Avalanche Advisory Feb 4, 2018

Bottom Line

The Avalanche Hazard is Moderate today. Lower elevation slopes are saturated and with a rain line near 7000 feet today, expect an increase in loose/wet avalanches. Wind slabs are the primary concern on upper elevation, exposed slopes that have been affected by SW, W and NW winds. Avoid traveling on steeper slopes with stiff or hollow feeling snow, watch for obvious texture changes and wind deposited snow. Cornices are starting to grow and will become less stable as temperatures warm.

Avalanche Problem #1: Wind Slab

Wind slabs have formed over the last week on several aspects. Winds have been consistent enough to create slabs of varying thickness on exposed upper elevation terrain. Some of these slabs may be resting on crusts or weaker layers of snow below them. Temperatures in the mid 30’s and rain to near 7000 feet today will make these slabs more touchy and more dense today and until we see a cooling of the snowpack. Pay attention to changing snow conditions as you approach exposed, wind affected terrain today whether you are traveling uphill or downhill. Watch for obvious signs of textured, pillowed or drifted snow as well as hollow sounding or feeling snow. Cornices are also starting to grow large and with increasing temperatures and the addition of heavy snow or rain, they will likely become more unstable as well. Avoid traveling on or under areas of large overhanging cornices.

Avalanche Problem #2: Loose Wet

Temperatures will continue to warm well into the 30’s as we receive more moisture through the day today. Below 6000 feet expect mostly rain with a mix of wet snow and rain in the upper elevations. Warm temps combined with rain will increase the potential for wet/loose avalanche activity on steep lower elevation slopes especially near rocks, road cuts and on slopes over 35 degrees today. Roller balls and pinwheels are great indicators of rising wet/loose avalanche activity.

Recent Observations

Winds were gusting out of the NW and W yesterday throughout the advisory area. Granite Mt. weather station saw gusts over 25mph yesterday and it sounds like the West Mountains in the Southern portion of the advisory area have seen W winds for several days as well.

Yesterday PAC forecasters toured in the Victor Trail area near Trail Lake and found a similar snowpack structure to what we found near Boulder Mt. on Thursday. The upper snowpack has several crusts that are starting to degrade. The older Thanksgiving crust is still present but the faceted layer has been diminished over time and is not reactive. The dirty layer between 40 and 60cm down is showing some consistent fracture results in our pit tests but lacks the ability to propagate. The exception right now is the thin rain/humidity crust near the surface, earlier in the week it showed the ability to collapse suddenly and propagate through our test pits.

Monumental Summit

Boulder ESE

Above Trail Lake


[?] to yesterday, with showers continuing across the central Idaho
mountains and well above normal temperatures across the region.
Record temperatures are again possible across southern areas where
more breaks in the cloud cover are expected. Precipitation chances
increase late this afternoon into tonight ahead of an upper short
wave trough entering the Pac NW. As with recent disturbances the
southern edge of precipitation will skirt northern Malhuer county
and the Snake Plain with a slight chance of showers through Monday
morning. Snow levels remain at or above 7k feet across the region
into Monday morning which will limit accumulations to higher
peaks. All areas trend drier during the day Monday as the wave
quickly exits the region. Will also see slight cooling in its
wake, which means well above normal temperatures, but not quite
reaching record territory. Have updated the PNS product for sites
forecast to approach records for today.

.LONG TERM…Monday night through Saturday…Northwest flow aloft
continues through much of the extended forecast. Moisture pressing
up and over the ridge axis stationed offshore will provide chances
of showers for the central Idaho mountains through the entire
extended period. The GFS has now come in alignment with the ECMWF
for Friday keeping the moist northwesterly flow and slight chance
of showers for the West Central Mountains. After Friday, models
diverge and confidence lowers. Temperatures remain above normal
throughout the period.


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.