NIDIS Intermountain West
Drought Early Warning System
June 20, 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: June 20, 2017

Temperatures remained in the normal range for the Upper Colorado Basin for this time of year this week. Precipitation steered clear of the basin for the most part. The Upper Green River Basin and Uintah Mountains were the exceptions, and received over a quarter of an inch. Northern Sublette County received 1.00-2.00". Temperatures were a little above normal for eastern Colorado also with very little precipitation. Severe thunderstorms that fell early last week did leave a couple swaths of 0.25-0.50" of precipitation, but for the most part, eastern Colorado was also dry.

Longer term, much of the basin is still on the wetter side, especially in the mountains where the most moisture tends to fall. The valleys of far eastern Utah and far western Colorado are starting to return to drier than normal conditions on a six month timescale. Eastern Colorado is wetter than normal over the last six months, particularly in the Arkansas River Valley. In the South Platte Basin a few exceptions exist. Park County, and parts of Lincoln and Washington County are showing some long-term dryness.

Most high elevation snow has melted out, some hangs on to be sure. We are now past peak flow conditions along the Colorado, Green, and San Juan Rivers. We are enjoying the fruits of a good snow year capped off by May storms as streamflows are in the normal to above normal range for this time of year. Reservoirs are boasting healthy water supplies as well. Lake Powell is still below its long-term average, but higher than it has been in years. Short term dryness is being realized via lower than average soil moisture, and satellite-sensed dry vegetation conditions in the lower elevations, and southern portion of the UCRB. 

The south and central Rocky Mountains, as well as the southeast plans of Colorado, may see some meaningful precipitation totals at the end of this week as a cold front passes through. The rest of eastern Colorado and the UCRB will stay mostly dry. Weather prediction models are leaning towards warm, dry conditions returning thereafter, and persisting through next week. For now, water supplies look mostly fat and happy; things can change in a hurry this time of year. 

Recommendations

UCRB: Status quo: We kicked around the idea of D0 being expanded slightly on the western slopes of Colorado. SPIs and surface water conditions are consistent with those of the D0 pocket defined immediately to the west. Based on local expert feedback, we'll hold off.  

Eastern Colorado: Status quo is recommended. If recent dryness persists, northern Colorado could revert to D0 soon.