Wow what a February! The first week of Feb. produced an avalanche cycle on the 5th or 6th. Saint Valentine delivered at least 2.7" of SWE - including rain and high density snow with a snow/rain line that pushed 11,000 feet. Then President's Day weekend delivered ~21" of light champaign powder. Now a winter storm warning is in effect through Friday.
Yesterday we observed evidence of a storm/wind slab release near Rustler Peak. Read more below.
Overall the snowpack structure has become quite complex, with huge variability and uncertainty. Many observations reveal a snowpack with poor structure, good strength and little to no reactivity. Others show potential failure energy hidden in persistent weak layers. And some observations even show good structure. Recent column tests on southwest slopes above 11,000' reveal continued persistent slab problems.
With the current forecast of 2-3 feet near treeline, avalanches may become very likely on Thurs/Fri, Feb. 21/22 . Cold temperatures and wind may keep the avalanche hazard elevated through the weekend.
Avoiding avalanche terrain during and 24 hours after powerful storms will significantly decrease your likelihood of triggering an avalanche. Also avoid convex pillows of wind-drifted snow on lee and cross-loaded terrain features.
Read more about recent avalanches.
Storm and/or wind slab avalanches released on Rustler peak. Evidence observed on Feb. 20th. Though not big, these look large enough to injure and bury a person. (35.338, -111.683, ~ENE aspect)
Large avalanche in Snowslide Canyon on Feb. 5 or 6. Characteristic classification is HS-N-R4D4-O
There was a crown line about 1/2 way down Jay's Slide - a NNW aspect on Fremont. Picture from Sat. Feb 9, 2019. This avalanche likely occurred on Tuesday or Wednesday, February 5 or 6. Estimated classification is U-N-R2D2-U.
Near and Above Treeline:Prior to the Valentine and President's Day storms, wind scoured zones reduced the snowpack down to bedrocks on some southwest, west and northwest slopes.
The warm and windy St. Valentine storm has created a hard and icy layers. Avalanches will likely initiate in newer snow above these layers, but could potentially step down into deeper persistent slab problems, creating larger and more destructive avalanches. The hard Valentine layers may act as a sliding surface for failures above. Icy Valentine layers may send you on an uncontrolled slide, crampons and ice axe may be helpful.
Unfortunately, we have not had a chance to observe/test northerly and easterly slopes. It would be best to minimize that uncertainty before committing to steep northerly and easterly slopes, and take note of the recent Rustler Peak avalanches (see below).
North, northwest and west-northwest winds blew Tuesday night through Wednesday morning - watch for wind slabs on south, southeast and east aspects. Winds shifted to the south this afternoon. Southwest winds are forecasted over the next 48 hours. Watch for slab development on east, northeast and northerly slopes.
Cornices are forming on the lee side of ridgelines. Avoid cornices, as they may collapse unpredictably and send you downslope.
Below Treeline:With the big storm forecasted, conservative terrain choices will be essential. Avoid avalanche path runout zones and terrain traps 24 hours after big storms.
Coverage has drastically improved! You will find great skiing and riding on low avalanche hazard slopes if you stay off of and out from under slopes that are greater than 30° in steepness. Low elevation (<9000') slopes are filling in.
To avoid these, wait 24 hours after the storm ends before you get into steep (>30°) terrain.
Rocks are getting covered above treeline and new storm snow may struggle to bond with the cold President's Day snow. Storm slabs commonly form during periods of light or no wind. The President's Weekend Storm had little wind.
New snow may also fail as unconsolidated point (loose dry) releases. Storm slabs and loose dry releases are generally small and harmless but may become dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
The bullseye slope angle for avalanche activity is 38 degrees. Moderating slope angles to 30 degrees and less drastically reduces the likelihood of triggering an avalanche. Storm slabs tend to stabilize relatively quickly. Waiting at least 24 hours after significant storms is always prudent. Waiting longer is even better.
Avoid convex pillows of wind-drifted snow on lee and cross-loaded terrain features.
South and southwest winds are forecasted over the next 24 hours then switching to the west-northwest.
Post storm winds may create slabs on other aspects. As always watch for cross loading in gullies. Slopes just below ridges and on the flanks of shoulders should be considered suspect.
Cornices are starting to form on the lee side of ridgelines. Avoid cornices, as they may collapse unpredictably and send you downslope.
Keep an eye on the ASBTP weather station. Readings between 15 and 35 mph indicate the potential for snow transport and formation of wind slabs. Look for various links under the weather menu above. Note that this station may get rimed during storms and report erroneously.
Give new snow time to bond with the old snow. Waiting at least 24 hours after new snow, and 48 hours after wind events will dramatically decrease your chances of finding unstable storm/wind slabs.
We continue to find evidence of persistent slab problems. The problem is not wide spread, but any medium to large steep slope or bowl near treeline should be considered suspect.
Watch for near surface facets above and below the hard Valentine's day layers. Also, basel facets may still be reactive, especially where the snowpack was less than 1.5m deep prior to the President's day storm.
New significant storm and wind slabs may cause persistent weak layers to fail. Worse, new slabs may push deep hidden weak layers just to the brink of failure, waiting to be triggered by an unsuspecting backcountry traveler.
Recent column tests on southwest slopes (Temptations) above 11,000' reveal continued persistent slab problems.
This problem led to the large Snowslide Canyon avalanche that naturally released on an easterly aspect near 12,000', the first week of February.
The December facet layer is getting buried quite deep now and will be very difficult to predict and manage.
See our courses page to register for a class and get avy savvy.
Backcountry permits are required for travel in the Kachina Peaks Wilderness and available at local USFS locations, as well as, at the Agassiz Lodge on Saturday and Sunday 8:30 -11:30.
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.
Weather updated February 20th.
The President's Day storm delivered ~21" of light champaign powder at 10,800'. Winds were calm and light. North, northwest and west-northwest winds blew Tuesday night through Wednesday morning, Feb. 20th. Winds shifted to the south this afternoon, Wednesday.
A major winter storm will bring widespread and significant snow Thursday into Friday (Feb. 21/22). Treeline totals may push 3+ feet of accumulation. Quieter weather returns for the weekend with continued below normal temperatures.
On Tuesday, Feb. 19th, the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 58” (147 cm) at 9,730'. Arizona Snowbowl reported a settled base of 84” (213 cm) at 10,800'. So far this winter, 212" (538 cm) of snow have fallen at the mid-mountain study site. Since February 15th, SNOTEL temperatures have ranged between -8° F on February 19th, and 33° F on Feb. 15th. For the same period, ASBTP (11,555') reported temperatures between -3° F on Feb. 1tth, and 23° F on Feb. 15th.