The first week of February brought a 50 degree temperature range on the Kachina Peaks along with variable winds. Earlier in the week southwest winds were followed by stronger northeast wind and colder temperatures on Feb 5-6. After days of sunny weather and warmer temperatures, several melt freeze crusts have developed on all aspects with varying degrees of thickness and hardness.
Overall, the snowpack is demonstrating a complex structure, moderate to good strength, and low reactivity. New precipitation, wind loading, and near surface facet growth could alter this equation to higher instability with a storm forecast for Monday.
Wet avalanche activity remains a possibility this weekend, with high temperatures forecast, particularly on southerly aspects. There was one report of a relatively small skier triggered wet slough in the Humphrey's Cirque on Saturday, February 1 (see photo below).
While some older weak layers have been showing evidence of bonding with prolonged warmer temperatures, the possibility for near surface faceting remains with newly formed crusts as colder temperatures return to northern Arizona. Pay particular attention to the temperature profile as a large temperature gradient over a short distance can signify weak facet layer formation and progressive instability. This could become particularly relevant if new snow falls as forecast for the week of February 10.
The last slab avalanches noted on the Kachina Peaks were during and after the Christmas 2019 storm cycle.
However, this weekend presents a great opportunity to observe the snow surface and snowpack in detail before next week's forecast snow. Watch for wet slides if temperatures are high and observe the snow surface and structure carefully before the upcoming storm. Yesterday's snow surface can become tomorrow's weak layer or bed surface.
Sloughing from any new snow this next week is possible on firm frozen surfaces. If more significant amounts of snow were to fall this week, 8 inches or more with wind, there is potential for current near surface facets become a significant weak layer under storm slab and wind slab. Pay attention to this week's weather.
Near and Above Treeline:Moderate wind, out of the southwest shifting to the northeast in the last week, has stripped some aspects above treeline while rendering others wind loaded. Always be cautious of wind slab formation on steep, leeward slopes. Observe for local signs of wind stripping and subsequent loading on leeward aspects wherever you travel above treeline. Ice axe and crampons are strongly recommended as surface conditions can be very firm depending on the time of day and temperature. Be prepared. Where wind has not scoured snow, depths remain at 1-2 meters.
Below Treeline:High daytime temperatures could contribute to decreased stability on sunny slopes over the weekend. With a decrease in elevation comes a decrease in snow depth. Obstacles become the main hazard below 9000 ft but are present on all aspects at all elevations. Expect the unexpected. As snow falls throughout the week many of these obstacles may become covered but still be hazardous. Ski and snowboard with care after new snow.
When daytime temperatures warm, stability on sunny aspects may deteriorate. Observe carefully and remember that timing is important. Loose wet avalanches generally become more likely as the day goes on. One relatively small wet slough, pictured below, was reported on Saturday Feb 1. Manage terrain and tour plans according to weather.
Approach high elevation, leeward ridge lines with caution. Leeward sides of gullies and spurs may hold pockets of cross-loaded unstable wind slab. Beware of wind drifts in steep terrain. Hard slabs are most prone to human triggering where they are thin/weak, and therefore, more susceptible to failure under a person's weight.
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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.
Updated Friday February 7
A wonderfully warm Groundhog Day weekend was replaced by a cold trough passing to our north. Originally predicted to deliver at least a few inches of new snow, we received only bone-chilling winds out of the southwest and the coldest temperatures of the winter. High temperatures in the low teens and sub 0° F lows were recorded at treeline. Windchill temperatures at ASBTP (11,555’) dropped into -20s Fahrenheit.
Windy and frigid conditions were followed by warming to above average temperatures on Thursday, with generally fair and intermittent breezy weather forecasted through the weekend. We have been experiencing a persistent dry pattern with occasional mid-latitude short wave troughs to the north.
Our next chance for precipitation, and a possible pattern shift will arrive early in the workweek, hopefully as a significant winter storm. Interactions between a cutoff low pressure system, the arctic, and the sub-tropical jet streams may draw in sufficient mid-level moisture to support significant high elevation snowfall. We are looking at this complex interaction of meteorological elements with guarded optimism. Let’s keep our collective fingers crossed. Unsettled weather will characterize much of the upcoming week.
Arizona Snowbowl reported a 52” (132cm) base at 10,800 feet. Snowslide SNOTEL reports a 44” (112cm) snow depth. So far this winter, we have had 145” (368 cm) of snowfall at 10,800 feet.
Since January 21st, SNOTEL temperatures have ranged between -7° F on February 4th and 50° F on February 2nd. ASBTP station (11,555 ft) reported a low of -5° F on February 4th and a high of 47° F on February 1st.