00Z. Light surface winds. Winds aloft at 10
kft MSL westerly 20 kts.

Disclaimer

This avalanche advisory is provided through a partnership between the Payette National Forest and the Payette Avalanche Center. This advisory covers the West Central Mountains between Hard Butte on the north and Council Mountain on the south. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

source:
——————————–

Advertisements