Water Year 2013 CODOS Summary for
Hoosier Pass
Summary | Snowpack | Melt Rate | Stream Flows
Summary
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. The Hoosier Pass Snotel was among those sites where WY 2013 snowpack development and peak SWE surged in late winter and spring and eventually reached 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 Hoosier Pass locale as they became exposed, merged, and remained exposed. Melt rates at the Hoosier Pass Snotel site were comparatively high despite periods of unsettled weather and fresh snowfalls, disrupting the potential radiative forcing of snowmelt. Those periods of reduced solar insolation because of cloud cover, and/or higher albedo after fresh snowfalls, occasionally interrupted surging but the Blue River 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 Hoosier Pass CODOS site and nearby Hoosier Pass Snotel began very poorly, quickly falling well behind WY 2012 then below the historic range of SWE values for the site. A period of stormy weather and SWE gains in December (CSAS Storms #4-8) still placed SWE at historic lows and early- and mid-January saw almost no further gains. Snow accumulations finally resumed in late January (CSAS Storms # 10, 11, 12) and SWE accumulation proceeded during February and early March at a higher-than-median rate. By late March WY 2013 SWE values matched WY 2012. Despite having logged four dust-on-snow events at Senator Beck Basin by March 18, the March 18, 2013 snow profile at the Hoosier Pass CODOS site found no discernible dust layers at that location, raising hopes that (at least) WY 2013 might be dust-free at this site. That snow profile found some cold content remaining in the snowpack, at a mean snow temperature of -3.8° C.
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 -3.6° C. Also observed was clear 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 additional snow as well as the long-duration D8 dust event. Another period of snowmelt followed in late April at the open and sunny Hoosier Pass CODOS site, with dust layer D8 briefly exposed and percolating melt water rapidly warming the underlying snowcover. Additional spring snowfalls followed in early May, deeply burying dust layer D8 and insulating the warmed snowpack.
The May 9 site visit found a completely isothermal snowpack. Some 15” of recent, clean new snow covered the very heavy D8 layer and layer D6 was separated from D8 by another 10” of clean snow. Virtually no exposed dust was visible anywhere in the Hoosier Pass or Ten Mile Range locales at that time. Merged D8/D6 had clearly been exposed prior to that recent storm and forced rapid surface melt, thoroughly wetting the entire snowpack to “very wet” condition.
Peak SWE at the Hoosier Snotel followed on May 11 at 16.8”, 6.6” higher than the WY 2012 peak and 0.8” above the median peak SWE value of 16.0”. Peak SWE WY 2013 was sixteen days later than the median date of Peak SWE (April 25) and almost six weeks later than peak SWE in WY 2012. Dry weather and rapid snowmelt quickly followed peak SWE at the Snotel site, eventually enhanced by the emergence of dust layer D8 and the merging of layer D8 with layer D6. Overall, the rate of snowpack ablation was much more rapid than previously observed. However, given the very early snowmelt cycle of WY 2012, the Hoosier Snotel recorded “snow all gone” (SAG) on June 7, 2013, 23 days later than in WY 2012. See the melt rate discussion below.
The March 18, 2013 snow profile at the Hoosier Pass 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 -3.8° C.
On April 13 dust layer D6 was strongly present, buried 3” below the surface and dashing hopes for a clean WY 2013 snowpack. Clear evidence of a
surface melt
episode was observed in the snow immediately below D6 but snow temperatures had warmed only slightly, from a mean of -3.8° C on March 18 to a mean of -3.6° C.
Snowpack accumulation was still ongoing in early May. The CODOS snow profile of May 9 found dust layer D8 still deeply buried under recent clean snow.
Layer
D8
had not yet merged with dust layer D6. However, recent surface melt associated with late April exposure of layer D8 had helped produce an isothermal snowpack.
During the final visit to Hoosier Pass on May 22, 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 Hoosier Pass locale, although their sustained effects occurred much later in the spring. 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 and marginally slowed melt rates. Overall, the snowmelt cycle was somewhat later than median timing.
Analysis of Hoosier Pass 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 Hoosier Pass Snotel site is heavily shaded by surrounding forest.
Following peak SWE at the Hoosier Pass Snotel of 16.8” on May 11, 2013, an additional 0.6” of SWE was added to the snowpack during the ablation cycle for an adjusted total of 17.4” of SWE available to melt. Delayed by spring storms, and aided by the intensity of radiative forcing in dust layers D8 and D6, and under warmer mean air temperatures than in spring 2012, when most snowmelt occurred in March, WY 2013 snowpack ablation to SAG took only 27 days. Spring 2013 melt rates were as high as 1.6” SWE loss per day. The mean daily SWE loss over the entire snowmelt period was 0.64” per day, the highest mean daily melt rate observed at the site in the period of analysis and much higher than the 0.27” mean daily melt rate of spring 2012, when it required 21 more days to fully ablate 4.3” less available SWE.
Given the minimal precipitation following peak SWE, the interruptions in radiative forcing described above were perhaps somewhat less frequent at the Hoosier Pass site than at other CODOS sites where peak SWE occurred earlier in the season. Despite that, the maximum 5-day moving average daily melt rate was 1.16” SWE loss per day, a lower rate than observed in WYs 2010 and 2011. SAG occurred on June 7, about a week later than the median date of SAG at Hoosier Pass.
WY 2013 SWE accumulation and ablation at the Hoosier Pass 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.
Stream Flows
Comparison of WY 2011, 2012 and 2013 (in progress) hydrographs for the Blue River Near Dillon gauges highlights variations in snowmelt runoff timing and volume over those three seasons. WY 2011 snowmelt runoff in the Blue River watershed began early and oscillated as dust-in-snow was alternately exposed and reburied under relentless spring storms. Eventually, flows surged sharply to an 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 a normally descending limb, and remained well above median levels throughout the summer.
WY 2012 snowmelt runoff also began early, before the gauge came on line, already surging to above-median flows. 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 Blue River watershed began perhaps a month later than in WY 2012. Once underway, flows at the gauge quickly reached median levels, even with above average diversion flows upstream at the Hoosier Pass Tunnel. As of this writing (June 17, 2013), the Blue 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 Hoosier Pass, Mosquito Range, and Ten Mile Range locales until all snowcover is ablated. As a result the WY 2013 hydrograph may depict an unusually steep descending limb.
On the South Park side of the Continental Divide, hydrographs for WY 2011, 2012, and 2013 at the USGS Tarryall Creek At Upper Station Near Como gauge present patterns in snowmelt runoff that very closely mirror those on the Blue River. To-date, spring 2013 runoff behavior in Tarryall Creek is as described for Blue River.