NIDIS Upper Colorado River
Regional Drought Early Warning System
September 27, 2016

The images above use daily precipitation statistics from NWS COOP, CoCoRaHS, and CoAgMet stations. From top to bottom, and left to right: most recent 7-days of accumulated precipitation in inches; current month-to-date accumulated precipitation in inches; last month's precipitation as a percent of average; water-year-to-date precipitation as a percent of average.



Additional Precipitation Links: (will take you to an outside website)
AHPS Precipitation
High Plains Regional Climate Center's ACIS Maps

The top left image shows the Natural Resources Conservation Service's SNOTEL water-year-to-date precipitation percentile rankings. The top right image shows sub-basin averaged snow water equivalent accumulations as a percent of average. The images below show accumulated snow water equivalent in inches (green) compared to average (blue) and last year (red) for several different sub-basins across the UCRB (and were created by the Colorado Basin River Forecast Center).

Additional SNOTEL and Snowpack Links: (will take you to an outside website)
CBRFC Snow Conditions Map
NOHRSC Regional Snow Analyses: Central Rockies

Standardized Precipitation Index standardizes precipitation accumulations for a specified time period into percentile rankings. -1.0 to -1.5 is equivalent to a D1 to D2. -1.5 to -2.0 is equivalent to a D2 to D3. -2.0 and worse is equivalent to a D3 to D4. 30- and 60-day SPIs focus on short-term conditions while 6- and 9-month SPIs focus on long-term conditions. SPI data provided by High Plains Regional Climate Center.

Additional SPI Links: (will take you to an outside website)
WestWide Drought Tracker SPI Maps

The top left image shows 7-day averaged streamflows as a percentile ranking across the UCRB. The top right image shows 7-day averaged discharge over time at three key sites around the UCRB: The Colorado River at the CO-UT state line; the Green River at Green River, UT; and the San Juan River near Bluff, UT. All streamflow data provided by United States Geological Survey.

Additional Streamflow and River Links: (will take you to an outside website)
USGS Streamflow Drought
CBRFC Peak Flow Forecast Conditions Map

The top left image shows VIC modeled soil moisture as a percentile ranking. The top right image shows satellite-derived vegetation from the VedGRI product (which updates on Mondays).

The graphs shown below are plots of reservoir volumes over the past full year and current year to date (black). The dashed line at the top of each graphic indicates the reservoir's capacity, and the background color-coded shading provides context for the range of reservoir levels observed over the past 30 years. The data are obtained from the Bureau of Reclamation. Some of the reservoir percentiles don't line up at the new year due to differences in reservoir levels at the beginning of 1985 and the end of 2014.  Dead storage has been subtracted. Note: Lake Granby data are obtained from the Colorado Division of Water Resources, and only goes back to the year 2000.

Additional Surface Water Links: (will take you to an outside website)
NLDAS Drought Monitor

The above images are of reference evapotranspiration (ET) from CoAgMet sites across Colorado. Reference ET assumes the amount of water that will evaporate from a well-irrigated crop. Higher ET rates occur during hot, dry, and windy conditions. Lower ET rates are more desirable for crops. See a map of locations for the above ET sites.

The above images are available courtesy of NOAA’s Evaporative Demand Drought Index (EDDI). Drought classification listed is a function of the depth of reference evapotranspiration accumulated over a given period of record with respect to a climatology of 1981-2010. The drought categories displayed are in line with the US Drought Monitor's Percentile Ranking Scheme Data used to generate these maps come from the North American Land Data Assimilation System Phase-2 (NLDAS-2) project, which assimilates observations of temperature, wind speed, radiation, and vapor pressure deficit. The date indicates the last day of the period of record, and the week number indicates the window size for the period of record..

All images show temperature departures from average over different time periods (last 7 days on top left; month-to-date on top right; last full month on bottom). Temperature departure maps provided by HPRCC ACIS.

The top two images show Climate Prediction Center's Precipitation and Temperature outlooks for 8 - 14 days. The middle image shows the 3 months Precipitation outlook. The bottom left image shows the Weather Prediction Center's Quantitative Precipitation Forecast accumulation for the seven days between Tuesday 12Z and ending Tuesday 12Z. The bottom right image shows the Climate Prediction Center's most recent release of the U.S. Seasonal Drought Outlook.


Next Week:

Wednesday-Friday: Moist, southerly flow is bringing favorable conditions for rainfall over the basin between Wednesday and Friday. Southwest Utah and Western Colorado are expected to receive 0.25-1.00" of rainfall over this time frame. The northern end of the basin in southwest Wyoming will be dryer with any new rainfall confinded to higher elevations.

The weekend and beyond: Over the weekend the moist, southerly flow retreats, and light, westerly flow takes over. Southern Wyoming and northeast Colorado may be favored for patchy rainshowers with accumulations mostly less than 0.10". Early next week a cooler airmass will move in from the northwest. This is expected to bring much cooler temperatures to the UCRB. Precipitation totals won't be substantial, but will it will likely fall as snow above 8000ft. 

Longer Term: 

Precipitation: The 8-14 day outlook shows an increased chance of above average precipitation for the UCRB and eastern Colorado. These chances will be strongest in the northern portions of the UCRB and eastern Colorado. 

Temperature: The 8-14 day temperature outlook shows an increased chance for below average temperatures in the basin. These chances will be strongest in the north and west portions of the basin. Below average temperatures are slightly favored east of the divide as well, but not to the same extent as in the basin. 

Drought: Development of new drought is predicted as being unlikely for any given location in the Upper Colorado River Basin and eastern Colorado over the September through November time frame. The drought in eastern Colorado is predicted to improve.

Above is the most recent release of the U.S. Drought Monitor map for the UCRB region.
Below shows the proposed changes for this week, with supporting text.


UCRB Improvements: It is recommended that the drought in the western portion of the Upper Colorado River Basin be improved by one category. Unseasonably high moisture totals in this region have shifted SPIs from negative to positive even on six month timescales. The benefits of this can be readily seen in the soils and streams. Please keep the D0 to the east of western Moffat, Rio Blanco, and Garfield Counties in Colorado and to the north of southern Lincoln County in Wyoming.  These improvements appear to translate well to northwest Utah outside of the UCRB. 

UCRB Degradations: It is recommended that D0 be added to southern Routt, Eagle, northern Pitkin, and extreme northeast Garfield Counties. This area has received below average seasonal precipitation in the high elevations, which has translated to some troublingly-low streamflows. 

Eastern Colorado: Status Quo

Summary: September 27, 2016

The last week brought tropical remnant moisture northward into the western fraction of the Upper Colorado River Basin, leading to some strong and very welcome rainfall activity. The UCRB from the Green River westward, and up into Uintah, Daggett, and Sweetwater Counties was blanketed with over an inch of fresh rain. Much of the area, especially at higher elevations, received 2.00-4.00". This was sufficient for bringing water year precipitation totals for the area up to or above normal. Totals farther east in the basin tapered, but still generally had a good showing, coming in between 0.50" and 1.00". The upper elevations of the San Juans received over an inch.  

Conversely, the past week in eastern Colorado, the San Luis Valley, and the far eastern fringes of the UCRB was dry with temperatures 2-6 degrees above average. Most of the eastern half of the state received less than a quarter of an inch of new precipitation save for central Kit Carson County and the Costilla-Huerfano County border. Even most of Grand, Eagle, and Summit County in the UCRB received less than a quarter of an inch. 

Streamflows responded very positively to the past week's rain across the southern and western portions of the UCRB. Flows just last week in the Duchesne River Basin were below average, and are now much above average. Below normal flows still exist in the headwaters of the Green River and Yampa River as well as some smaller tributaries such as the Eagle River and Beaver Creek. Major reservoirs have not yet seen an appreciable bump in storage from these increased flows, but Lake Powell is expected to become the primary beneficiary. 

Two weeks ago root zone soil moisture was well below the normal range across the west and northwest parts of the UCRB. According to the Variable Infiltration Capacity (VIC) Model soils have bounced back into the normal range over the past two weeks, and are now above average in the southwest portion of the UCRB. The VIC model is indicating a few drier than average patches of root zone soil in the UCRB. These are located in the headwater portions of the Yampa and Colorado Rivers. East of the divide root zone soil moisture is by and large in the normal range. The biggest exception to this is southern Lincoln, Otero, and Crowley Counties. Soil moisture is estimated as ranking in the 10th to 20th percentile for late September in this region. 

Satellites indicate that the past week's rains has brought with it a greening of vegetation in the western portion of the basin. This improvement is most noticeable in Duchesne and Uintah Counties. Vegetation conditions are still indicative of moderate drought along the Wasatch Range. The San Juans and southern Utah are holding on to some drier than average vegetation conditions as well. East of the divide vegetative health conditions are reflective of pre-and-moderate drought up and down the Front Range as well as across the east-central plains. The VegDRI satellite product is currently depicting the eastern and southeastern fringes of Colorado as moister than average. 



**Disclaimer: The above recommendations are recommendations only, based on data, impacts, and input from local experts. These recommendations are sent to the U.S. Drought Monitor author on Tuesdays. The USDM author has sole discretion on final changes made in the region and can accept, reject, or modify the above recommendations and may have additional modifications. Additionally, any recommendations discussed during the NIDIS webinars that are agreed upon by the local experts and USDM author are still subject to change. Changes are final and official as of Thursday morning, and can be viewed on the official U.S. Drought Monitor website.

Additional Drought Index Links: (will take you to an outside website)
Palmer Drought Severity Index for Climate Divisions Updated Weekly
WestWide Drought Tracker's PDSI Updated Monthly
Surface Water Supply Index

When available, maps and text are updated Tuesday afternoons.

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