By Arden Feldman            CBAC Intern

The week consisted of three separate storms that kept clouds and snow in the air for most of the week. The first storm began on the night of the 19^th and continued through the afternoon of the 20^th. It brought with it low-density snow and very little wind, preserving and burying the surface hoar that had grown and had been observed on all aspects up to at least 12,000 feet in elevation. The western part of the zone received significantly higher snow totals with 24” of new snow reported in the paradise divide zone on the 20^th. Schofield received .7” of SWE and Mt. Crested Butte received .4” of SWE.

1/20/17 – Satellite image showing the first storm of the week impacting Colorado.

On the 21^st, the second storm came in lighter than forecasted and resulted in mostly light snow showers across the zone. Schofield received .3” of SWE. A small ridge then formed over the western US on the 22^nd allowing for a short break in the storm pattern. The third storm combined Pacific moisture and a strong upper level jet to hit our area ferociously on the 23^rd. We experienced extreme southwest winds and intense snow transport, even in town. During the day on the 23^rd, Scarp Ridge recorded consistent 60 mph winds and a maximum gust of 111 mph. Schofield received 2” of SWE and Mt. Crested Butte received 1” of SWE.

1/23/17 – Satellite image showing the windy third storm impacting Colorado.

From the 24^th through the end of the week on the 26^th, the third storm exiting to our east brought a northwest flow over our area causing light snow, generally broken skies, and cold temperatures.

This week’s snow buried a widespread surface hoar layer on all aspects along with a reactive faceted crust on southerly tilts. In the beginning of the week, the slab above it was too soft and thin for failures to propagate, but as the snow accumulated over the week, the slab grew and the surface hoar layer became very reactive. Numerous natural and skier triggered avalanches were observed failing on the surface hoar, even on low angle slopes, in relatively dense aspen groves, and as remote triggers. The avalanche danger was rated at considerable or high every day of the week other than the first day of the storm, Jan 20^th. In places, the surface hoar layer was deceptively touchy: we had several field days where it didn’t produce propagating results in ECTs but was easily triggered on steep terrain. The extreme southwest winds with intense snow transport likely created wind slabs in the alpine, but with continued snow transport and limited alpine views, evidence of them was likely quickly covered up. Over the course of the week, 39 natural and 37 human triggered avalanches were observed, and we had limited views of alpine terrain.

1/26/16 – Skier triggered avalanche on the surface hoar layer in an aspen grove.

1/26/17 – Skier triggered avalanche on the surface hoar layer that pulled out to a 31 degree ridge.

1/24/17 – Remotely triggered avalanches on the surface hoar layer with wide propagation.

1/24/17 – Natural avalanche on the surface hoar layer on a northeast aspect below tree line.

1/26/17 – Natural avalanche on a southeast aspect near tree line.

1/26/17 – Skier triggered avalanche on the surface hoar layer on a north aspect below tree line.

By Arden Feldman            CBAC Intern

The same cut off low from January 12^th continued to impact Colorado until the 16^th. It slowly meandered from Baja to the Arizona/Mexico Border and finally on to Texas while spinning multiple ripples of moisture into our area with increasingly less favorable atmospheric flow directions. This kept light snow showers and cloud cover over Crested Butte until the 16^th. Schofield received .5” of SWE on the 13^th and .4” of SWE on the 14^th. CBMR reported 3” of new snow on the morning of the 14^th, another 3” on the 15^th, and 1” on the 16^th.

1/13/17 – Satellite image showing the cut off low near Baja sending moisture into Colorado.

The weak trough slowly slid its way far enough east to allow for high pressure to build over Colorado on the 16^th. The high pressure lasted through the end of the week, allowing for the first major break in storminess in over two weeks. A pleasant reminder that the sun does in fact still exist! Although the sun was out at high elevations, impressive inversions created spectacular valley fog unusual for our area. Clear, calm nights allowed for widespread surface hoar growth. At the end of the week, on the evening of the 19^th, snow began to fall again, burying the surface hoar and making it our next problematic persistent weak layer.

1/16/17 – Unusual valley fog below Mount Crested Butte.

1/19/17 – Surface hoar sitting on top of a soft crust on a southwest aspect.

Last week’s historic storm left us with dense slabs, generally 3-5 feet thick, plastered across all aspects. These slabs are sitting on persistent weak layers at the storm interface and down near the ground. Clearing skies over the week finally gave views of avalanches that occurred during the storm cycle. Several large, natural deep slab avalanches, up to size D4, were observed. With the calm weather, avalanche instabilities slowly stabilized over the week. The deep persistent slab problem lurking in our snowpack was the main avalanche concern with storm slabs coming off the problem list by the 15th. The deep slab problem was slowly healing and represented a low likelihood but very high consequence event. No deep slab avalanches were reported occurring in our zone over the week but one deep slab did run naturally in the neighboring Aspen zone on the 17^th.

1/13/17 – CBAC Snodgrass Snow Study Plot profile showing the thick slab formed during the historic storm that is sitting upon healing weak layers.

1/16/17 – Extent of debris pile of D4 avalanche on northwest aspect of Scarp Ridge that destroyed mature timber.

1/16/17 – Partially filled in crown of D2.5 avalanche on an east aspect of Mt. Emmons.

1/17/17 – Crown of deep slab avalanche on northeast aspect of Cascade Peak.

1/17/17 – D3 deep slab avalanche that ran naturally on the 17th in the neighboring Aspen zone.

By Arden Feldman            CBAC Intern

The week started off dry and extremely cold with valley temperatures on the morning of January 7^th ranging from -25 to -35 F and mountain temperatures hovering just above zero. That weather did not last long as a very moist and warm air mass started infiltrating the area on the 8^th from the west-southwest causing snow showers to ramp up again after last week’s snow. This air mass continued flowing into the area from the Pacific through the 9^th bringing with it impressive amounts of precipitation and strong winds. With temperatures hovering right around the freezing mark, the precipitation fell as very wet snow. On the night of the 9^th a cold front passed over initially causing heavy snowfall and strong winds, but eventually allowing for a lull in the storm on the 10^th. From the 8^th through the 9^th Schofield picked up 5” of SWE and 26” of snow with 3” of SWE falling in a mere 16 hours on the 9^th. CBMR received 2.5” of SWE and 30” of snow. On the 9^th, the Crested Butte Community School closed for the first time since 1970 and CBMR closed early due to safety concerns. People were calling it the snowpocalypse.

1/9/17 – Satellite image from the National Weather Service showing the abundant moisture beginning to hit Colorado from the Pacific.

Staying true to its character, during the “lull” on the 10^th, the storm still brought in 6-8” of new snow and strong winds. Elkton had sustained winds of 16 mph and gusts up to 94 mph. On the 11^th we saw pacific moisture flowing into the area from the west-southwest yet again and another cold front passing over that night. This resulted in yet another pulse of heavy snow and strong winds. During this pulse, Schofield picked up 1.6” of SWE and 9” of snow and CBMR received 10” of snow. Elkton recorded sustained winds of 18 mph and gusts up to 76 mph.

On January 12^th a low pressure system off the coast of California began to sag towards Baja and cut off from the main atmospheric flow. The southerly flow of this cut off storm sent warm temperatures and one more significant plume of moisture into our area resulting in another 1.4” of SWE falling at Schofield.

1/12/17 – Satellite image from the National Weather Service showing moisture from the cut off low impacting Colorado.

Since January 1^st, the Gunnison Valley has been in the bull’s-eye for moisture from the Pacific. After that last plume of moisture on the 12^th, Schofield pass now stands at 14” of SWE since the storm cycle began on January 1^st. That makes this storm the largest in history since the Schofield Snotel was established in 1985! As of January 12^th, the Gunnison River Basin snowpack is at 166% of normal for this time of year. That means the snowpack is already deeper than it ever got during the 14/15 season, and it’s only early January!

1/12/17 – Gunnison River Basin snowpack summary showing our deep snowpack.

The week began with avalanche conditions beginning to stabilize after the previous week’s snow with considerable danger on the 7^th dropping to moderate on the 8^th. The impressive snow amounts that fell on the 8^th and 9^th added a large load to the snowpack, causing the avalanche danger to rise to high with an avalanche warning on the 9^th. With heavy snow and strong winds continuing through the week, the avalanche danger never fell below high. On the 11^th, an extreme (L5) avalanche danger was issued, a rare occurrence. Since 1985 we have only seen 4 or 5 events that met that criteria. In this case, the historic amount of snow that fell since January 1^st created a massive slab that was sitting on a number of persistent weak layers that were detailed in last week’s summary, including crusts, facets, surface hoar, and depth hoar. Very large storm slabs were also running. Both of these problems were forecasted to be widespread and large enough to run into valley bottoms and reach historic lengths.

With snow continuing to fall through the end of the week, we haven’t gotten good enough visibility to observe this storm’s avalanches out in the mountains. Still, we have had reports from across the state that indicate the historic nature of this storm with avalanches running across Taylor Canyon, I-70, and Red Mountain Pass, local roofs collapsing and historic mine structures demolished by avalanches. Locally, two avalanches ran across Kebler Pass road (first, second), a patroller was caught in a slide at CBMR, and many avalanches up to size D2.5 were reported even with our limited visibility. Large roof avalanches were also common in town.

1/9/17 – Natural D2.5 persistent slab avalanche on Red Ridge that ran to the ground in places.

1/9/17 – Crown of natural D2.5 persistent slab avalanche that ran across Kebler Pass Road.

1/12/17 – Debris of an avalanche that crossed Taylor canyon into a popular fishing hole. Definitely large enough to kill a fish!

By Arden Feldman            CBAC Intern

The New Year began with two low-pressure systems, one in the northwest, and another off the California/Baja coast creating a stream of moisture from the Pacific into Colorado. This produced 12-18” of low density snow across the area. CBMR reported 14” of snow and .3” SWE over the two days. Winds out of the southwest averaged 10-25 mph above tree line with gusts in the 50’s.

1/1/17 – Satellite image from the National Weather Service showing the two low-pressure systems, one in the northwest and another off the California/Baja coast. Clouds can also be seen beginning to form over Colorado.

The storm picked up in intensity from the night of January 3^rd through the 5^th. The jet stream lined up overhead producing a west-southwest flow and providing abundant moisture from the Pacific. By the morning of January 5^th, Schofield had received 3.7” of SWE and 30” of snow since January 1^st. On the 5^th, a powerful cold front slowly sagged south over Colorado and the Crested Butte area got pummeled with snow falling at 2-3” per hour rates throughout the day. After the cold front passed, measured storm totals since New Year’s Day were 5.56” of SWE and 57” of snow at Irwin, 5” of SWE and 41” of settled snow at Schofield, and 47” of snow at CBMR. Behind the front, colder, drier air moved in, leaving clearing skies and frigid temperatures in its wake for January 6^th.

1/4/17 – Satellite image from the National Weather Service showing the abundant moisture flowing into Colorado from the Pacific.

There were a number of problematic surfaces at the storm interface that had formed over the previous dry week, including near surface facets, surface hoar, melt-freeze crusts, and slick wind crusts. The storm created a sizeable slab that was sitting on those interfaces and persistent weak layers. The observed human triggered and natural avalanches grew larger in size as the storm progressed. Initially, there were touchy, relatively shallow storm slab instabilities, even with surprisingly low density and incohesive slabs. By the later parts of the storm, larger avalanches were failing naturally on these interfaces. The avalanche danger was rated as HIGH on both January 4^th and 5^th and a major natural avalanche cycle occurred with reports of many D2 to D3 avalanches around the zone. There was even some avalanche activity that 45-year locals had rarely seen.

1/3/17 – Skier triggered D2 storm slab on Schuylkill Ridge that failed on a surface hoar layer buried at the beginning of the storm.

1/6/17 – Natural D2.5 Persistent Slab avalanche on a southeast aspect of Purple Peak.

1/6/17 – Natural D2.5 persistent slab avalanche on an east aspect of Mt. Owen.

1/6/17 – CBAC Snodgrass Snow Study Plot profile showing the snowpack after this week’s major storm.

By Arden Feldman            CBAC Intern

From December 20^th to 22^nd, the snowpack continued to stabilize after the major December 16/17^th storm. Valley inversions dipped to -15 in town.

12/22/16 – CBAC Snodgrass Snow Study Plot profile showing the stabilizing snowpack after the December 16/17^th storm. 

A warm southwestern system impacted the Elks on 22^nd. The storm brought with it snowfall rates up to 2” per hour and 20-30 mph west winds above tree line. Schofield received 14” of snow and 1.3” of SWE and CBMR received 8” of snow and .8” of SWE. The avalanche danger rose to considerable at all elevations on the 23^rd and observers reported natural and skier triggered storm slabs.

On the 23^rd and 24^th, winds out of the south averaged 15 mph with gusts up to 64 mph at the Elkton weather station. These strong southerly winds created unusual loading patterns on north faces. For example, the north face of Ruby Peak had been wind scoured near to the ground during the 12/16 storm, but was reloaded by southerly winds, and produced two natural slabs, breaking 2-3 feet deep. A large slide also ran to the valley floor off of Gothic.

12/24/16 – Pair of 2-3 foot soft slabs that ran naturally on the north face of Ruby Peak, failing on old snow at the ground.

12/24/16 – Natural avalanche on northeastern aspect of Gothic Mountain.

A cold front brought snow and strong winds from the west on the 25th. 7-14” of snow fell across the zone with Schofield picking up 8” and .8” of SWE. The strong winds formed sensitive wind slabs on leeward slopes.

12/24/16 – Satellite image from the National Weather Service showing the Christmas storm on its way to Colorado.

12/25/16 – Small skier triggered wind slab near tree line on an easterly aspect.

The 26^th of December through the end of the year was characterized by dry conditions, with powerful southwesterly winds, cold temperatures, and strong solar radiation. Over this time period, the avalanche danger slowly fell. Wind slabs were a significant issue during the first part of this timeframe due to the strong winds and ample snow available for transport. The wind slabs did eventually heal and persistent slabs became the main avalanche concern. Although slowly healing there were still instabilities in the middle of the snowpack in the form of near surface facets and surface hoar buried during the Christmas storm. And of course the snowpack’s basal weak layers still provided cause for concern of deeper instabilities especially near and above tree line on steep, rocky faces and bowls. Several large avalanches ran naturally on basal weak layers over this time.

12/27/16 – Slab avalanche on Schuylkill Ridge that failed on a mid pack instability.

12/26/16 – Natural, 3-5 foot deep, D2.5 persistent slab avalanche in the Anthracites that ran on or near the ground.

With clear skies, cold temperatures and strong solar radiation, future persistent weak layers formed at the snow surface during the dry spell at the end of the year. On southerly aspects, stout melt freeze crusts formed, while northerly aspects experienced near surface faceting.