NIDIS Intermountain West
Drought Early Warning System
December 11, 2018


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 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.

NWS Grand Junction, CO

Western slope water use for agriculture has settled down. Still have a long way to go to make up for this long-term drought.


Central UT, FSA

The drinking water shortages are still a concern because the stream levels were so low.  "Even though the flows bump for a day or two in the Muddy the stream flow itself continues to fall which is very concerning. We do have an ice tunnel insulating the creek for now which will keep it flowing but we are far from out of the woods both for vegetation and drinking water". 


Durango CO, Emergency Managment

October and November storms did little to improve conditions, still "dire down here".  Cloudy most everyday.  Ski areas are doing fine.


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 11, 2018

Over the last week, most of the Intermountain West followed the recent temperature trend, and temperatures were cooler than average, with near average temperatures in southern Arizona and New Mexico. Wyoming was especially cold with most of the state seeing 3 to 6 degrees below average and localized areas less than 12 degrees below average for the last week.

Much of the region was dry over the last week. Precipitation was mostly concentrated along the northern portion of the Continental Divide in Colorado through southern Wyoming and in the far southern part of the IMW in AZ and NM. Precipitation totals along the higher elevations were closer to average for the Colorado mountains and a little less than average for the UT and WY mountains. The eastern plains and low elevations of the IMW were dry, which is typical for this time of year.

Snowpack totals continue to improve as we progress through December. South Platte, Colorado, Yampa, White, and North Platte River Basin are all above average. However, to the south, the San Juan River Basin still shows snowpack below average. In Wyoming, Wyoming Range and Wind River Range, snowpack did not show a significant improvement, not bad but could be better. Central Utah saw snowpack totals continuing to improve, most areas improving to the mid 70’s which could indicate a step in the right direction. 

Month-to-date shows most of the Intermountain West drier than average, but the cooler than average temperatures we have been having help to offset this.

The next week does not appear to be an active one. Looking at the 7-day forecast most of the Intermountain West will receive very little to no precipitation. Forecasted precipitation is centralized along the Divide where 0.10-0.50” is expected. Warmer than average temperatures are also expected to return for the next couple of weeks.



Much of the Intermountain West received little to no precipitation in the last week so we are recommending status quo for the Upper Colorado River Basin as well as eastern Colorado.

UCRB:  Status quo 

Eastern CO:  Status quo