By Arden Feldman            CBAC Intern

The major dome of high pressure over the western US continued to bring calm, sunny weather and record high temperatures to the Crested Butte area for another week. The Elkton weather station at 11,000 ft recorded daytime highs in the mid to upper 40s from March 15^th through the 21^st, and nighttime lows that did not drop below freezing from the 14^th through the 20^th. It was full blown “beach weather” for Crested Butte’s spring break. On the 21^st a moisture-laden Pacific trough began digging towards the California/Baja coast. This initially brought a warm, moist southwest flow with a mix of sun and clouds through the 22^nd. On the 23^rd, the high pressure and above average temperatures were finally pushed out by the trough and a closed low pressure system began impacting Colorado with a cold front. The storm hammered the San Juan Mountains but came in relatively light for our area with Irwin and CBMR reporting 2-4 inches on the 24^th, Schofield Pass recording 9 inches, and unusually tame NW winds gusting into the 40s. Skies cleared by the morning of the 25^th allowing for fantastic weather for the Grand Traverse. A weak, fast moving trough brought light snow showers to the area that night. The storm quickly moved past and skies cleared again, with generally cooler temperatures on the 26^th and 27^th. Overnight lows were back down to the low 20s. Spring squalls due to a closed low moving overhead brought 3-4 inches of snow on the night of the 27^th into the morning of the 28^th. The 29^th and 30^th were another set of warm and calm days before a final closed low pressure system on the 31^st. This storm came in light and warm with general accumulations of 1-2 inches and 6 inches at Schofield Pass.

3/20/17 – Satellite image showing the moist Pacific trough beginning to impact the west coast.

On March 16^th the persistent slab problem was finally removed from the list. The last human triggered persistent slab avalanche on the buried near surface facets occurred on March 4^th, suggesting the layer had become dormant or unreactive in its dry snow state. However, the string of increasingly warm days without solid overnight freezes introduced more and more free water into the snowpack, especially on east, south, and west aspects, and persistent slab concerns were replaced with wet slab concerns. This free water was getting deep enough in the snowpack to pool up on these buried crusts and weak layers, potentially destabilizing them and threatening to release wet slab avalanches. Wet slab avalanches remained on the problem list until the 23^rd when colder temperatures aided in refreezing the snowpack.

3/18/17 – Natural wet slab/glide crack avalanche on an east aspect at 10,500ft.

The continued warm weather with poor refreezes was also causing an increase in frequency and potential size of wet loose avalanches. The large amount of free water in the snowpack was creating the potential for small point releases to gouge down and become bigger and far more consequential. On the 22^nd, this threat, along with wet slab concerns, raised the avalanche danger to Considerable below tree line. Large wet loose avalanches posed a threat until the 24^th when new snow and a solid freeze limited the wet loose avalanche concerns to small surface instabilities through the 25th. Loose wet avalanches then stayed off the problem list until the 29^th and 30^th, when warmer temperatures and some new snow brought back the potential for small wet loose avalanches involving the fresh snow.

3/16/17 – Large natural wet loose avalanche on Gibson Ridge.

3/19/17 – Large natural wet avalanche below Gothic Peak that gouged down and triggered wet slab avalanches on its flanks.

The 2-9 inches of new snow combined with moderate NW winds on the 23^rd, added small wind slabs to the problem list until the 25^th. The spring snow squalls on the night of the 27^th again added small wind slabs to the problem list on the 28th. In both cases the wind slabs were confined to loaded, above tree line slopes. On the 26^th, 27^th, and 31^st, solid overnight freezes and little to no fresh snow resulted in no avalanche problems and the avalanche danger being rated at Low at all elevations.

By Arden Feldman            CBAC Intern

With a broad ridge of high pressure shifting east over the continental US, March 3^rd and 4^th were quite pleasant with sunny skies, light winds, and daytime high temperatures just above freezing. The next Pacific trough of low pressure began coming ashore on the 5^th, briefly bringing back stormy weather. An associated cold front on the morning of the 6^th brought 4 to 7 inches of new snow and cold temperatures, but the big story was the extreme westerly winds mixing down to all elevations caused by a relatively low elevation jet and a strong pressure gradient. On the morning of the 6^th, winds were blowing at 60 mph and gusting to 100 mph on Scarp Ridge. On the 7^th the storm track shifted northward as a high pressure began to build over the West. The high pressure lasted through the rest of the work week and brought a warming trend, calm winds and sunny skies. On the 10^th, Elkton reached a high temperature of 43 degrees Fahrenheit. A pair of fast moving disturbances brought back unsettled weather on the 11^th and 12^th. These shortwave troughs resulted in some snow further north, but only brought increased clouds and gusty winds around the Crested Butte Area. High pressure took hold over the West again on the 13^th allowing for calm and dry weather and temperatures approaching near record highs through the 15^th.

3/9/17 – Satellite image showing the first disturbance heading for Colorado.

3/13/17 – Satellite image showing the second disturbance fleeing to the east.

Persistent slabs 1 to 3 feet thick over facets and facet crust combos buried mid February remained an avalanche problem through the first half of March on north through southeast aspects. These slabs remained sensitive to triggers through the first week of March. The problem slowly stabilized, and the danger dropped from Considerable on March 3^rd to Moderate on the 4^th and 5^th. The extreme wind event on the 6^th added weight to the slabs and raised the danger back to Considerable for the day. Eventually, after more time to stabilize and a lull in avalanche activity, the danger dropped down to Low at all elevation bands on the 13^th.

3/2/17 – Skier triggered persistent slab avalanche on a NE aspect NTL on a very thin, faceted crust.

3/2/17 – Persistent slab avalanches in Evan’s Basin.

3/2/17 – Natural D2 slab avalanche on an ENE aspect ATL.

March 3^rd and 4^th brought the first above freezing temperatures since the new snow on February 28^th, adding loose wet avalanches to the problem list. These avalanches were small but concerning due to the potential for them to subsequently trigger larger persistent slab avalanches. Loose wet avalanches came back to the problem list on the 14^th and 15^th due to the near record high temperatures. They remained relatively small, but still potentially consequential.

3/14/17 – Wet slab/mud slide near Kebler Pass Road.

The extreme westerly wind event on the 6^th added wind slabs to the problem list through the 8^th. The wind event seemed to do more wind scouring than loading, but some spots still harbored small but dense wind slabs that would make for unpleasant surprises, especially in consequential terrain.

By Arden Feldman            CBAC Intern

After the cold front on February 23^rd, the Crested Butte area was stuck in cold, northwest flow until the 26^th. Embedded disturbances within the flow kept clouds and convective snow showers overhead during this period but did not result in significant accumulations. Temperatures were cold with a high at Elkton of 6 degrees Fahrenheit on the 24^th, reminding ourselves how soft we’ve gotten during this unusually warm winter. Ahead of an incoming storm, southwesterly flow increased on the 26^th resulting in gusty winds. The combination of a cold front, the jet stream bringing in subtropical moisture, and an upper level low pressure trough further adding instability, resulted in a powerful winter storm on the 27^th and 28^th. By the evening of the 28^th, 8 to 25 inches of snow fell across the forecast area. Schofield Pass picked up 25” of snow (2.4” SWE) while Kebler Pass received 18” of snow (1.5” SWE). For the rest of the week, the Crested Butte area remained in dry, cold, northwest flow allowing for light winds, sunny skies, and cold temperatures.

2/27/17 – Satellite image showing the major storm system impacting Colorado.

Wind slabs from strong winds the week prior and continued winds this week remained the primary avalanche problem through the first half of the week. On February 25^th, the persistent slab problem from the surface hoar layer buried January 19^th was finally put to rest and taken off the problem list. This was after over two weeks without a persistent slab avalanche being reported in our forecast area, and 11 days since one was reported in the Aspen Zone. We were allowed two days without a persistent slab problem until a new persistent weak layer became active during the powerful storm on the 27^th. A layer of near surface facets that formed during the previous dry weather was now being put to the test. On the 28^th the avalanche danger was raised to Considerable at all elevations and we were dealing with a significant natural slab avalanche cycle. These slabs were primarily failing on fragile facet and crust-facet layers 1-3 feet deep, most commonly on easterly facing wind-loaded aspects above treeline. The storm also brought about wind and storm slabs that were quick to heal and off the problem list by March 2^nd.

3/1/17 – Large persistent slab avalanche on a SE aspect ATL.

3/1/17 – Multiple slab avalanches on E aspects ATL.

3/1/17 – Natural D2 slab avalanche on a NE aspect.

2/26/17 – Snow pit showing an example of the concerning crust facet sandwich in our snowpack.

2/23/17 – Small wind slab on a SE aspect NTL.

By Arden Feldman CBAC Intern

The week began clear and warm on February 17^th but high clouds began to build on the 18^th from a deep Pacific trough making landfall on the California coast. Moisture associated with the trough began streaming in from the southwest on the 18^th but unfortunately the bulk of the energy and precipitation remained out near the west coast. Accumulations were only marginal with occasional light snow showers into the 19^th. On the afternoon of the 19^th a low pressure trough moved over Colorado, bringing with it a warm, moist air mass with southerly flow. This system brought snowfall through the night and resulted in 2 to 8 inches of snow across our area by the morning of the 20^th, favoring the Kebler Pass and Paradise Divide zones. Strong westerly winds accompanied the new snow.

A temporary ridge built overhead on the 20^th allowing for scattered skies and warm temperatures. Another Pacific trough began to move onshore on the 21st, quickly breaking down the ridge. Associated moist southwest flow stayed to our north and west in Wyoming and Utah. Being on the edge of this flow we saw increasing clouds and strong winds on the 21^st and 22^nd. The Elkton weather station recorded a 102 mph gust on the 21^st. Finally on the morning of the 23^rd a cold front drifted south over the Elk Mountains and brought steady snowfall with it. 8 to 10 inches of snow, driven by strong west to northwest winds, accumulated on the 23^rd. The Schofield Pass Snotel Site recorded .5” of SWE and 10” of snow.

2/20/17 – Satellite image showing the break between storms on February 20th and the approaching system that would bring 100+ mph wind gusts and a quick blast of snow.

Persistent slabs on buried surface hoar 1 to 3 feet deep were the avalanche problem in the beginning of the week. The slabs were becoming increasingly unreactive but were still possible to trigger on near tree line northerly slopes. By the end of the week they had become unlikely to trigger. No new persistent slabs were observed this week and the last reported persistent slab occurred on February 14^th in the Aspen Zone.

2/20/17 – Snow pit showing a 3 foot slab over propagating surface hoar on a NE aspect near tree line.

The new snow and strong westerly winds on the afternoon of the 19^th built wind slabs on leeward aspects near and above tree line, and wind slabs were added to the problem list on the 20^th. With continued strong winds and more snow on the 23^rd, the wind slabs stuck around through the end of the week and kept the avalanche danger rating at moderate near and above tree line. They remained possible to trigger and small to large in size. During the second half of the week, several wind slabs were skier triggered and were responsible for a couple of close calls (Coon Basin, Purple Peak). ­­

2/20/17 – Remotely triggered wind slab that ran 1,500 feet.

2/21/17 – Crown of a large wind slab avalanche that caught, partially buried, and injured a skier.

2/20/17 – Skier triggered wind slab on an east aspect at Irwin.