Northern New Mexico

Today you can trigger a dangerous avalanche where new snow has formed a cohesive slab on aspects that held snow prior to yesterday's storm, which are primarily North and East aspects.  This storm added a significant amount of weight (1.2-1.4") to our weak, shallow snowpack, overwhelming facets and depth hoar that have formed during the dry winter we've had.  As you move up in elevation, there is the potential for larger avalanches that break wider and take most of the season's snowpack with them.

Be on the lookout for smaller instabilities in the storm snow today, and be very cautious if you're getting large audible whumpfs or shooting cracks.  Stay off and out from underneath large steep slopes today, as these conditions lend themselves to remote triggering. 

Yesterday's snow totals weren't outrageous, but the storm came in warm, wet, and windy, dropping a cumulative 1.2-1.4" SWE in the Northern Sangres, overstressing our predominantly weak snowpack and leading to very dangerous avalanche conditions yesterday.  The storm has cleared significantly since yesterday evening and the winds will ease to moderate today.  We picked up another dusting of snow early this morning and could squeeze out a few more inches of snow by the end of the day before the upper level trough makes a full exit.  While peak instability has passed for this storm, the avalanche danger is Considerable today at all elevations.  Please be careful and make conservative decisions if you're getting out there this holiday weekend, as avalanche terrain remains a dangerous place to be on or near today.  Here is why.

Extremely weak snow pervades the Northern NM snowpack after 3 months of weather dominated by drought and shallow overall snow depths.  Large facets and depth hoar crystals can be found all throughout the oldest parts of the snow that date back to November 8th, and in many cases the more recent snow as well (though there isn't a whole lot of that).  Easterly and northerly aspects that have held snow this long show up until this last storm show this trend the most dramatically, and the weak snow has not showed signs of healing even with record-breaking temperatures in early February.  Below treeline, these weak layers are fairly close to the snow surface and easiest to impact as a traveler, and we were able to confirm this in our travels yesterday with several large collapses that extended widely across slopes.  At higher elevations, greater exposure to the sun and recent strong winds have built and sustained melt-freeze crusts and hard slabs on or near the surface, and the faceted weak layers are a now a bit further down.  These areas can hold a bit more of the weight from this last storm but are still struggling to adjust to the new load.

Here's Andy giving an overall picture of the Northern NM snowpack, highlighting the differences in elevation and the expected impacts of yesterday's storm.  The storm turned out fairly productive, dropping a cumulative 1.2-1.4" SWE with strong winds, building out slabs and overstressing weak snow near the ground on many slopes. 

We were able to get out and observe some of the impacts of yesterday's atmospheric river event in below-treeline terrain.  We observed about 4-8 inches of higher density new snow forming fresh slabs during the peak hours of the storm, with plenty of variability from place to place thanks to the intense and swirling winds.  This snow fell onto a variety of surfaces ranging from near surface facets to melt-freeze crusts, to bare ground.  Lots of graupel fell during the storm as well.  We had widespread cracking and collapsing while walking around on these fresh slabs, and found plenty of evidence of recent natural avalanches that failed during the storm.  These were all clear indications that we had a sensitive storm slab problem during yesterday's event, and we expect these storm slabs to remain reactive today.  The setup is there: these slabs could fail at the old snow interface on near surface facets or on layers of graupel within themselves.  Expect the size and sensitivity of the storm slabs to be variable across short periods of space today with the sheer amount of wind that blew yesterday, but also expect them to get larger and thicker as you move up in elevation, where the most snow fell and the most wind blew.

This brings me to the heart of the dicussion: our persistent slab problem.  1.2-1.4" SWE is the most weight we've added to our widespread weak layers all season, and this will make human-triggered persistent slab avalanches likely today.  Yesterday, I was able to get several longer shooting cracks and even remotely triggered a small (D1) slab avalanche from 100 feet away, which I'm confident propagated on depth hoar.  These kinds of avalanches will be easiest to trigger below treeline and at lower elevations that didn't hold much of a slab prior to yesterday's storm, but they will also be relatively smaller.  As you move up in elevation into terrain that harbored a hard slab or melt-freeze crust(s), the potential avalanches will be larger and break deeper, but they will also be harder to trigger.  Places like the one in Andy's video above are somewhat of a sweet spot of size and triggerability, but many of these slope may have run naturally during the storm -- it's hard to say as we didn't get very good visibility yesterday.  Nonetheless, this avalanche problem is the most dangerous that we currently face and it's worth approaching it with serious caution over this holiday weekend.

If you're getting out into the backcountry today, keep it simple and stick to a conservative tour plan.  Carefully evaluate the snowpack and back off as soon as you get the sure-fire signs of instability like loud audible collapses or big shooting cracks.  Be cognizant of the potential for remote triggering today, meaning you might be standing on relatively flat terrain but could trigger an avalanche above you.  It's best to give large steep areas or known avalanche paths a wide berth.  The good news is that travel conditions will start to improve drastically in the wake of this storm and with maybe a few more inches falling over the course of the day.  Enjoy this fresh blanket of snow on the mountains over President's Day Weekend and stay safe!