Summary

Senator Beck Basin and the Red Mountain Pass locale have received five dust-on-snow events to-date, two of which produced substantial deposition (events D3 and D4, on March 26 and March 30 respectively) and the last of which (D5) was inconsequentially weak. In our most recent snow profile at the Swamp Angel Study Plot on Friday, March 28, 2014 we measured 25.3” (642 mm) of SWE in our snow profile.  That site visit revealed event D3-WY2014 buried 11” below the surface in the new snow that arrived with event D3. 

Senator Beck Basin and the Swamp Angel Study Plot (SASP) are in headwaters of the Uncompahgre River.  Snotel summary data for our two major watersheds as of today, April 4, report percentages of near-median Peak SWE in the Gunnison Basin (at 103%) and significantly below median Peak SWE in the San Miguel, Dolores, Animas and San Juan River Basins (at 82%).  

Some cold content remained in the snowpack in our March 28 snow profile at SASP and the snowpack was ‘dry’ throughout.  On March 30 dust event D4-WY2014 was deposited, virtually ‘dry’, onto the Senator Beck Basin snowpack with minimal accompanying snowfall thinly covering the new dust.  D4 became extensively emerged in the subsequent days until an additional 6” of snow fell over the past 48 hours, re-burying D4.   As of this writing, both the Uncompahgre River Near Ridgway gauge and the Animas River At Durango gauge are reporting flows below median levels at the beginning of the ascending limbs in those hydrographs.  Although additional small amounts of snow are likely in the coming several days, dust layer D4 may emerge in the coming week, absorbing solar radiation and accelerating the warming of the underlying snowcover at higher elevations, or enhancing snowmelt rates at lower elevations where the snowcover was already isothermal.  Under current conditions, and with average spring weather, spring 2014 hydrographs in western San Juan Mountain watersheds could follow a pattern within the range between the WY 2009 and WY2013 hydrographs.  However, given recent history, additional dust-on-snow deposition is likely.

Snowpack & Snow Profiles

Despite reporting consistently well-below-average SWE statistics for the greater San Miguel, Dolores, Animas and San Juan River Basins Snotel network, the Red Mountain Pass Snotel (and Senator Beck Basin locale) generally hovered near normal daily SWE values throughout much of the winter, benefiting more from storms from the NW than other locations farther south and/or east in those watersheds.  Similarly, portions of the Gunnison River Basin also prospered from N’ly flow and storms, many of which tracked just north of the San Juan Mountains.  As of today, April 4, the Gunnison River Basin, of which the Uncompahgre River is a tributary, is reporting 103% of median SWE.  On the south side the Red Mountain Pass, the combined San Miguel, Dolores, Animas and San Juan River Basins Snotel network is reporting only 82% of median Peak SWE.  , within the range of median dates of Peak SWE in those basins.  In both basins, individual Snotel sites are approaching or are already within the range of dates of Peak SWE.

As of this morning, the Red Mountain Pass Snotel just 2 km to the south of Swamp Angel Study Plot, in the Animas River watershed, is reporting 93% of median Peak SWE, at 23.0”; the median date of Peak SWE at that site is April 26.  Southwest of Senator Beck Basin and Red Mountain Pass, in the headwaters of the Dolores River, the Lizard Head Pass Snotel is reporting 94% of median Peak SWE, at 15.4”; median peak SWE date is April 6 at that site.  Both sites were at/near 100% levels not long ago.

March 28, 2014. Dust layer D3 is very apparent above, as we prepared to collect a 0.5 m2 sample of the dust layer for mass and chemical analysis by our USGS partners.

Snowmelt and Stream Flow

Given the still-cool snow temperatures even at the lowest point in Senator Beck Basin (Swamp Angel Study Plot), no significant snowmelt discharge has been released from our snowpack to-date.  Senator Beck Stream Gauge (SBSG) operations resumed on March 18, capturing over-winter base flows very similar to the flows recorded when the instruments were finally removed on December 27, to prevent ice damage during the cold months.  Current flows remain effectively at that base flow level.  Note that the median flow curve shown for SBSG is based on a short period of record, beginning in WY 2006, and that dust-on-snow has significantly influenced runoff behaviors throughout that period.

As of this writing, on April 4, both the Uncompahgre River Near Ridgway gauge and the Animas River At Durango gauge are reporting flows just below median levels, at the beginning of the ascending limbs in those hydrographs.  Farther west, the Dolores River at Dolores gauge is farther advanced on the median ascending limb, showing only minor fluctuations from the median curve.  Snowmelt has been contributing to those increasing Dolores River flows since at least early March, from the lower elevation and isothermal snowcover in that SW’ly oriented watershed.  Dust event D2 was notably heavier in that watershed than we observed in the Silverton area, so D2 and eventually D3 both likely enhanced this initial snowmelt.  Headwater snowpacks there still retain some cold content, like our own Senator Beck Basin snowpack in the headwaters of the Uncompahgre and adjacent to headwaters of the Animas and San Miguel rivers, near Red Mountain Pass.

Wind

Windroses for all five dust-on-snow events of Water Year 2014 are shown above.  As discussed in our March 17 Update, winds during the October 1, 2013 through March 17, 2014 show a notable bias toward the W-to-N quadrant as seen in the windrose below (left), with an average direction of 291° (WNW).  That high proportion of winds from the W-to-N sector  limited opportunities for SW or W winds to deliver much dust to Senator Beck Basin from the Colorado Plateau source areas in southern Utah and farther south, although event D2 was from the WNW (mean direction 292°).  Since then, we have seen a substantial increase in the proportion of SW and S winds, as seen in the windrose below (right), with a mean direction since March 17 of 255° (WSW), and the strongest winds from the SSW at up to 75 mph (during D4).  That shift in the regional wind field, created by more active weather in the Great Basin (versus the persistent high pressure of the mid-winter), has enabled the recent potent dust events D3 and D4.  Winds associated with D4 were strong enough to deliver muddy rain as far east as Colorado Springs and perhaps to other Front Range cities.

At present, snowpack conditions at Senator Beck Basin and in the Red Mountain Pass locale could be placed in the “Average Peak SWE” domain in the table above. Dust conditions could be described as “Moderate”, perhaps verging toward “Heavy” – the full exposure of D4 and its merger with D3 may tip the scale into the “Heavy” range, even absent additional dust events.  Samples of D3 and D4 are now being processed for mass content by our USGS partners.

As always, spring weather will dictate the frequency and duration of dust exposure at the snowpack surface and the consequent impacts of reduced snow albedo on snowmelt runoff timing and rates.  As of this writing (Friday, April 3) Senator Beck Basin and the western San Juan Mountains have received several inches of new snow over the past 48 hours and additional accumulations are expected over the coming weekend, burying dust layer D4 even further with clean snow.  A high pressure ridge and drier weather is expected to develop by mid-week next week (April 8 or 9).   

Given those near-term forecasts, and the depth of clean snow above layer D4, high snowcover albedo will persist and delay dust enhancement of Senator Beck Basin (SBB) snowpack warming and the onset of lower snowmelt runoff from S’ly aspects in lower SBB well into next week, if not longer.  Should the mid-range weather forecast be correct, the expected dry period in the 6-10 day outlook may ablate as much as 1" of clean SWE currently above layer D4 and enable D4's exposure at progressively higher elevations over time, perhaps even merger with layer D3.  Prolonged exposure of layer D4/D3 would accelerate snowpack warming on the higher and cooler aspects of SBB terrain, where cold content remains, and perhaps bring the snowcover on solar aspects in the lower elevation SBB snowcover to a fully isothermal state (at 0.0° C throughout), finally initiating the onset of snowmelt runoff.   

In the longer term, given current dust conditions combined with near-average Peak SWE, average spring precipitation in April and May, and the absence of runoff to-date,  the Senator Beck Stream Gauge hydrograph could resemble WY2009 on the ascending limb, with numerous but erratic surges in discharge to above average peak levels followed by a rapid decline in flows (the second surge in the WY 2009 was the result of very heavy rain and rain-on-snow in late June).   Should the remainder of April and May be drier than average, the Senator Beck Stream Gauge (SBSG) hydrograph would be further amplified and compressed, with even more rapid surges to an even higher peak followed by a more rapid decline to low flow levels. 

Since Senator Beck Basin is a headwater catchment in the Uncompahgre River watershed, average spring weather may result in a hydrograph at the Ridgway gauge that also resembles WY 2009 (without the late-June surge) showing a rapid rise in flows later in April, with additional surges in May to an above-average and early peak followed by a steep decline.

To the south, where the Animas watershed has already experienced significant dust-enhanced snowmelt and lost some of its snowpack, under the influence of a much heavier D2 dust layer, average spring precipitation could also result an Animas River At Durango hydrograph comparable to the WY2009 hydrograph, surging quickly to and experiencing episodes of above average flows throughout the ascending limb to an above-average and early peak, followed by a steep descending limb (without the late-June surge).  Should the remainder of April and May be drier than average, the Animas River hydrograph would be further amplified and compressed, with a more rapid surge to an even earlier peak followed by a more rapid decline to very low flow levels, before or during the period when normal peak flows occur.

To the west, both the Dolores and San Miguel watersheds are already experiencing some minor snowmelt runoff, at the beginning of the median ascending limbs on those hydrographs.  Given average spring weather and below-average snowpack, the Dolores River may see a hydrograph splitting the difference between the WY 2013 and WY 2009 (without the late-June surge) patterns, with erratic and rapid surging to an early, somewhat above average peak flow, followed by a steep descending limb.  If April and May are drier than normal, the runoff cycle would be further compressed, in duration, and ‘flashier’ in amplitude, with a sharp descending limb to very low flows just when normal peak flows would be occurring.

Unfortunately, recent history suggests that further dust-on-snow loading is likely in the western San Juan Mountains and in these watersheds as the remainder of April and May unfold.  Additional dust will add to the mass of dust as layers merge, further reducing snow albedo and increasing the absorption of solar energy, when exposed.

See the Senator Beck Basin CODOS Site Reference Page for site details and an archive of site-specific reports.