NIDIS Intermountain West
Drought Early Warning System
December 10, 2019


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. Colors match the different drought categories with the U.S. Drought Monitor. 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 above image shows SNOTEL snowpack percentiles for each SNOTEL site in the Intermountain West. 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.

Condition Monitoring and Impacts

Map of current condition monitoring reports submitted to CoCoRaHS in the last week overlaid on the current U.S. Drought Monitor depiction. Specific impacts reports from local experts listed below.


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: December 10, 2019
Over the last week the Intermountain West received some beneficial precipitation, especially in the Colorado higher elevations.  Some areas to note include the San Juan Basin up north thru the Gunnison Basin received 1.01-2.00” of precip with NE Montezuma County seeing 2.01-3.00”, Routt and Jackson Counties received 0.51-2.00” and southwest Utah saw 1.01-2.00”.  This precipitation over the last week has helped increase SWE in SW Colorado.  For instance, Gunnison River Basin is now 111% of median and San Miguel River Basin is 131% of median.  However, recent precipitation was not enough to make up the huge deficit from the lack of Monsoon season.  For instance, looking at the two examples given precipitation at Gunnison River Basin is 77% for the water year and San Miguel River Basin is at 65%.

Temperatures were mostly above normal across much the IMW, with the exception of NW Utah and SW Wyoming where it was 0 to 3 degrees below average.  The whole state of Colorado experienced above average temperatures of at least 3 to 9 degrees with some pockets of 9 to 15 degrees above average in south central CO.  

Streamflows across the Upper Colorado River Basin are running above normal for the most part.  Reservoirs in the Upper Colorado River Basin are retaining adequate winter storage. Lake Powell, of course, is still below the long-term average. Most major reservoirs, however, are retaining near-normal to above normal storage thanks to last year's great snowpack.

Forecast outlook is showing some spotty/higher elevation precipitation in northern Utah and western Colorado.  It appears the most significant precipitation will occur along the Wyoming/Idaho boarder where they are forecasting up to 3.00”.  Southern Utah, most of Wyoming, and eastern Colorado are expected to see little to no precip this upcoming week.  Temperatures are expected to be below average for Utah, normal temperatures forecasted for the rest of the IMW, and above average temperatures expected in eastern Colorado. 


Utah:  Status Quo.  We are in agreement with the Utah drought representatives on status quo.  Last week’s precipitation was not enough to improve the deficit.  Some specific observations include:
Wasatch Front: rainfall at lower elevations rather than more useful snowfall
Emery County: lower elevations typically green up with Sept/October rains, that didn't happen this year; producers are still hauling water. PRISM data in Emery County is consistently not representative of conditions. We hypothesize that this is due to the sparsity of weather stations in the area and the stations that do exist being located at high elevations.

Four Corners: Status Quo.  While much of the IMW saw beneficial precip, including the four corner region, it was not enough to improve a full drought category.  However, recent precipitation is pushing us in the right direction.  A few weeks ago we were teetering on the edge of downgrading from D2 to D3 and now we are teetering on an improvement from D2 to D1 but we are not quite there yet.  30-day SPIs are showing great improvement in the four-corners/San Luis Valley area however, fast forward to 90-day, 120-day, and the 6 month timeframes and the SPIs deteriorate significantly.  Precipitation is still behind for the water year in much of this area.  Mesa Verde NP, for example, is still tied for its record driest July 1 - present precipitation accumulations, and running at a 5-inch deficit.

Eastern Colorado:  Status Quo.  Most of eastern Colorado was dry over the last week with the exception of the northern Front Range.  30 day SPIs are showing improvement around Teller County but this area did not receive precipitation and experienced above average temperatures over the last week.  We decided to hold off on improvements in this area but will keep an eye on things for next week.