Currently, a Winter Weather Advisory has been issued for most of the higher terrain of Northern Arizona, lasting through 5 pm today, December 28th. Snow accumulation is 4" for Snowbowl at 10,800' and 5" for the Snowslide SNOTEL at 9,730'. More snow is possible today and tonight. Light winds have resulted in little wind transport of the new snow.
High temperatures and strong winds last week created surface crust and wind slabs near ridgetops, at and above treeline on east, west and wind loaded aspects from 70 + mph north winds. The snowpack is thin, @ 60-80 cm in sheltered locations at treeline (@ 11,500'), and thus a temperature gradient exists within the snowpack forming depth hoar and near surface facets, which weaken the structure of the overall snowpack.
Observations from 12-27 indicate poor structure, moderate strength and low reactivity (see attached snow profile). However, near surface facets under these crusts and wind slab may prove to be a dangerous persistent weak layer with significant snowfall. Human triggered avalanches are possible, and natural avalanches are unlikely.
Early season conditions continue. The new snow has marginally improved touring, however coverage will remain spotty with hidden obstacles, especially on sun affected slopes. Over the weekend, ridgeline windchill values will dip to near -15° F.
No natural or skier triggered slab avalanches have been reported so far this winter.
Near and Above Treeline:Backcountry powder skiing has been in low supply for a while. Watch out for the scarcity heuristic trap, as it may lead you into thin powder snow full of hidden sharks. Coverage is still quite thin overall.
Steep isolated slopes near treeline have localized wind slabs from strong north wind last week. Current ASBTP winds indicate that new wind slabs may be a low probability. The new precipitation is very light and will be easily transported once wind speeds increase.
No significant wind drifts were observed near 10,800' this morning at 8 AM.
Below Treeline:Touring conditions have marginally improved with the current storm. At lower elevations the coverage is spotty with ample hidden rocks and logs. Sun affected slopes are very thin. On Christmas we found crusts overlaying sugary, faceted snow on many aspects below 10,000'.
With the new snow, decent cross country touring can be found near 9,000' on shady terrain. The snowpack is still thin, watch for hidden obstacles! The overall snowpack depth averages 30" above 10,500', and diminishes rapidly at lower elevations, especially south aspects.
Wind speeds at ASBTP have been light and our confidence in finding any significant new wind slabs is low. No significant wind drifts were observed near 10,800' this morning at 8 AM.
Localized wind slabs from previous wind loading exist on cross loaded slopes and ridgelines at and above treeline. Strength and cohesion of these slabs are variable and may fracture in isolated locations. Hollow sounding snow and whumpfing are indicators of hard slabs and should be avoided. Evaluate each slope before skiing.
Keep an eye on the ASBTP weather station. Speeds between 17 and 25 mph are ideal for transporting snow and creating wind slabs.
With the very cold temperatures, check to see if the new snow has bonded to the old snow. With the light amounts of snow this problem may be nonexistent, but watch for it on steep slopes near and above treeline.
The bulls eye slope angle for avalanche activity is 38 degrees. Moderating slope angles to 30 degrees and less drastically reduces the likelihood of triggering an avalanche.
See our courses page for upcoming free courses, including a FREE Introduction to Avalanches Seminar at Aspen Sports on January 3.
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 a.m.
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.
Currently from 5 pm Thursday through 5 pm Friday (December 28th) much of the higher terrain is under a Winter Weather Advisory. So far accumulations have been on low, with AZ Snowbowl reporting 4" as of 9 AM today, December 28th.
By Saturday and Sunday we will feel the coldest temperatures so far this season,
with single digit lows across much of the plateau, and high temperatures likely below freezing.
Flagstaff highs will likely remain near freezing as another weather system looks to impact the area, starting New Years Eve.
On December 20th, Flagstaff hit 62° F. The warmest December temperature in 100 years. The Christmas storm produced only one inch of snow at 10,800'. SnoTel reported less than an inch.
On Friday morning, December 28th, the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 17 inches (43 cm) at 9,730 feet, and Arizona Snowbowl reported a settled base of 33 inches (84 cm) at 10,800 feet. So far this winter, 48 inches (122 cm) of snow have fallen at the mid-mountain study site.
Since December 21st, SNOTEL temperatures have ranged between 6°F on December 27th, and 48°F on December 21st. For the same period, the AZ Snowbowl Top Patrol Station (ASBTP 11,555 feet) temperatures ranged between -1°F on December 28th, and 33°F on December 24th.