NIDIS Intermountain West
Regional Drought Early Warning System
February 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: February 21, 2017

It was another warm week for the Upper Colorado River Basin and eastern Colorado. Temperatures were 6-12 degrees above normal for most of the basin with some pockets closer to normal in southwest Wyoming and in southern Utah near Lake Powell. Temperatures were 6-12 degrees above normal for southeast Colorado, and 12-18 degrees above normal for northeast Colorado as cold winter air continues to be confined at higher latitudes. 

The first part of the week was relatively calm with westerly winds returning to the basin last Friday through the weekend. This allowed for some precipitation in the basin, but mainly just wind east of the divide save for some spotty showers on Sunday night. The high elevations of the UCRB managed 0.25-0.50" of precipitation over the last week for the most part. Some of the lower-to-middle elevation areas, such as La Plata County and eastern Montezuma County in Colorado, and northern Emery County and Carbon County in Utah, received 0.50-1.00" or more. 

Despite the unseasonably warm weather, high elevation snowpack is still well above average for most areas across the basin and east of the divide. Snowpack in eastern Utah and southwest Wyoming is particularly high. The Yampa Basin and North Park areas in northwest Colorado are closer to average.

The unseasonably warm weather has led to increased snowpack oblation at lower and middle latitudes of the Upper Colorado River Basin, and thawing of river channels. This, and a wet January, have paved the way for higher than average flows in the UCRB. 45% of non-frozen gages are reporting in the above normal range, and 23% are reporting much above normal. Lake Powell is still storing less water than its climatological average for this time of year. Other major reservoirs in the basin are reporting storage in the normal, or above normal range. Navajo Reservoir has seen an early upswing in storage this year, and is now at 104% of average storage. Soil moisture remains a concern for eastern Colorado as spring rains will be needed to make up for deficits during the second half of last growing season. 

After a month of well above average temperatures for most of the basin, a substantial cool-down appears to be on the way, and forecast models are indicating that the cooler weather may stick around for a while once it hits (see outlook for details). The storm appears to be most likely to make the UCRB richer with widespread totals of over an inch forecast across the Tetons, Wasatch, Uintahs, and western Colorado for the next week. Unfortunately, it could make eastern Colorado poorer as this storm will likely be more of a wind event out on the plains. 

Recommendations

UCRB: Status Quo. No drought here.

Eastern Colorado: It is recommended that D2 be extended in western Lincoln County to include southern and central Lincoln County. Karval is showing similar long-term deficits to Limon, and reports on the ground have verified a gradient in conditions between Karval and Rocky Ford. Conditions are still on the dry side for Rocky Ford, but not as bad as immediately north. 

It is recommended that D0 be removed from the Sangre De Cristo Range on the border of Saguache and Custer County. SNOTEL stations in this area have shown lower water year to date precipitation percentiles than their nearby counterparts, but have caught up into the normal range. Snowpack here is also above average.