NIDIS Intermountain West
Drought Early Warning System
April 24, 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.

CSU Extension

I drove from Akron down to Garden City, KS today.  As I was driving I was observing conditions on the drive down 59, to 287 to 50.  North of I-70 wheat conditions are about what I would expect with the late plantings.  They are green but not growing fast as well.  We broke dormancy about 2 to 3 weeks ago.  South of I-70 you can tell that they are drier as you go farther south.  One thing I did notice is the inconsistency of stands in wheat.  You drive by 2 or 3 horrible looking fields stand wise and then you see some that look good but could use a rain.  Watching them I somewhat came to the conclusion that most of the fields with poor stands were probably more due to farming practices and several looked as if they were planted back to wheat in continuous cropping practices.  Continuous cropping wheat is generally much more risky than after fallow.
Once thing I did notice is the grass along the highway which is predominantly brome was under stress and wasn’t really a “good” color.  This shows that they haven’t really had a good rain in the last couple of months.  Traveling along hwy 50, even irrigated wheat looked poor which is confusing as they should have been irrigating that already with the dry conditions.  Once into Kansas, the wheat crop deteriorated as you went east.  Very poor stands were common and where you did see good stands you did see the discoloration of dry conditions.  One interesting sight was seeing a dryland wheat field that was much further along than most with really good stands and right across the road was a very poor field.  Even though they had a good stand, it was showing drought stress.  Much of the wheat is in a condition that if they don’t get a substantial rain in the next couple of weeks you probably can write it off for much if any yield potential.  The area of Kansas that I drove is in D2 but looks substantially worse than most of the wheat in Colorado in the D2 area.  Even though most of the wheat in Colorado appears to have been planted late, the root system isn’t highly developed and is struggling to grow fast enough to access moisture.
Pastures are dry but most of them are typically warm season grasses in that region and don’t break dormancy until May anyway.
Alfalfa has no flexibility at its crowns. Fields are being taken out. Conditions are similar to 2002.
Southwest Colorado
Allocations have been reduced by 20%. We're gearing up for wildfires.
Weld County
It's on the dry side, but not terrible. Wheat is okay. People have sprinklers on right now.
Otero County FSA
Little showers have been lifting our spirits, but the outlooks is still bad for dry land. Irrigated acreage and planting is being curtailed.
Kiowa County FSA
Wheat is struggling, but has perked up a bit. The next couple weeks will make or break the crop. It's not as bad as 2012. We are looking at status quo, D2.
Emery County FSA, UT
Soil moisture is awful. Winds have been strong, and we have been in the rain shadow for precipitation events.
Elbert County FSA
Soils are dry down to 4 or 5 feet deep. It has been windy and recent rains haven't done anything productive.
Lincoln County FSA
We have had a little rain to the south and snow to the north with lots of blowing wind and dirt.


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: April 24, 2018

Last week's exciting weather pattern brought excessive winds and warm temperatures, followed by a large moisture-rich system that dumped rain and snow across many parts of the Intermountain West.  Large areas of Wyoming and Colorado, along with some more isolated spots in Utah and New Mexico, received over half an inch of precipitation for the week.  The biggest disappointment is that larger accumulations weren't observed over the worst drought areas in eastern CO and NM, and little to no precipitation fell over the Four Corners, where D4 (exceptional drought) was recently introduced on the U.S. Drought Monitor.

High winds, warm temperatures, and low relative humidities have dominated much of the plains areas.  The result is that what little moisture is in the ground gets sucked up into the atmosphere, and fire danger has been extremely high.  Fires have been an issue in CO, NM, and UT.

For most of the higher elevations in the IMW, snowpack accumulation has peaked and melting has commenced.  For the northern basins, that meltoff is a bit more slow, with a few lingering snow events helping to delay it.  But snowmelt has been rapid in the southern basins.  Despite a better snow season in the northern basins, many areas still did not quite reach their average peak this year.  Runoff is less than average, and it's forecasted that water supplies will be below average this summer. The Upper Green basin in WY remains the Upper Colorado River Basin's one area of good conditions. To the south, the situation is much more bleak.  Dust is a major concern in the San Juan mountains.  In addition to low snowpack peaks, runoff is in poor shape, melting will likely be completed a month earlier than normal, and water supply forecasts are much below average.

As we progress through spring, we enter the "wet" season for much of the eastern plains.  For these areas, a soaking event like what we saw last week should be typical.  Events that drop half an inch of moisture are expected this time of year, and while they may delay further deteriorating drought conditions, they are not beneficial enough to eliminate impacts or improve drought conditions.  For areas around the Four Corners and the higher elevations currently in drought, they are now entering their "drier" time of year.  The chances of chipping away at drought during the dry season are slim, and those who reside in those areas will likely have to wait till the kick-off to monsoon season to see large scale relief.

On a positive note, the Climate Prediction Center is showing that the Southern Plains drought area (which extends into eastern CO and NM) has a good chance of above average precipitation on the 3-4 week time scale.  Unfortunately, with a summer seasonal outlook showing warmer than average conditions likely, summer water demands are likely to be high, putting stress on a vulnerable water supply and further stressing already struggling crops and rangelands.


Improvements: Areas outlined in blue are recommended to show 1-category improvements to their U.S. Drought Monitor categories.  For all these areas, long-term SPIs are more marginal (on the edge of a specific D-category possibly), and they've received enought month-to-date moisture to justify improvements.  In Utah, D3-to-D2 improvement areas have received 2 to 4 inches of moisture in April.  In Colorado, D1 and D0 areas recommended for improvement are mostly showing near, to slightly below, normal SPIs any different timescales, and have received 2 inches or more of moisture since the beginning of April. 

Deteriorations: Areas outlined in black are recommended for expansion to D3 drought conditions.  All areas are reporting very strong and damaging winds sucking moisture out of the ground, many fires, wheat and grasses are struggling, and irrigated lands are struggling as well.  Higher elevation areas are bare of snow or SNOTEL is reporting less than 5th percentile snowpack (with many showing 0 percentile precipitation water-year-to-date). The black striped areas outlined in gray have already been proposed for D4 expansion by the U.S. Drought Monitor author.  These areas received little-to-no precipitation in the most recent storm event that passed over last weekend.  While short-term SPIs aren't as bad, these proposed D3 and D4 expansion cover areas where longer-term SPIs (particularly at the 6-month time scale) are less than -2.