New Snow poses renewed avalanche problems. Prior to the Thursday January 9th evening storm, accumulated evidence has suggested that human triggered avalanches were generally unlikely. Many surfaces above treeline were stripped with multiple high wind events in recent weeks. Surfaces ranged from very firm on wind affected aspects above treeline to breakable crust on sunny aspects and some pockets of soft snow on northerly slopes. However, Thursday's storm has brought 9 inches as of January 10 on top of these previous surfaces. Remember, yesterday's snow surface can be today's weak layer or bed surface.
Pit data from January 4th through Friday, January 10th has continually suggested a complex, weak structure in the snowpack without significant energy on many aspects. Some pits have shown propagation propensity but this has, thus far, shown to be inconsistent indicating pockets of energy in the snowpack. The structure of the snowpack has remained consistently poor, particularly on northerly aspects. Weak layers surrounding several ice lenses have been persistent, particularly where the snow temperatures remain cold.
As more snow falls, be particularly cautious of wind transport and loading as strong north winds transport the new snow, creating wind slabs on leeward aspects, particularly above treeline. Most avalanches occur within 24 - 48 hours of new snow or a wind event. Persistent weak layers always have the potential to become reactive under new load.
Arizona Snowbowl is reporting 9 inches of new snow at 10,800', Friday, January 10th.
Look for new weak layer formation in the snowpack as deeper weak layers may start to heal. Near surface faceting is possible where melt-freeze crusts formed last week. Look for these new weak layers when evaluating the snowpack and their subsequent stability. Southerly Slopes also have potential wind load from north wind on Friday, January 10. As is often the case, however, wind on the Kachina peaks can move in many different directions locally. Evaluate local terrain for evidence of recent wind transport and be suspicious of leeward aspects from slopes that were stripped of new snow.
We currently have a complex snowpack that is highly variable depending on aspect and elevation. Review the snowpits.
Near and Above Treeline:Some aspects, such as the easterly aspects of the Humphrey's cirque and Snowslide bowl, have up to 3m of snow while other aspects above treeline were either stripped or packed down by wind to a very firm surface. Crampons are strongly recommended for mountain travel as the surface conditions were firm and highly variable prior to the January 9-10 storm and with wind are likely to remain so.
Leeward aspects (south and east) from the forecast north and west winds after the storm could have wind slabs overwhelming weak layers both new and old soon after the event. Suddenly 9 inches of new snow is available for wind transport. Carefully evaluate what wind has transported in the area of your intended travel and it's affect on the local snow stability.
Beware of wind transport. Wind can transport snow many times faster than falling snow. Manage terrain and evaluate snow stability carefully as the dust settles from this recent snow and subsequent wind.
Below Treeline:Surfaces below treeline prior to the storm ranged from firm to soft to breakable crust. Even with new snow, skiing is likely to be variable from turn to turn. Travel with care and watch for obstacles unseen from new snow. Sloughing is possible, particularly on aspects with a very firm surface prior to the new snow.
Beware of obstacles and highly variable conditions around the mountains below treeline.
Some avalanche danger may exist from wind slab on leeward slopes after the January 10th storm and north wind event. Look for signs of recent wind loading and pay attention to aspect and local wind loading patterns while traveling through the mountains. While South and East aspects are more likely to be loaded, local wind variations can lead to loading on almost any aspect. Evaluate terrain carefully.
Storm Slab releases are possible on aspects not stripped by wind 24-48 hours following the January 9-10 storm producing 9 inches of new snow. This may particularly be true on surfaces that were very firm prior to new snow.
Sloughing is possible on all aspects in the immediate time frame after the storm. New snow appears to be very light and unconsolidated.
Submit your observations here. You may save a life! The link to this form is now on our home page and snowpack menu.
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 January 10th
Last week’s weather was a mixed bag. A broad, low amplitude trough parked over the region allowed quick moving, short wave, low pressure systems to track through northern Arizona. These have brought wind, cool temperatures, and overcast skies, but not much precipitation. Between these events above average temperatures were recorded. At high elevations, temperatures in the mid 40° F have created melt/freeze crusts on most sunny aspects. Nighttime temperature inversions were also evident during these periods. On Thursday afternoon and night, one of these short wave lows brought moderate winds out of the southwest and 9+ inches of new snow at 10,800 feet.
Looking forward, it appears that an alternating pattern of unsettled weather and pleasant conditions may persist. Windy, cold weather is predicted for the weekend with below zero wind chill temperatures. Snow showers, but not much accumulation are in rhe forecast for mid-week. If the broad trough breaks down, we may return to a more productive precipitation pattern.
Arizona Snowbowl reported a 61” (155cm) base at 10,800 feet. Snowslide SNOTEL reports a 48” (122cm) snow depth. So far this winter, we have had 138” (350cm) of snowfall at 10,800 feet.
Since January 3rd, SNOTEL temperatures have ranged between 15° F on January 6th and 43°F on January 4th. ASBTP station (11,555 ft) reported a low of 11° F on January 9th and a high of 43° F on January7th.