Summary
The majority of the April CODOS tour was accomplished just prior to a significant closed low pressure system that set up over the four corners region and deposited at least 1” of precipitation at most CODOS sites across the state from April 15-17. We postponed visiting Grizzly Peak (Loveland Pass) and Berthoud Pass until the storm subsided and allowed safe travel (mainly from other motorists) to these sites.
Both Berthoud and Loveland Pass, as of April 22, were dust free. On April 14, Willow Creek and Rabbit Ears Pass were also dust free. If these four CODOS sample locations have not received dust from D5 – occurring Saturday, April 23 – then they remain the only CODOS locations in the state, to date, that will not have snowmelt impacted by dust.
Berthoud Pass – April 22
As mentioned above, Berthoud Pass has remained dust free so far the WY2016 season. The snowpack is isothermal. The CODOS measurement of SWE increased from 20” on March 20 to 26” on April 22 (see plot below). From the April 15-17 storm event, Berthoud Summit SNOTEL received 2” of SWE, 20” of snow accumulation, and 2.5” of precipitation. Currently, Berthoud SNOTEL has exceeded its median Peak SWE by 0.8” (historical Peak SWE of 21.8” on median Peak date April 29) and is currently 101% of median Peak SWE.
Under the CODOS Dust Enhanced Runoff Classification (DERC) approach, WY2016 at Berthoud Pass has unfolded with AVG March 1st SWE, MIN Dust intensity, to-date, and, even though there were periods that could be considered as wet, overall AVG Spring precipitation, so far. In our March 1st Update we posted the following analysis of WY2016 that narrowed the DERC domain for Berthoud Pass to prior Water Years with AVG March 1st SWE:
Within the CODOS period of record at Berthoud Pass, WY2007 and WY2015 provide comparable options that meet the same criteria as found in WY2016. WY2007 is perhaps the best case since the onset discharge of WY2016 snowmelt at the USGS Fraser River at Upper Station gauge more closely mirror the WY 2007 hydrograph than WY2015 - which as you may remember from last year started off really slow and but had a big finish very late in the season.
Berthoud Summit SNOTEL SWE, Fraser River at Upper Station near Winter Park streamflow with CSAS SWE measurements. Snowpack is isothermal.
April 22 snow profile at the CODOS Berthoud Summit site. No dust observed.
Loveland Pass – April 22
The second snow profile at Loveland Pass this season was performed on April 22. No dust was observed. Any dust from D2 reported in the March Update, if present at all, would be extremely faint. The snowpack is just now approaching isothermal with an average snowpack temperature of -0.7° C. The CODOS measured SWE basically stayed the same at 19” between March 20 and April 22. At its max Grizzly Peak SNOTEL exceeded median Peak SWE by 2” (median value of 17.1” on median date April 12). It is currently 109% of median Peak SWE.
Under the DERC approach, WY2016 at Grizzly Peak SNOTEL has unfolded with AVG March 1st SWE, MIN Dust intensity, to-date, and like Berthoud Pass, even though there were periods that were wetter than normal, overall Spring precipitation is still considered AVG, so far. In our March 1st Update we posted the following analysis of WY2016 that narrowed the DERC domain for Berthoud Pass to prior Water Years with AVG March 1st SWE:
Within the CODOS period of record at Grizzly Peak, WY2015 is the only case in the AVG March 1st SWE domain. Even though WY2015 was categorized as AVG March 1st SWE, MIN Dust, and AVG Spring, the Spring precipitation timing and amount was atypical, this is seen in the sharp ascending limb of the hydrograph the end of May, 2015. In addition to utilizing WY2015 as a possible runoff scenario for WY2016, seeing how Grizzly Peak SNOTEL was 102% of median on March 1st and is currently 109%, other Water Years might be helpful indicators, with the best contender being WY2007 (High March 1st SWE, MIN Dust, AVG Spring) which has a hydrograph resembling the long-term median besides a couple of surges during the month of May.
Grizzly Peak SNOTEL and Snake River near Montezuma streamflow with CSAS measured SWE.
April 22 snow profile at Grizzly Peak CODOS site. No dust observed.
Looking south at the eastern edge of Arapahoe Basin Ski Area on April 22. No dust observed on surrounding landscape.
Looking easterly from Loveland Pass on April 22. Snow still covers majority of landscape in the surrounding area.
Looking Ahead
During the regular “Climate, Water and Drought Assessment” webinar sponsored by the Colorado Climate Center at Colorado State University (http://ccc.atmos.colostate.edu/) with support from the National Integrated Drought Information System (NIDIS), NOAA’s climate expert, Klaus Wolter, commented on what is possibly in store for the UCRB over the next few months. In the short term, the active storm track that we have been seeing will continue with a possible wet next 5-7 days before taking a break next week. Potentially we’ll see a cutoff low in our area in ~2 weeks. Please see updated 7-day precipitation, 1-month temperature, and 1-month precipitation forecast below.