THIS AVALANCHE ADVISORY EXPIRED ON March 7, 2017 @ 5:43 am
Avalanche Advisory published on March 6, 2017 @ 5:43 am
Issued by Andy Bond - Taos Avalanche Center

MODERATE avalanche danger continues to exist above and near treeline today, where human triggered persistent slab avalanches remain possible.  Weak, faceted snow underlies a persistent slab on many slopes, requiring careful evaluation of each slope independently.  Identify slopes and features of concern and manage terrain choices accordingly. LOW avalanche danger exists below treeline as these slopes have gone through melt-freeze cycles and colder temperatures are forecasted for today. 

2. Moderate

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Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
  • 1. Low
  • 2. Moderate
  • 3. Considerable
  • 4. High
  • 5. Extreme
Avalanche Problem 1: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Triggering a persistent slab avalanche remains possible today near and above treeline.  In most places a 2 to 4 foot cohesive slab from the snow earlier this week is resting on top of facet crust combinations on solar aspects and a layer of buried near surface facets on northerly aspects. Stability tests are still indicating that these weak layers are still propagating with ease. Not every slope you ski or ride will avalanche, but if you find that "sweet" spot on the wrong slope you could trigger a large and destructive avalanche.  

Dig down in the snow and look for the presence of these weak layers, there pretty easy to identify right now.  It doesn't take much time, and is going to be the only way you're going to know if the slopes you plan to ski or ride are haboring this strong over weak snowpack structure.   

advisory discussion

MODERATE avalanche danger exists above and near treeline today, while below treeline areas have a LOW danger.  Remember a Moderate danger indicates that human triggered avalanches are possible.  A layer of low density factes is now buried by a 2 to 4 foot slab on many slopes at mid and high elevations. In some areas this weak layer of facets is associated with a smooth crust providing a nice sliding surface for that slab.  Stability tests are indicating that you can initiate collapse and propagation of this weak layer.  While the chances of triggering this slab will not be widespread, it is certainly possible, especially in shallow, rocky areas where the weight of a skier or rider is more likely to collapse the weak layer. Persistent slab problems are exactly that - persistent, and these weak layers take time to heal.  These conditions are capable of producing potentially large and destructive avalanches, and require careful evaluation of snowpack and terrain.  Dig down a few feet and see if this layer of facets exists on the slope you plan to play on, and see if it has a williingness to propagate.  The existance of a buried layer of facets underlying a denser slab should make us all travel conservatively, and carefully evaluate each slope with a fresh set of lenses.  We are back in the zone of "if you happen to trigger this slab, the consequences could be high".  

Today's strong west winds won't have much snow to transport as most west facing slopes are already void of transportable snow. Only an inch of snow is forecasted for today but if weather conditions change and we get more snow than forecasted, continue to reassess for isolated wind slabs as avalanche danger could rise.  I suspect the hardest part of today will be standing upright due to the strong winds.   

If you're interested in how much snow we've gotten this year check out our recent blog post.  This was written before this last storm, so add 25.5" of snow and 3.15" of SWE to the totals from February which should bring us right around average!

We have a fresh beacon problem out at TSV for the week of feb 28 - mar 6 - check it out and keep your beacon skills sharp!

If you get into the backcountry, please drop us a line at Taosavalanchecenter@gmail.com or on the "Submit Observations" tab at the top of the homepage.  Your field observations are extremely helpful, no matter how simple, and we thank all of you who have shared.

If you're looking to get some exercise and support a great cause look into the Ben Myers Ridge-A-Thon.  This event has been going on now for 20 Years. Come hike the ridge at Taos Ski Valley March 17 & 18th and raise some money that benefits our community!

recent observations

Not much has changed in the last couple of days as these nasty persistent layers continue to linger in the middle to upper portions of the snowpack.  Slab depths are deepest above treeline on North through East aspects, where we've found 4' storm slabs from last weeks storm and strong WSW winds.  Most of these slabs are 4 finger to 1 finger in hand hardness. Right now is a great time to practice Extended Column Tests (ECT) and Propagation Saw Tests (PST).  See video of Graham doing an ECT on a NE aspect around 11,800'.

Saturday was a warm, mostly sunny day in the mountains, with light to moderate winds.  Most of the windward fetches do not have much snow available for transport at this point, and we have not seen slab-building wind effects in most places the last couple of days.  Solar aspects had a crunchy surface sun crust, which broke down during the heat of the day.  No wet loose slides were observed.  Cold, dry snow has been preserved on the shadier aspects,  and our buried weak layers (2-4feet down) are not changing much with this weather pattern.

A regular observer found a layercake of weak layer/ crust combos while poking around SW aspects above Williams Lake on Saturday, but noted these layers were not overly reactive. His stability test results suggest this aspect is not as touchy as others, which is consistent with what we have been finding on West and Southwest aspects.

On Friday my partners and I toured up into Long Canyon to investigate the week's snowpack changes.  Check out the video.  We saw evidence of several fairly widespread natural slab avalanches that ran on a buried layer of facets and a crust/facet combo (see pic below).  We suspect these slides released Tuesday during the storm's peak instability, as the crowns are almost covered by subsequent snow, as shown in the photo below.  Propagation saw tests (PSTs) and Extended Column Tests (ECTs) were consistently showing the buried weak layer of facets are suspect, with sudden collapses and full columnar propagation the norm.  PST results were in the 30/100 cm range, and ECT scores were in the teens and low 20s, with full propagation.  We noted that while it would not be likely to trigger these slabs on all slopes, areas of concern are shallow, rocky rollovers and steep convexities.  Solar aspects were getting wet and just starting to pinwheel around noon and we avoided afternoon sunny slopes with respect to the chances of wet loose slides.

On Thursday Andy made this video explaining the slab/ crust situation in the higher elevations, where the weak layer is deeper in the snowpack.

Pic; An old crown from Tuesday or Wednesday on a NE Aspect around 11,400'.  These slides from Tuesday's storm had widespread propagation and ran on buried facets and crusts formed last week.  Most of the crowns are almost covered by subsequent snow, but are 2-3 feet in most places.

Pic; pit from Friday, NNE aspect at 11,700ft.  Buried weak layer of facets sitting below a 2 foot slab. PST 30/100 END SC More northerly aspects have no crust just buried near surface facets that formed before Monday's storm.

 

Pic: Snowpit from a North Aspect near treeline on Thursday.  The storm slab is 92cm thick with 4F to F hard snow.  I marked the weak lower density snow that is still there from Monday morning.  ECTP 15 SP where the line is marked.

Weather and CURRENT CONDITIONS
weather summary

A high wind warning warning is in effect for us today with Gusts as high as 70 MPH out of the west.  Temperatures will cool some with highs just reaching freezing around 9000'.  An upper level low will stay to our North bringing us strong winds and the chance of some light orographic snow (1 to 2 inches). 

Weather observations from the Wheeler Peak Wilderness between 9000 ft. and 13000 ft.
0600 temperature: 16.5 deg. F.
Max. temperature in the last 24 hours: 32.2 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 33 mph
Maximum wind gust in the last 24 hours: 79 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 88.3 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Albuquerque NWS
For 9000 ft. to 10000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy with chance of snow showers and patchy blowing snow. Mostly clear. Mostly Sunny.
Temperatures: high to 32 deg. F. low to 16 deg. F. high to 41 deg. F.
Wind Direction: W W W
Wind Speed: 20-40 20-35 10 - 30 decreasing to 10 - 20 in the afternoon
Expected snowfall: 0.2-0.8 in. 0 in. 0 in.
For 11000 ft. to 13000 ft.
Monday Monday Night Tuesday
Weather: Partly cloudy with chance of snow showers and patchy blowing snow. Mostly clear. Mostly Sunny.
Temperatures: high to 24 deg. F. low to 11 deg. F. high to 31 deg. F.
Wind Direction: W W W
Wind Speed: 30-45 15 - 40 decreasing to 15 - 30 after midnight 15-30
Expected snowfall: 0.2-0.8 in. 0 in. 0 in.
Disclaimer

This advisory applies only to backcountry areas outside established ski area boundaries, Click here for a map of the area. . This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the Taos Avalanche Center who is solely responsible for its content.