NIDIS Upper Colorado River
Regional Drought Early Warning System
October 18, 2016

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.



Additional Precipitation Links: (will take you to an outside website)
AHPS Precipitation
High Plains Regional Climate Center's ACIS Maps

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).

Additional SNOTEL and Snowpack Links: (will take you to an outside website)
CBRFC Snow Conditions Map
NOHRSC Regional Snow Analyses: Central Rockies

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.

Additional SPI Links: (will take you to an outside website)
WestWide Drought Tracker SPI Maps

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.

Additional Streamflow and River Links: (will take you to an outside website)
USGS Streamflow Drought
CBRFC Peak Flow Forecast Conditions Map

The top left image shows VIC modeled soil moisture as a percentile ranking. The top right image shows satellite-derived vegetation from the VedGRI 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.

Additional Surface Water Links: (will take you to an outside website)
NLDAS Drought Monitor

The above images are of reference evapotranspiration (ET) from CoAgMet sites across Colorado. Reference ET assumes the amount of water that will evaporate from a well-irrigated crop. Higher ET rates occur during hot, dry, and windy conditions. Lower ET rates are more desirable for crops. See a map of locations for the above ET sites.

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.

The top two images show Climate Prediction Center's Precipitation and Temperature outlooks for 8 - 14 days. The middle image shows the 3 months Precipitation outlook. The bottom left image shows the Weather Prediction Center's Quantitative Precipitation Forecast accumulation for the seven days between Tuesday 12Z and ending Tuesday 12Z. The bottom right image shows the Climate Prediction Center's most recent release of the U.S. Seasonal Drought Outlook.


Next Week:

Wednesday-Friday: An upper-level low is spinning over the northwestern quadrant of the United States. Right now only the northern end of the basin is within the reach of cold air below this low pressure system, but on Thursday a cold front will drop through the center of the basin and northeast Colorado. This brings with it 15 degree cooler temperatures and a chance for 0.25-0.50" of precipitation for northwest Colorado. Eastern Colorado may see some precipitation as well, but the forcing for rain will be muted by downslope winds. 

The weekend and beyond: This weekend warmer, drier air settles in from the southwest. Look for slightly above average temperatures this weekend with isolated showers near the Four Corners. 

Longer Term: 

Precipitation: The 8-14 day outlook shows a slightly increased chance of below average precipitation for the UCRB and eastern Colorado. 

Temperature: The 8-14 day temperature outlook shows a substantial increase in chance of above average temperatures over the UCRB and eastern Colorado. These chances will be highest in eastern Colorado. 

Drought: Development of new drought is predicted as being unlikely for any given location in the Upper Colorado River Basin and eastern Colorado over the September through November time frame. The drought in eastern Colorado is predicted to improve.

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: October 18, 2016

A decent amount of precipitation fell across parts of northern UT and western WY last week.  Portions of the northern mountains of CO also received over half an inch of precipitation last week.  The remainder of the UCRB and the rest of Colorado received little to no precipitation for the week. Aside from some of the northern portions of the UCRB and around the San Juan mountains in southern CO, a drying trend has dominated the month of October for much of Colorado, east of the Continental Divide, and for the southern regions of the UCRB.

Short-term SPIs are positive for much of eastern UT and western WY with some drier SPIS (between 0 and -1) around the Four Corners region.  The recent dryness around CO is evident in the short-term SPIs with much of the Front Range between 0 and -1.5 on the 30-day SPI and as low as -2.5 to -3 in some locations on the 90-day SPI.

Abnormally warm conditions were observed around the entire region last week.  Warmer conditions are expected to continue.  HPC shows minor amounts of precipitation expected to fall across the northern portions of the UCRB.  Although the CPC shows above average precipitation more likely in the 8-14 day outlook, it is less likely that it will fully relieve some of the abnormally dry conditions that have recently shown up throughout eastern CO.



UCRB: Status quo is recommended for the UCRB.  The Four Corners region will be closely monitored over the next week for possible deteriorating conditions.  Although most of the SPIs for the region are positive for 90-days and longer, the 30-day SPI is showing some dryness.

Eastern Colorado: The current U.S. Drought Monitor author has spread the D0 throughout southeast CO on a recent draft of the USDM map based on short-term SPIs (black solid line).  The author also expanded the D1 along the Front Range to include Denver County, and parts of Jefferson and Douglas counties (maroon line).  We recommend that the D0 expansion include portions of northeast CO that have experienced similar recent dryness (black dashed line).  Although SPIs may not appear as bad in some areas, VegDRI does show the vegetative stress, and on-the-ground reports are that very warm and windy conditions have also contributed to a moisture deficit on crops in northeast CO.


**Disclaimer: The above recommendations are recommendations only, based on data, impacts, and input from local experts. These recommendations are sent to the U.S. Drought Monitor author on Tuesdays. The USDM author has sole discretion on final changes made in the region and can accept, reject, or modify the above recommendations and may have additional modifications. Additionally, any recommendations discussed during the NIDIS webinars that are agreed upon by the local experts and USDM author are still subject to change. Changes are final and official as of Thursday morning, and can be viewed on the official U.S. Drought Monitor website.

Additional Drought Index Links: (will take you to an outside website)
Palmer Drought Severity Index for Climate Divisions Updated Weekly
WestWide Drought Tracker's PDSI Updated Monthly
Surface Water Supply Index

When available, maps and text are updated Tuesday afternoons.

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