Our second significant storm of the season arrived this week. Rapid accumulation of new snow will increase the probability of dangerous avalanches. For 24 to 48 hours following the end of the storm, natural avalanches will be possible and human triggered ones are likely. Early season conditions prevail with a thin, unconsolidated snowpack.
With significant redistribution of the snow from last week's storm, backcountry snow coverage is highly variable. Hidden obstacles beneath poorly compacted snow may still remain. Strong southerly and southwesterly winds blew Monday through Wednesday, potentially creating wind slab problems on steep (>30°) slopes. Wind slabs will be found mainly on leeward aspects (N, NE). Newly formed wind slab may be hidden below snow from the Thanksgiving Day storm, which we are still in the midst of. High elevation storm totals are predicted to exceed 24 inches near treeline creating a significant load on the snowpack below.
The snow falls beckoning the romantic,
piling in sensuous pillows,
masking the chaos of life
Like all mysteries snow has intrigue, but
Allure as lure, resist the bait.
As one might imagine, two feet of new snow and brisk winds will create the potential for storm snow avalanches and wind slabs. Although surface hoar was observed last week in the aftermath of our opening storm, it seems unlikely that these fragile crystals will have survived wind events earlier in the week. If surface hoar remains buried deep below new storm snow, it will reside only in very wind protected zones below treeline.
Also, it seems unlikely that sufficient time has passed between the first and second major storms to allow other persistent weak layers (depth hoar or near surface facets) to develop, though some weak remnants of October snow may remain on shaded aspects.
Near and Above Treeline:A lot of high elevation snow was moved earlier in the week from windward to leeward slopes, or has been stripped altogether and returned to the atmosphere. New snow has filled in making it challenging to assess snowpack depth , coverage, and structure. The settled base as reported at Arizona Snowbowl is currently 45” (114 cm) at 10,800 feet.
Wind slabs, potentially hidden below new storm snow on steep (>30°) slopes may exist near and above treeline. These could create hazards to skier ad snowboarders and may not be detectable underfoot. At the moment, this is speculative, as observers have not had the opportunity to fully evaluate backcountry conditions. Make sure to evaluate slopes individually by digging a snow pit, evaluating bonding between new snow and old, and keeping an eye out for recently buried and reactive wind slab.
Below Treeline:Below treeline the snowpack is still relatively shallow, unconsolidated, and deceptive. Hazardous obstacles such as downed trees, stumps, and boulders may still remain hidden near the surface.
More than 27" of new snow in 24 hours with winds in the 15-40 mph range create red flag conditions for storm slab avalanches. For the near term, travel in avalanche terrain is not recommended. These fragile conditions are likely to heal relatively quickly as new snow bonds with the old. Skiing and boarding safety will be significantly enhanced by waiting 48 hours after the skies clear and winds subside before entering steep (>30°) snow loaded terrain .
Winds Monday - Wednesday may have created wind slab problems on steep slopes (>30°) near and above treeline. Wind slabs may have subsequently become buried beneath new storm snow, hiding this problem from view and the feel under your skis. The added snow load may also increase the potential size and consequence of what may have otherwise been a smaller avalanche. These conditions will be most prevalent on north, northeast and east facing slopes.
Loose snow avalanches are likely to occur on steep terrain (>35°). Caution should be taken when traveling on steep slopes, particularly above cliffs, exposed rocks, and confined gullies where being swept away would more likely result in traumatic injury rather than complete burial.
As of November 29, uphill travel at the Arizona Snowbowl is currently closed.
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.
Updated November 29, 2019
Two potent storms in less that a week, what a great way to set winter in motion. A cold front, early last week, brought 2 inches of snow to Snowbowl, and a lot of wind early in the week. Temperatures stayed mostly below freezing at high elevations throughout the week.
Thanksgiving day ushered a storm anticipated to last until Saturday morning. It will feature strong winds out of the south and southwest, and abundant snowfall at elevations above 6000 feet. This storm is very similar to our last big one, characterized by a deep digging low, a subtropical moisture tap and cold advection influenced by a strong mid latitude cold front.
Snowbowl reported 27” (53 cm) of new snow on Friday morning all falling within the previous 24 hours and an additional15” (38 cm) forecasted before the storm’s ends. Snowslide SNOTEL reported a total snow depth of 32” (81cm) early Friday morning, of which 20” was new. At least 2” of new Snow Water Equivalent (SWE) was added to the snowpack at the time of publication.
Looking on toward the weekend and beyond, expect snowfall to taper off on Friday evening or Saturday morning, leading to partly cloudy conditions for the weekend. The workweek will bring gradually warming and more settled weather.
Since November 23rd , SNOTEL temperatures have ranged between 9°F on November 26 and 36° F on November 24. ASBTP station (11,555') reported a low of -1°F on November 26 and a high of 46°F on November 24.