After the "Snowcopia" of "White Friday", snowpack coverage is getting quite good, but thin spots can still be found at lower elevations and on scoured slopes at higher elevations. The two November storms contained enough moisture to rank November 2019 as the 5th wettest on record for Flagstaff. Last week's (Thanksgiving/White Friday!) storm deposited up to 47" of snow at 10,800 ft, and it's no surprise that natural avalanches occurred.
There was a natural avalanche near 11,700 ft on a northeasterly slope in Humphrey's Cirque near treeline. Another natural avalanche on more northerly through northeasterly aspects occurred near the top of Core Ridge. Both avalanches appeared to have initialed at the old and new snow interface in a graupel layer, likely releasing sometime on November 29th or early on November 30th.
Arizona Snowbowl Ski Patrol observed natural avalanche debris from the evening of the 29th and triggered an avalanche with explosives on Saturday, November 30th, on a north aspect at 12,000'. Strong south and southwest winds during the Thanksgiving storm loaded north and east aspects.
The storm snow has settled rapidly over the last few days, and evidence of increasing stability has been noted. However the graupel layer (discussed above) did indicate a propensity to propagate failures during December 1 stability tests.
These tests were performed near the natural avalanche of Humphrey's Cirque (discussed above). So far the graupel layer has only been observed on ~northerly slopes in the Humphrey's Cirque and upper North Core Ridge area. No avalanche activity has been observed on west - south - east aspects.
More rain and snow is expected Wednesday through Thursday morning with 9 to 15 inches and south-southwest-west winds forecasted near treeline. Rain is forecasted below 9,000 ft.
Near and Above Treeline:Current forecast calls for 9-15" of new snow near treeline on Wednesday/Thursday, along with 20+ mph south-southwest-west winds. Watch for new wind slabs on north, northeasterly and easterly slopes. Gullies and chutes of westerly, easterly (and possibly southerly) aspects may get cross loaded.
Coverage is approximately 1.5 meters, excluding wind scoured areas and areas that avalanched during the last storm. View recent snow study pits. Measurements of 2 meters of snow were reported from ~12,000 ft in Humphrey's Cirque on December 2nd.
Below Treeline:Rain is forecast below 9,000 ft. Rain on snow could lead to avalanches at lower elevations. Watch out for rain melting the snow into wet unconsolidated slush. Avoid steep slopes (especially in canyons) where rain is saturating the snowpack. Rooftops loaded with November snow may unexpectedly shed during a rain event. Roof avalanches can pack a surprising punch.
Coverage for ski touring is fantastic for early December, but early season hazards such as downed trees, stumps, and boulders may still remain hidden near the surface at lower elevations. Coverage above 9,000 ft is generally 1+ meter of snow. Good touring has been found all the way down to 7,500 ft on slopes with few rocks and plant debris.
Current forecast calls for 9-15" of new snow near treeline on Wednesday/Thursday, along with 20+ mph south-southwest-west winds. Watch for new wind slabs on north, northeasterly and easterly slopes. Gullies and chutes of westerly, easterly (and possibly southerly) aspects may get cross loaded.
This problem should be confined to near and above treeline terrain. Wind Slabs are most reactive during formation, and the first day or two after.
Rain is forecast below 9,000 ft. Rain on snow could lead to avalanches at lower elevations. Watch out for rain melting the snow into wet unconsolidated slush. Avoid steep slopes (especially in canyons) where rain saturates the snowpack.
Should we get significant lower elevation rain, then rooftops fat from late November snow may unexpectedly shed. Rooftops that face north, northeast and east are the most suspect, as that is where most of the snow has loaded.
Wet avalanche probability will decrease dramatically as the temperature drops below freezing Wednesday night and Thursday morning.
Roof avalanches can pack a surprising punch. Rooftop avalanches are generally characterized as a wet slab problem.
As of December 2nd, 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 December 3, 2019
Last week's "White Friday Storm" was the second snowiest November day on record, and the snowiest November 29th day on record for Flagstaff. Our two November storms contained enough moisture to rank November 2019 as the 5th wettest on record for Flagstaff. Since then a slight warming trend has kept temperatures near and above average. Post storm, above freezing temperatures, high relative humidity, light winds and cloud cover have quickly settled the snowpack at high elevations.
A fast moving Pacific trough will cross Arizona on Wednesday and Thursday. The rain/snow line is forecast to start in the 7,500 to 8,500 ft range on Wednesday then drop into the 6,500 to 7,500 range by Thursday morning. Models are showing approximately 1.0 inch of water with this system.
Arizona Snowbowl Ski patrol reports a 45" base at 10,800 ft. Snowslide SNOTEL reports a 35" snow depth, down from a November 30th high of 52".
Since November 29, SNOTEL temperatures have ranged between 6°F on November 30th, and 44°F on December 2nd. ASBTP station (11,555') reported a low of 0°F on November 30th and a high of 41°F on December 2nd.