The storm that was previously forecasted as lacking significant moisture has found its juice. Apparently tapping into sub-tropical humid flow, this storm has developed a massive plume of moisture prompting NWS to issue a WINTER STORM WARNING for the Mogollon Rim and North. This advisory started at 11:00 am Monday February 27th, lasting for 24 hours.
12 to 24 inches of snow, with 2-3 inches of snow water equivalent (SWE) is expected to fall on locations near and above treeline. Snow distribution and accumulation patterns will be influenced by winds out of the southwest in the 40 mph range during time of peak intensity. The freeze line will start high at 6500-7500' elevation and drop to near 5000’ by the storm’s culmination.
AVALANCHE DANGER WILL INCREASE. The heaviest precipitation is expected between midnight and daylight Tuesday morning. Storm snow and Wind Slab avalanche danger is expected to rise rapidly. Starting early Tuesday morning February 28th, natural avalanches will become possible until new snow blonds with old; and human triggered avalanche will be likely. Winter travelers are advised to stay out of avalanche terrain for at least 24 hours in the aftermath of heavy precipitation. Northeast and east facing slopes will become particularly hazardous, loaded by southwesterly storm winds.
In the aftermath of the storm, on Tuesday night, high elevation winds are expected to shift to northwesterly, gusting into the mid 30s mph, preceding a clear cold trend.
East and southeast facing slopes may receive further loading from post-storm transport of fallen snow, further increasing danger in those zones due to the northwesterly post-storm winds. Wind slabs have been found on every aspect this season: be alert for loaded areas near ridgelines and crossloaded terrain features; hollow sounding slabs, and fracturing or whumpfing in the snowpack.
By Friday, March 3rd, temperatures are expected to climb above freezing near treeline. Newly formed storm and wind slabs may become more reactive with warming conditions, especially on sun affected terrain.
Near and Above Treeline:Careful snowpack evaluation, cautious route-finding and conservative decision-making will be essential. Natural avalanches possible; human triggered avalanches likely. Stay away from steep terrain (>30°) and known avalanche paths until new storm and windslabs have time to bond.
Watch for wind loading below ridgelines, and cross-loading in chutes below the ridge lines.
Below Treeline:Tree skiing below treeline will be your safe bet. Avoid steep gully terrain traps and avalanche path run out zones.
New snow may create storm and wind slabs, especially above treeline. Even with light precipitation amounts, wind can deposit significant amounts of snow on leeward slopes, as well as cross load gullies and chutes. Wind slabs usually stabilize in less than a week. Reduce your exposure to avalanche hazard by waiting several days after a big loading event.
Always keep in mind, wind slabs are unpredictable, and may support the weight of a skier or rider initially, and fail suddenly with tragic consequences. Avoid snow surfaces which are recently loaded, sound hollow, have signs of fracturing, cracking, or whoompfing sounds.
New storm slab and wind slab development is very likely. Natural avalanches possible; human triggered avalanches likely. The development of near surface facets at the boundary of new and old snow could turn a storm slab concern into a persistent slab problem.
This season numerous rescues have been conducted by Coconino County Search and Rescue, and the Arizona Snowbowl Ski Patrol. Some of these could have been avoided by better planning and preparation.
Travelers are advised to exercise caution, make slope specific evaluations and most of all, know where you are going and be prepared for the unexpected.
As always, please treat this summary with appropriately guarded skepticism, make your own assessments, and contribute to our body of knowledge by reporting your observations.
Arizona Snowbowl uphill policy.
Want to learn more safe backcountry habits? KPAC offers level I and II avalanche courses. There is one class left this season.
During winter, backcountry permits are required to access the Kachina Peaks Wilderness. More info
Monday, February 27, 2017 update.
NWS, Flagstaff, AZ
Winter storm warning in effect until Tuesday, Feb. 28, 11am. 12 to 24 inches of snow, with 2-3 inches of snow water equivalent (SWE) is expected to fall on locations near and above treeline.
Last updated on Friday, February 24, 2017
Normal seasonal temperatures, and variable gusty winds out of the south-southwest and west followed the President’s Day weekend storm. Wind velocities exceeded 30 mph on Wednesday February 22nd and shifted to a northerly direction on Thursday and continued ever since. Cold temperatures and wind chill to -18° F was reported at the Agassiz Peak Station on Friday morning February 24th. Light precipitation will return to our region on Sunday, Monday and Tuesday accompanied by strong winds out of the west and southwest, as a series of short wave disturbances pass through. These appear to be lacking in moisture and are not expected to deliver more than a few inches of snow at higher elevations. Mostly clear skies and near normal temperatures will prevail for the rest of the week.
On the morning of Friday, February 24th the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 76 inches (193 cm) at 9700’, and Arizona Snowbowl reported 92 inches (234 cm) at 10,800'. These values are expected somewhat to increase as precipitation starts to fall during the weekend and into next week. Since February 17th SNOTEL temperatures ranged between 13° and 47° F and Agassiz station between 0° and 34° F.