NIDIS Intermountain West
Drought Early Warning System
February 20, 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 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.

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.

Montezuma County Extension

Precipitation has barely been measurable.  Most predictions are irrigation water will be full supply due to holdover from previous years.  The Winter Wheat crop has failed and tops soil moisture is very low.  Impacts are mainly expected to dryland and rangeland.  The farther south in the county, the drier it is.  It is expected that D3 will move into SW Colorado soon, but feel it is a bit early for D3.  D2 is bad enough as it is.


Western Colorado Extension

The dryness in the lower elevations is very concerning in the Grand Valley and down towards Montrose.  They did get a decent storm, but very windy with dirty snow.  The lower elevations were seeing gusts of over 50 mph, blowing dust and snow.  Soils are very dry.  The surface has gotten wet a few times, but it's not enough to go deeper.  Teetering on the D2 to D3.


Center for Snow and Avalanche Studies in Silverton, CO

The recent snow storm brought much needed snow.  The storm was accompanied with strong southwest winds.  The winds before and during the snow brought a notable dust event.  The dust appears to be significant and widespread across the range which will most likely bring future hydrologic consequences.  This is the first major dust even of the season, which is climatologically early.


Dolores County Extension

Dry.  The recent storms have helped a little bit for topsoil, but did little to help the soil moisture deficit.  Winter wheat crop is history and there is a lot of concern about planting spring crops on dryland.  It is probable there may be no dryland crops planted this spring if this keeps up.  The lower lying rangeland to the west is in very tough shape.  Unable to maintain snow cover and the recent winds are not helping anything except relocating some topsoil.  Montezuma County is in better shape as the storms favored the area more than Western Dolores County


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: February 20, 2018

Last week the Upper Colorado River Basin saw a mix of precipitation.  The higher elevations in western Colorado and central Utah received widespread amounts between 0.50 inches up to 2.00 inches.  Some isolated areas in the highest elevations of the San Juan Mountains along the Divide received up to 4.00 inches.  This may have been the best week in the San Juans this season, however, this is near average for this time of the season and deficits are still quite high.  Elsewhere in the UCRB, mainly the lower elevations, precipitation amounts were below 0.50 inches.  Southwest Colorado remained drier than average for this time of year.  Continuing the pattern of below normal precipitation.

Eastern Colorado was mostly dry this week, with much of the area receiving less than 0.10 inches of new precipitation.  The Front Range from Larimer County to El Paso County saw a nice snow storm Sunday evening through Monday, dropping between 0.10 inches to 0.5 inches of liquid, the highest amounts were in Boulder County.

Despite the bump in precipitation, Water Year Precipitation Percentiles from SNOTEL sites in southern and western Colorado and Utah remain in the single digits, with most below the 5th percentile.  Snowpack did see an increase the last week, however it was a near normal increase for this time in the season.  The percent of normal for some basins did increase, but remain much below normal.

Temperatures through the UCRB and Intermountain West region, with the exception of northern Wyoming, were at least 3 degrees above normal.  Southeastern Colorado saw temperatures 6 to 9 degrees warmer than normal.  Obviously, this did not help conditions.

The precipitation in the higher elevations will help hold off any degradations this week, but it wasn't enough to improve conditions.  Since the lower elevations in southwest Colorado missed the best precipitation, and what did fall is not going to help, D3 is warranted. 


UCRB:  We are recommending introducing D3 in southwest Colorado and into southeast Utah and northwest New Mexico.  This area is seeing very low SPIs (-1.5 to -2 and below) on the 90-day out to the start of the water year and going out 6 and 9 months.  SNOTEL snowpack and precipitation percentiles are in the single digits for this area, some of the lowest years on record going back 30+ years and numerous sites.  Due to the prolonged dryness and high temperatures, the winter wheat crop in southwest Colorado has failed and soils are drying out.  What little precipitation has fallen has not helped.  Ag impacts this season should be limited to dryland and rangeland.  Since this drought is following a few good years, water supply is in good shape and irrigation water should be in full supply. 

Some of our on the ground reports suggest D3 is imminent, but it might be a little bit soon to go for it.  The Colorado Climate Center feels D3 is justified based on the data and low snowpack. 

Eastern Colorado: Status quo.