NIDIS Intermountain West
Regional Drought Early Warning System
March 21, 2017

Precipitation


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).

Streamflow





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.

Temperature

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.

Outlook


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.
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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: March 21, 2017

Dry, warm, and windy conditions that dominated much of February have continued well into March.  Unlike February though (a typically dry month), average conditions in March are wetter, so moisture deficits are now growing faster.  Concerns are increasing as the region transitions from dry conditions during a normally dry time to dry conditions when springtime moisture should be ramping up.

And, while the higher elevations have overall fared better through most of the winter, snowpack this past week has shown signs of beginning the snowmelt season.  While above peak snowpack conditions is good news, early melting might not be good news.  Early melt could mean less overall water supply being saved, more evaporative loss to the atmosphere, and less replenishment to the soils.  It's too early to tell, but conditions are being closely monitored.  For now, melting has just started and streamflows have quickly responded, 13% of gages in the Upper Colorado River Basin reporting record high flows for this time of year.

Around the lower elevation plains, warm conditions have resulted in some early greenup and vegetation coming out of dormancy early. One of the bigger concerns is that any early vegetative growth can be damaged by spring freezes. The wind has contributed to high evaporative demand, and blowing dust, putting further stress on crops and soils.

Fortunately, outlooks show that the region may be prepping for a pattern shift.  While climate models are holding onto the probability of warmer than average temperatures to continue, there is more precipitation in the short-term forecasts and mid-term outlooks.  NOAA's Quantitative Precipitation Forecast (7-day QPF) is a bit aggressive, showing widespread accumulations of 2 to 4 inches over the plains, 1 to 2 inches over the mountains, and the Four Corners seeing the lowest accumulations of around half an inch.  The Climate Prediction Center also shows an increased chance of above average precipitation in the 8-14 day outlook.  If these forecasts hold true, we'd be looking at widespread relief and a drastic change over what the region has been experiencing for the past few weeks.

Recommendations

UCRB: Status quo is recommended.

Eastern Colorado: The current U.S. Drought Monitor (USDM) author has already proposed a slight expansion of D2, connecting the two separate D2 bubbles along the Front Range.  This proposed change is acceptable, but it's recommended that the rest of the region stay status quo.  At this time, widespread D1 still appears to be appropriate, with not as much justification evident for any more expansions of D2.  If the precipitation outlook pans out, it may even be possible to consider improvements next week.  On the flip side, if this active pattern misses any portion of the region, we could be looking at more degradations in the coming weeks.