NIDIS Intermountain West
Drought Early Warning System
May 16, 2017


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.

Standardized Precipitation Index

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.

Snotel and Snowpack

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).


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.

Surface Water

The top left image shows VIC modeled soil moisture as a percentile ranking. The top right image shows satellite-derived vegetation from the VegDRI 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.

Evaporative Demand

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 Weather Prediction Center's Quantitative Precipitation Forecast accumulation for seven days. The bottom left image shows the 3-month precipitation outlook from Climate Prediction Center, and the bottom right image shows the Climate Prediction Center's most recent release of the U.S. Seasonal Drought Outlook.

Summary and Recommendations

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.

Summary: May 16, 2017

The past week in the UCRB brought less than 0.10" of new precipitation in southwestern Wyoming and northeastern Utah and between 0.25 and 1.00" in western Colorado.  The highest precipitation amounts in the basin fell in the San Juan Mountains and into the southwest corner of the state and in Rio Blanco County, seeing up to 1.00".  Mesa, Delta, Eagle and Grand counties were drier seeing less than 0.25" last week.  Most of these amounts in the basin were near to slightly below normal.  Below normal precipitation in the valleys of the UCRB has been a trend since mid-winter.  Most SPIs in the lower elevations are showing up in the 0 to -1 range for the past 30 days and down to the -2 SPI for the past 90 days showing some short-term dryness.

Temperatures last week through the basin were once again above normal, leading to continued melting of the snowpack.  Despite the warm temperatures and melting snowpack, streamflows in western Colorado remain mostly in the normal to above normal range.  Along the western edge and northern portion of the basin, streams are seeing much above to record high streamflows for the past 7 days.

Eastern Colorado saw a very nice shot of precipitation early in the week with totals ranging from 0.5" to 4.00".  The highest amounts show up in the Arkansas Valley, from Huerfano to Cheyenne County, where the entire area received at least 2.00" last week.  The rest of eastern Colorado saw at least 0.5" with the exception of Park, Jackson and northern Larimer counties.

The recent precipitation has brought most SPIs for all time scales to the positive side of the scale, indicating near to above normal precipitation.  Park County is still showing dry SPIs for 30 and 90-days and 6-months, which justifies the D0 and D1.  Larimer County is still showing dry 90-day SPIs, justifying the D0.

Temperatures in eastern Colorado were above normal for last week, contributing to snowmelt.  Streamflows have increased, especially in the Arkansas River and tributaries to much above normal and record high, thanks to the precipitation last week and continued snowmelt.  Other streams in eastern Colorado remain near normal.


UCRB: The Drought Monitor Author has recommended some expansion of D0 in Mesa, western Montrose and western Delta counties due to the short term dryness in the valleys and early loss in snowpack.  The Colorado Climate Center agrees with this recommendation.  We will also recommend some further expansion of D0 in the valley of Delta and Montrose counties due to similar conditions.

Eastern Colorado: It is recommended that D1 be removed from Boulder, Gilpin, Clear Creek, extreme northeast Park, Teller, Douglas and Jefferson counties.  This area received a few bouts of beneficial precipitation early last week.  Much of Park County remains dry, so the D1 should stay there.

No further improvements at this time due to longer-term dryness.  We will re-evaluate next week.