Center for Snow and Avalanche Studies - CSAS

CODOS Water Year 2013 Updates  >  Grizzly Peak

Water Year 2013 CODOS Summary
for Grizzly Peak

Summary | Snowpack | Melt Rate | Stream Flows


Water Year 2013 entered late winter with dismal snowpack development at ten of eleven CODOS dust-on-snow monitoring sites, Willow Creek Pass being the single exception.  Through March 2013, snowpack SWE totals at all other sites resembled or even fell short of the very dry winter of WY 2012, raising concerns about back-to-back drought seasons.  That broadly consistent spatial pattern in scant precipitation began to diverge in April, 2013.  CODOS sites in the northern Front Range and Colorado River headwaters benefitted most from a series of April and May winter storms that augmented snowpacks and eventually resulted in average or even above average peak SWE levels on average or later-than-average dates.  In the southwestern mountains, fewer and/or smaller April/May storms failed to offset the dry beginning to WY2013 winter.  CODOS sites in the San Juan Mountains experienced, for the second year, substantially sub-par peak SWE values, on near-average dates.  In between, the Central Mountains, Grand Mesa, Park, and northern Gore ranges came closer to but still fell short of average snowpacks. Grizzly Peak was among those sites where WY 2013 snowpack development and peak SWE lagged WY 2012 into March but then surged in late winter and spring to eventually reach near-average levels.

At the CSAS Senator Beck Basin Study Area at Red Mountain Pass, the primary CODOS monitoring site, WY2013 produced a total of ten separate dust-on-snow events, a lower total count than in the past three seasons.  However, the actual mass of dust deposited at Senator Beck Basin in WY 2013 was greater than in any prior season, including the “Martian Winter” of WY 2009.   Dust season began at Senator Beck Basin in November with a single event, February and March delivered four additional events, but the vast majority of dust deposition occurred during events D6 on April 8th and the long-duration D8 event of April 15-17.   As of late March, dust layers observed at Senator Beck Basin were either weak or not present at CODOS sites farther north and east, creating some hope that WY 2013 might be dust-free in parts of the state.  Then, dust events D6 and D8 spelled the end to that possibility with significant depositions statewide near the top of the snowpack.

As at all CODOS sites, dust layers D6 and D8 played the principal role in very significantly reducing snowcover albedo in the Grizzly Peak and Loveland Pass locale as they became exposed, merged, and remained exposed.   Snowmelt rates at the Grizzly Peak Snotel site were sometimes high but frequent periods of reduced solar insolation because of cloud cover, and/or higher albedo after fresh snowfalls, disrupted the potential for maximum radiative forcing of snowmelt in those layers.  Those periods of unsettled weather also interrupted snowmelt runoff. Nevertheless, the Snake River still sustained and exceeded median levels before a final surge to and above median peak flow, close to the median date.

SnowPack & Dust Discussion

SWE accumulation and ablation for Water Years 2012 and 2013, with dust-on-snow events shown as brown bars, by date (as observed at the Senator Beck Basin Study Area).  The long-duration D8 event of April 15-17, 2013, is shown as a heavier bar.  Note that not all dust layers observed at Senator Beck Basin were also found at other CODOS sites.

Snowpack formation at the Grizzly Peak CODOS site and nearby Grizzly Peak Snotel began early but soon stalled, falling into the lower quartile of observed SWE values at that site by November 1 and far behind WY 2012.   A period of stormy weather and SWE gains in December (CSAS Storms #4-8) still placed SWE just behind WY 2012, but early- and mid-January saw almost no further gains.  Snow accumulations finally resumed in late January (CSAS Storms # 10, 11, 12) and proceeded during February and early March at a near-median rate.  Despite having logged four dust-on-snow events at Senator Beck Basin by March 18, the March 19, 2013 snow profile at the Grizzly Peak CODOS site found no discernible dust layers at that location, raising hopes that WY 2013 might be dust-free in the Front Range.   That snow profile found substantial cold content remaining in the snowpack, at a mean snow temperature of -4.1° C.  By late March WY 2013 SWE values at the adjoining Grizzly Peak Snotel finally matched WY 2012 and then continued to build into April.

Then, on April 8/9 a storm (CSAS Storm #19) delivered both fresh snow as well as dust event D6, clearly present in the April 13 snow profile (perhaps merged with layer D5).  That profile presented a still-cold snowcover, at a mean temperature of -1.8° C.  Also observed was evidence of a recent snowmelt episode in and below the former snowpack surface containing dust layer D6/D5 (since buried in new snow). 

A winter storm on April 14/15 (CSAS Storm #20) delivered substantial additional snow as well as the long-duration D8 dust event.  Another brief period of snowmelt followed in late April at the open and sunny Grizzly Peak CODOS snowpit site, with dust layer D8 merging with D6.  Percolating melt water rapidly warmed the underlying snowcover.  Additional spring snowfalls followed in in late April, deeply burying the merged dust layer D8/D6 and insulating the warmed snowpack.  

Peak SWE at the Grizzly Peak Snotel followed on April 24 at 18.4”, 6.5” higher than the WY 2012 peak and 1.3” above the median peak SWE value of 17.1”. Peak SWE for WY 2013 was twelve days later than the median date of Peak SWE (April 12) and over a month later than peak SWE in WY 2012.  A brief period of snowmelt quickly followed peak SWE at the Snotel site, but precipitation resumed until a second, but lower ‘peak’ in mid-May.   Following that second (lower) peak, snowpack ablation was much more rapid than in WY 2012 and the Grizzly Peak Snotel recorded “snow all gone” (SAG) on June 7, 2013, over a month later than in WY 2012.  See the melt rate discussion below.

The site visit on May 10 found 13” of cool new snow over dust layer D8/D6 and an otherwise isothermal snowpack.   Merged D8/D6 had clearly been exposed prior to the recent storm and forced rapid surface melt, thoroughly wetting the entire snowpack to “very wet” condition.   Virtually no exposed dust was visible anywhere in the Grizzly Peak or Loveland Pass locales at that time. 

A final site visit on May 21 again found clean, albeit slushy new snow over the merged D8/D6 layer, and a largely clean snowpack surface in the Loveland Pass locale.  Here and there, though, patches of D8/D6 were emerging in the alpine terrain, previewing what would be a large-scale transformation from high to very low snow albedo.  A concentrated sample of the merged D8/6/5 dust was collected for chemical and other analyses by USGS.

March 19, 2013 snow profile at Grizzly Peak CODOS site:


The March 19, 2013 snow profile at the Grizzly Peak CODOS site.  No dust was discernible in this snowpack, raising hopes
that this could be a dust-free season at this Front Range site.  Snow temperatures were cold, at a mean of -4.1° C.


April 13, 2013 snow profile at Grizzly Peak CODOS site:


On April 13 dust layer D6 was strongly present, buried 3” below the surface and dashing hopes for a clean WY 2013 snowpack. 
D6 may have been merged with event D5.  Clear evidence of a surface melt episode was observed in the snow immediately
below D6 and snow temperatures had warmed from a mean of -4.1° C on March 19 to a mean of -1.8° C.


May 10, 2013 snow profile at Grizzly Peak CODOS site:


Snowpack accumulation was still ongoing in early May.  The CODOS snow profile of May 10 found merged dust layers D8/D6/D5 still
deeply buried under recent clean (and still cold) new snow.  However, recent surface melt associated with late April exposure
of layer D8/D6 had helped produce an isothermal snowpack below those merged dust layers.


During the final visit to Grizzly Peak on May 21, 2013 a concentrated sample of merged layers D8-D6/5 dust was collected near the CODOS site for chemical and other analyses by USGS. 

Melt Rate

As was the case at Senator Beck Basin, layers D8 and D6 were the dominant dust-in-snow features driving snowmelt in the Grizzly Peak locale, although their effects on snowmelt occurred much later in the spring in the Front Range.  Although those layers were deposited in the upper snow column, with brief periods of sustained exposure under clear, sunny skies, cloud cover sometimes reduced solar insolation and/or minor amounts of fresh snow temporarily restored a higher albedo to the snowpack, marginally slowing melt rates.  Overall, the snowmelt cycle was somewhat later than median timing.

Grizzly Peak Snotel Melt Rate Summary Table
Analysis of Grizzly Peak Snotel data for Water Years 2006-2013 snowmelt seasons showing date and quantity of peak SWE, days from peak SWE to “snow all gone” (SAG), total additional precipitation after the date of peak SWE, an “adjusted” mean daily rate of snowmelt adding the additional precipitation to the peak SWE total, the maximum five-day moving average of daily melt, and the mean air temperature over the entire snowmelt period, from peak SWE to SAG.  The Grizzly Peak Snotel site is substantially shaded by surrounding forest.

Following peak SWE at the Grizzly Peak Snotel of 18.4” on April 24, 2013, an additional 4.9” of SWE was added to the snowpack during the ablation cycle for an adjusted total of 23.3” of SWE available to melt.  Even under slightly warmer mean air temperatures than in spring 2012, WY 2013 snowpack ablation to SAG took 44 days to melt 8.8” more SWE than was available in WY 2012, also melted over 44 days.  Spring 2013 melt rates were as high as 1.7” SWE loss per day.  However, given the frequent disruptions to maximum potential radiative forcing caused by the unsettled weather after peak SWE, the mean daily SWE loss over the entire snowmelt period was just 0.53” per day, near the mean of mean daily melt rates observed at the site during the period of analysis but still higher than the 0.33” mean daily melt rate of spring 2012. The maximum 5-day moving average daily melt rate was 1.14” SWE loss per day. SAG occurred on June 7, about a week later than the median date of SAG at Grizzly Peak.

Grizzly Peak Pagano Plot
WY 2013 SWE accumulation and ablation at the Grizzly Peak Snotel station, with upper and lower quartiles of period of record shown in light grey, middle quartiles in dark grey, and the median trace for the period of record shown as a dashed line. Note that whereas this plot records peak SWE above the period of record median peak, the other Grizzly Peak SWE plot shows WY 2013 peak SWE at the 1971-2000 mean peak.

Stream FlowS

Comparison of WY 2011, 2012 and 2013 (in progress) hydrographs for the Snake River Near Montezuma gauge highlights variations in snowmelt runoff timing and volume over those three seasons.  WY 2011 snowmelt runoff in the Snake River watershed began early and oscillated as dust-in-snow was alternately exposed and reburied under relentless spring storms. Eventually, flows surged strongly to a far above-average peak near the average date of peak discharge, as dust finally emerged and remained exposed.  Flows then remained high for an extended period, well above median values on the descending limb, and remained well above median levels throughout the summer.  

WY 2012 snowmelt runoff also began early, before the gauge came on line, when flows were already surging to above median levels.  However, the very poor snowcover was quickly consumed and early peak flows fell well short of median values and then quickly declined at the end of snowmelt runoff.  WY 2012 total snowmelt runoff yields were very far short of average yields. 

This season, thanks to stormy March and April weather, onset of snowmelt runoff in the Snake River watershed was slightly delayed past median timing.  Once underway, flows at the gauge quickly reached median levels.  As of this writing (June 17, 2013), the Snake River has surged to an above-average peak, with near-average timing, and has begun its descending limb. With summer solstice approaching, sustained radiative forcing of snowmelt in the merged D8/D6 dust is likely to maintain very high melt rates in the remaining snowcover in the Grizzly Peak and Snake River watershed locales until all snowcover is ablated.  As a result, WY 2013 may produce a steeper-than-normal descending limb on the Snake River Near Montezuma gauge hydrograph.