Avalanche hazard has decreased now that we are over 48 hours out from the last storm. However, the potential for new wind loading and overloaded persistent weak layers will keep the hazard elevated.
Natural avalanches are possible and human triggered avalanches are likely, primarily above 11,000 on northeast and easterly aspects. Northwest, north and possibly southeast aspects should be considered suspect.
Travel in avalanche terrain near and above treeline will be least reactive on west, southwest, south and southeast slopes, as long as the slopes are not connected to northwest and easterly slopes. Hopefully the right combination of wind/clouds/temperatures will keep the snow in good shape on these sunny slopes. But remember, improving stability does not mean that no avalanche hazards exist.
Snowslide Canyon Bowl avalanched (photo below). This likely occurred between February 5th, Tuesday night and February 6th, Wednesday morning. This is primarily an east aspect with some southeast and northeast. The crown was over 600m wide, and it ran over 1100m (0.7 miles). There is more crown not shown in the photo that wraps around Snowslide Canyon. The average crown height was 1m with a maximum of 1.75m. The avalanche failed on facets near the ground. The bed surface was old snow and crusts. Characteristic classification is HS N R4D4 O.The slope angle was between 35° and 42°.
There is a report that Dunham Canyon may have also slid but this has not been confirmed.
Near and Above Treeline:Watch for older (February 6th) windslabs on easterly aspects and new slab development on northerly, northeasterly and easterly aspects. Winds are forecasted to blow south, southwest and west over the weekend.
Watch for reactive persistent weak layers. These may be buried under 2 to 5 feet of slab on east, northeast, north, and northwest aspects. Southeast aspects may be suspect as well, especially on slopes connected to easterly aspects.
Prior to this week's precipitation, wind scoured zones reduced the snowpack down to bedrocks in some areas. Also, sun and wind conspired to create hard snow prior to recent precipitation. Crampons may be helpful where new snow has been wind-scoured down to hard icy snow.
Below Treeline:Persistent slab instabilities exist in our snowpack. A reactive, faceted weak layer exists about 30 to 50cm from the ground, primarily on east, northeast, north and northwest slopes. It is not everywhere but recent avalanche activity indicated that it's still an issue. Carefully assess run out zones and terrain traps.
You will find great snow and low avalanche hazard if you stay off and do not get under slopes that are greater than 30°.
Watch for older (February 6th) and newer windslabs on north , northeast and easterly aspects. Winds are forecasted to blow south, southwest and west over the weekend, with a chance for snow on Sunday/Monday.
Post weekend winds may create slabs on other aspects. As always watch for cross loading in gullies. Slopes just below ridges and on the flanks of shoulders should be considered suspect.
Keep an eye on the ASBTP weather station. Readings between 15 and 35 mph indicate the potential for snow transport and formation of wind slabs. Look for various links under the weather menu above. Note that this station may get rimed during storms and report erroneously.
Weak faceted snow-layers under old and new wind/storm slabs exist at elevations above 10,000'. Column test in Beard Canyon on January 11th and near Alison Clay Bowl on February 4th indicating persistent slab problems. The Snowslide Canyon avalanche was triggered by wind loaded snow falilng on a persistent slab.
This problem has been found below, near and above treeline on northwest, north, northeast and east aspects. Our most reactive stability-test failures have occurred near and below treeline. The Snowslide Canyon avalanche crownline was above treeline.
This problem is not widespread and predicting its location has been problematic.
FREE Introduction to Avalanches seminar this Tuesday, February 12, at the SMR (Snow Mountain River) store in Flagstaff on South Milton. See our courses page to register for a class and get avy savvy.
Backcountry permits are required for travel in the Kachina Peaks Wilderness and available at local USFS locations, as well as, at the Agassiz Lodge on Saturday and Sunday 8:30 -11:30.
For information on uphill travel within the Arizona Snowbowl ski area, please refer to www.flagstaffuphill.com and https://www.snowbowl.ski/the-mountain/uphill-access/ for details. Access to the Kachina Peaks Wilderness is available from the lower lots at Snowbowl via the Humphreys Trail and Kachina Trail.
Weather updated February 8th.
The past week has been the wettest so far this winter. Arizona snowbowl (10,800') reported 42" of new snow since Feb. 2nd. Twenty inches fell between Feb. 5th and 6th. The Snowslide SNOTEL (9,730') reported 22" since Feb. 2nd and 9" since the 5th. SNOTEL reported 4.8" of new snow water equivalent (SWE) between Feb. 2nd and 6th.
In the aftermath of this storm cycle, cold windy conditions have prevailed. Determining accurate ridge-top wind velocities and direction has been impossible since the ASBTP station's anemometer was incapacitated with rime ice. Lower elevation stations, such as the Flagstaff Pulliam Airport (elev. 6994') reported wind speeds between 15-30 mph, gusting to 30-40 mph, throughout the day on Wednesday February 6th.
Cool blustery days will continue into the weekend with wind chill temperatures as low as -17 F on Friday and a chance of snow showers on Saturday from a passing shortwave trough. Ridge-top wind speeds will continue in the teens and higher, gusting to 30-40 mph out of the southwest throughout the weekend. More unsettled weather and a chance of light precipitation is predicted to develop early in the workweek. A more promising chance for significant new snow will come later in the week. Models disagree on impact and timing, but this appear to be a wet storm with a snowline at or above 8000 feet, probably arriving on Thursday, Feb. 14th.
On Friday morning, Feb. 8th, the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 50" (127 cm) at 9,730'. Arizona Snowbowl reported a settled base of 70" (178 cm) at 10,800'. So far this winter, 170" (432 cm) of snow have fallen at the mid-mountain study site. Since February 1st, SNOTEL temperatures have ranged between 5°F on February 7th, and 35° F on Feb. 2nd. For the same period, ASBTP (11,555') reported temperatures between -6°F on Feb, 7th, and 31°F on Feb. 1st and 2nd.