Over the weekend new snow and wind will increase the avalanche hazard. Human triggered storm and wind slab avalanches will be possible and may become likely near and above treeline. Natural avalanches may be possible as wind transports new precipitation above treeline.
Avoid convex pillows of wind-drifted snow, watch for new wind slab development and avoid overhanging cornices that have formed on leeward sides of ridgelines. Cornices on February 25th. Another system may enter the area approximately Wednesday, March 6th and may keep avalanche hazard elevated.
Rapid warming after storms, or rain on snow may lead to wet avalanche activity. Evidence of a smallish wet avalanches were observed on sunny slopes near and below treeline the past few days. We've seen evidence of wet unstable snow on all steep slopes below 9,500'.
Between February 13th and 26th the snowpack roughly doubled. On those dates respectively, we measured ~150cm and ~300cm of snow on an ESE slope at 12,000' near Rustler Peak. Read more about our February recap.
Early February Storm Cycle:
Snowslide SNOTEL (9,730') reported 20" of new snow and ~3" of snow water equivalent (SWE) between Feb. 2nd and 6th. This resulted in a large avalanche in Snowslide Canyon on Feb. 5th or 6th. Classification is HS-N-R4D4-O. On Feb. 9th a crown line was observed about 1/2 way down Jay's Slide - a NNW aspect on Fremont. This avalanche likely occurred on Tuesday or Wednesday, February 5 or 6. Estimated classification is U-N-R2D2-U.
St. Valentine's Storm:
Heavy dense snow with rain levels near treeline. Snowslide SNOTEL reported 5" of new snow and ~2.5" of SWE between Feb. 14th and 15th. No avalanches observed. New hard/icy crusts in the snowpack.
Presidents Day Weekend Storm:
Snowslide SNOTEL reported 9" of new snow and ~<0.5" of SWE between Feb. 17th and 19th.
This resulted in small storm and/or wind slab avalanches on Rustler peak. Evidence observed on Feb. 20th. Though not big, these may have been large enough to injure and bury a person. Estimated classification for each is is U-N-R2D1.5-U (35.338, -111.683, ~E aspect). The hard Valentine frozen rain layer was a likely bed surface.
Feb. 21/22 Storm:
Snowslide SNOTEL reported 20" of new snow and ~1.4" of SWE between Feb. 20th and 22nd. This resulted in loose snow avalanches triggered by skiers, boarders, and natural small cornice drops. No significant slab avalanches observed.
March 11 update:
An old crown line and avalanche debris were discovered in the Telescope Chute of Doyle Peak. The crown was located at ~10,900' at a choke where the path briefly narrows and steepens. Avalanche debris and small broken trees were found at ~10,400’. This avalanche likely happened during the Feb. 21/22 storm.
Near and Above Treeline:Watch for new wind slab development and growing cornices on leeward slopes. Expect to find wind scoured zones and hard icy snow above treeline - especially on south , southwest, west and northwest slopes. Crampons and ice axes will help prevent falls on steep icy slopes.
Sunshine after storms may destabilize southerly and sunny slopes.
Below Treeline:Watch for rain on snow events, and warm temperatures destabilizing the snowpack.
Tree wells are getting deep and tree well immersion suffocation is a real possibility. Coverage is good on most slopes above 9,500', with plenty of safer low angle (<30°) touring.
New snow slabs and wind slabs will be your primary problem near and above treeline this weekend and next week.
Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Avoid slabs and convex pillows of wind-drifted snow on lee and cross-loaded terrain features.
Forecast calls for new snow and southwest and west winds this weekend, so watch for northeast and easterly wind slab formation. Also, chutes and gullies on other aspects may cross load.
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.
Waiting at least 48 hours after wind events will decrease your chances of finding unstable storm/wind slabs.
Avoid standing on overhung cornices, as they may collapse unpredictably and send you downslope. They can sometimes break far back on flat ridge-top terrain. Sunny warm weather can naturally release cornices.
Evidence of smallish wet slab avalanches were observed this week on southerly slopes below treeline. Current trend is towards cool and cloudy weather, but when warm weather returns, watch for loose wet and wet slab avalanche potential - primarily on steep southerly and westerly slopes above 10,000'. This could also become a problem on all steep aspects at elevations below 10,000 feet. Rain on snow will destabilize the snowpack on any aspect or elevation.
During warm weather, surface snow will become saturated with water. Deteriorating riding conditions (sticky slush) and rollerballs are an indication that you should move to a colder slope.
Read more about spring travel strategies.
We are getting close to the spring equinox and it is time to start thinking about spring travel strategies.
On Thursday, February 28th a fracture was observed in Telescope Chute, a northeast aspect of Doyle Peak. This appears to be a glide crack or an old avalanche crown. March 11 update: We confirmed that this was a crown line. See Overall section.
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 update Friday March 1st.
During the past week we have seen a gradual warming trend, high clouds, but no precipitation. By the time of this report, Temperatures have returned to near normal with daytime highs in the 30s at treeline. In the aftermath of last week’s mega storm, winds out of the north and northwest were observed Saturday February 23rd and to a lesser degree on Sunday and into the workweek. On Saturday Feb. 23rd, wind speeds ranged from 15-30 mph with gust in the 40 mph range out of the north and northwest. Breezy conditions returned on Thursday Feb. 28th and Friday Mar. 1st. These were in the 20+ mph range with stronger gusts out of the west and southwest.
During the upcoming weekend, another low pressure system will pass through. Current forecast is for 10 to 18" of snow near treeline, and a snow/rain line near 8000'. This storm will be accompanied by breezy conditions out of the southwest. During the following workweek, the weather will return to near normal temperatures and breezy days. Another storm my enter the area around mid-week, but it's too early to accurately predict anything about timing, intensity or storm track.
On Friday, March 1st, the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 63” (160cm) at 9,730'. Arizona Snowbowl reported a settled base of 98” (249 cm) at 10,800'. So far this winter, 278" (706 cm) of snow has fallen at the mid-mountain study site. Since February 23rd, SNOTEL temperatures have ranged between 8° F on February 24th, and 46° F on March 1st. For the same period, ASBTP (11,555') reported temperatures between 1.6° F on Feb. 23rd, and 35.7° F on March 1st.