Flagstaff, Arizona - Backcountry of The San Francisco Peaks and Kachina Peaks Wilderness
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With the forecasted warm temps and unsettled (windy and snowy) weather, human triggered avalanches will be possible.
Wednesday through Saturday (March 10-13) a slow moving low-pressure system brought ample precipitation and light to moderate southwesterly winds. The storm total reported by AZ Snowbowl (10800') was 41", with SNOTEL (9730') reporting a storm total of 27" and 2.5" of snow water equivalent. Post storm moderate to strong winds blew from the north, then early Tuesday (March 16) a quick moving shortwave through brought 10 more inches to 10800'.
Evidence observed on March 18 indicate that this mid-March storm cycle contributed to at least two natural avalanches. Debris (obscured by subsequent snow) was observed on a southeast aspect near treeline - see photo below. This avalanche was estimated as SS-N-R1-D2-U. Debris was also reported near/below treeline on a northerly slope of Core Ridge.
The spring equinox occurs Saturday, March 20, 2021.
Steep northerly and shaded slopes still have some powder available for transport. Forecast calls for winds as well as light snow on March 20, 23 and 24. Watch for new wind slabs on leeward aspects above treeline.
Small loose wet avalanches were observed on warm sunny slopes near/above treeline on Thursday, March 18. Warming temperatures have created a melt/freeze surface on many aspects above treeline. Steep, sheltered and shady northerly slopes still have powder snow.
Warming temperatures have resulted in rapid settlement of the new snow (especially below 10,000'). Expect a melt/freeze surface on most or all slopes below treeline. Watch for warming on steep slopes becoming saturated and unstable.
A typical springtime warming cycle is in progress at lower elevations where the snowpack is becoming more uniform in temperature gradient (isothermal), and avalanche concerns are either related to melting (wet slides), or to poor bonding between new snow and old snowpack.
With the new snow, approaches and egresses have improved, but the warm temps of the past few days are quickly melting the coverage at lower elevations and sunny aspects.
There is some powder snow (on northern near/above treeline aspects) available for transport. With more snow and winds in the forecast, the building of new wind slabs will be possible.
The Spring Equinox occurs Saturday, March 20.
Current forecast indicates a breezy and cooling trend, so this problem will probably become unlikely in the short term. But when sunny, spring weather returns, watch for warming temperatures creating wet saturated slopes. These will be most evident near exposed rocky outcrops on sun baked slopes.