Major reductions in snow albedo caused by merged dust layers were readily observed at the snowpack surface, at all elevations and on all aspects, during a recently completed circuit of CODOS sites at Grand Mesa, Hoosier Pass, Loveland Pass (Grizzly Peak), Berthoud Pass, Willow Creek Pass, Rabbit Ears Pass, and McClure Pass, and a special visit to Independence Pass. Snowcover was largely confined to terrain at or above treeline, or in high elevation dark timber, and very high melt rates were rapidly eroding that snow under sunny skies and warm temperatures; some of the Snotels adjoining our CODOS snow profile sites were at or near ‘snow all gone’. As the Memorial Day weekend clean snow layer was ablated just prior to and during this trip, and merged dust layers D3-D8 re-emerged, very high, dust-enhanced snowmelt rates surged and produced runoff flows significantly exceeding median peak levels. At a minimum, streams and rivers in these watersheds were running at bank full and many were producing minor flooding. Since those site visits, most hydrographs continued to climb until, just recently, either plateauing or perhaps beginning the descending limb of the runoff cycle, as the remaining snowpack was being rapidly consumed.
Increasing afternoon cloud buildup can reduce the potential solar energy reaching the alpine snowcover but high, dust-enhanced snowmelt rates will continue as major reductions in snow albedo convert solar energy to snowmelt during daylight and warm overnight air temperatures help sustain snowmelt during darkness.
CODOS Site Conditions
The following images illustrate dust-on-snow and snowcover conditions observed during the field excursion on June 2-4 and show ‘all (dust) layers merged’ (ALM) at the snowpack surface. ALM samples were collected at each CODOS snow profile site except Willow Creek and McClure Passes, which had no snowcover left, and also at Independence Pass. A final snow profile was performed at the Senator Beck Basin Swamp Angel Study Plot on June 5 before that site also lost its snowcover two days later, on the evening of June 6.
Grand Mesa – June 2, 2014
Independence Pass – June 2, 2014
Hoosier Pass and Ten Mile Range – June 3, 2014
Grizzly Peak and Loveland Pass – June 3, 2014
Berthoud Pass – June 3, 2014
Willow Creek Pass and North Park – June 3, 2014
Rabbit Ears Pass – June 3 and 4, 2014
McClure Pass – June 4, 2014
Swamp Angel Study Plot – June 5, 2014
Upper Colorado River Basin Snowpack
As of June 4, the combined Upper Colorado River Basin Snotel network SWE plot showed that snowpack was largely consumed and approaching ‘snow all gone’ at the Snotel sites represented. Most remaining snowcover in the watershed was at higher elevations, in alpine terrain or at treeline. Individual Snotel site conditions vary from the plot shown above and we have posted the most current individual Snotel plots available, as of this writing, at our individual CODOS site web pages. On the east side of the Continental Divide, a large fraction remains of the above-average snowpacks recorded at some headwater Snotels such as Joe Wright, Loveland Basin, and University Camp. Dust-on-snow conditions in those headwaters should be assumed to resemble those observed at the Grizzly Peak and Berthoud Summit Snotel sites.
Even with increased cloud cover (and decreased solar potential), snow albedo is very low throughout the Colorado mountains and, aside from occasional hail or snow showers, will remain so until ‘snow all gone’. Snowmelt rates will, therefore, remain higher than average and the remainder of the snowcover will likely be depleted more quickly, at a higher rate of daily SWE loss, than the median trace representing 1981-2010 snowpack ablation on Snotel plots would indicate. The earliest, “minimum” projection of SWE content and eventual ‘snow all gone’ date may best reflect recent dust-enhanced snowmelt rates in these NRCS projection plots.
As discussed in our May 29 CODOS Alert, snowmelt runoff surging in upper Colorado River watersheds reached very high peak flows in early June, substantially exceeding median peak discharge levels in all watersheds, somewhat earlier than the median average date of peak flow. Although also at a substantially higher level than average, peak flow on the Yampa more closely matched median peak timing. Current hydrographs, as of this writing, are posted at those individual CODOS site webpages.
In all these watersheds, very high, dust-enhanced late-May and early June snowmelt rates were driven by rapidly declining snow albedo, as merged dust-on-snow layers, including layer D8, emerged at all elevations and on all aspects of the remaining snowcover. These very high snowmelt rates and high runoff levels would not have been matched in the absence of dust on the snowcover, given the same weather conditions.
As of this writing, on Monday, June 9, all hydrographs that CODOS normally monitors in those watersheds have now begun reporting declining flows. Several factors including decreasing solar energy inputs caused by increased cloud cover and rapidly decreasing snowcover available for melt could be contributing to those initial declines. Aside from short-lived ‘albedo reset’ episodes caused by fresh hail or snow, current very low snow albedo levels will persist until ‘snow all gone’. Snowmelt rates will remain generally high and the remaining snowpack in these (and all Colorado) watersheds will continue to be depleted at a high rate.
As a result, given normally dry and warm June weather, hydrographs in these and all other Colorado watersheds are unlikely to replicate their median descending limbs. Very high, dust-enhanced snowmelt rates will rapidly consume the declining snowcover. Hydrographs may, as a result, exhibit steeper-than-average descending limbs that initially drop to levels closer to normal peak flows and then, later, to low levels for a given June date, until more normal flows are perhaps restored by monsoonal rains in July and August. Water Year 2006 hydrographs at the Upper Colorado River tributary stations that CODOS monitors provide an example of this steeply descending limb in June following high peak flows – see the hydrograph archives on those specific CODOS site webpages.
Mid-Range Weather Forecast
Generally dry and seasonably warm weather is anticipated to reign over western Colorado for the current week ending June 14, with occasional chances for afternoon showers. NOAA’s Climate Prediction Center outlooks for June 16-22 precipitation and temperatures, issued on June 8, foresee conditions leading up to the summer solstice that could sustain current Colorado snowmelt rates in the snowpack that remains.
WY 2014 Season Summary Reports
Later this summer, after the proverbial dust finally settles, CODOS will prepare and post Water Year 2014 Season Summary reports for each CODOS site, including Senator Beck Basin, appending those reports and updated hydrographs and Snotel data and other analyses to individual CODOS site archival webpages (linked from the top of http://www.codos.org). Once again, we thank our CODOS program funders for your collective support for the Colorado Dust-on-Snow program, and look forward to discussing how the program can continue to support your organizations with useful applied science and information.