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.

 

 


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).



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.


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.



EVAPOTRANSPIRATION



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 http://droughtmonitor.unl.edu/AboutUs/ClassificationScheme.aspx. 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.


FORECAST AND OUTLOOK

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.

Short Term: (7/19)

  • Rainfall totals may be generous across southwest and central Colorado between now and Tuesday with subtropical moisture being funneled into the region. Rainfall totals of over 0.50" are expected for the region between now and Friday morning. The southern Wasatch Range is likely to see over 0.25" of precipitation. Some light precipitation is likely for eastern Colorado. 
  • This weekend the west side of the basin will be dry. Afternoon thunderstorms will still be possible for most of the state of Colorado. These storms will be isolated and likely low precipitation cells. The San Juan Range continues to be the wettest anticipated location. 
  • Longer Term:
  • The 8-14 day precipitation outlook shows increased chances for below average precipitation for the Upper Green River Basin and extreme southeast Colorado. The rest of the basin and eastern Colorado are forecast equal chances of above and below average precipitation.  
  • The 8-14 day temperature outlook shows increased chances for above average temperatures for the entirety of the UCRB and eastern Colorado. These chances are highest in the southwest corner of the basin. 
  • The Climate Prediction Center July through September outlook shows equal chances of above an below average precipitation for the entirety of the UCRB and eastern Colorado. 
  • The seasonal drought outlook for Colorado and the UCRB shows no likely drought development over the next three months.

U.S. DROUGHT MONITOR

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: July 26, 2016

Looking back at the past week the region did have some monsoonally-generated precipitation.  This includes the San Juans, which is an area that is currently listed in D0.  There was also some good moisture out in northeastern Colorado.  Precipitation, month-to-date, shows most of eastern Colorado looking good, there are some dry spots along the northern Front Range.  Looking at the past 30 days we see that the northern front range and Sweetwater county has been a little below normal while the headwaters of the Duchesne Basin have been well below normal.  However, the Sweetwater county area is looking better long term while the Duchene Basin and the San Juans still shows a decrease in precipitation in both short term and long term time frames. 

 

Temperatures this past week in the Basin were fairly close to average.Temperatures weregreater than average east of the Continental Divide where we see temperature anomalies of 4-8 degrees.  Looking at month to date temperatures in the Basin have been cooler than average while out east the temperature anomalies decrease to 0-4 degrees above normal. 

 

Streamflow has come way down over the past few weeks as the spring supply of snowmelt and soil moisture diminishes.  The areas that are dry include the headwaters of the Green, headwaters of the Duchene and the headwaters of the San Juan. 

 

The Colorado River headwaters are looking pretty good, as well as the Yampa and White rivers.  Looking at our key indicator sites we have been falling in terms of stream flow.  This is very much the norm for this time of year but they have been falling a little more quickly than average.  You can especially see this along the Green River at Green River, UT and the San Juan near Bluff stations where they are now down into the 20th percentile. 

 

Reservoir levels are, for the most part, continuing to decrease.  After starting the year above the 90th percentile Flaming Gorge has now averaged out after releasing some water to Lake Powell.  Lake Granby is at near capacity, Blue Mesa is just a little above average but falling with the typical seasonal cycle.   McPhee is trending near seasonal average andNavajo has been draining over the last several months with some of that also contributing to Lake Powell.  Lake Powell did get a boost from Navajo and Flaming Gorge but is still well below average. 

 

Evaporative demand over the last 4 weeks shows hot spots over where it has been dry, not necessarily over the areas that have had above normal temperatures.  This can be seen looking at the Evaporative Demand Drought Index (EDDI) over the Duchene Basin.  This indicates that it is more likely vapor pressure deficit-drivenEvaporative demand for western and central Colorado is still below average on longer time scales.   

Vegetation across the UCRB is trending towards more stressed than average conditions. Soils are also drying, but still mostly in the normal range. The eastern half of Utah and much of southwest Colorado is showing pre-to-moderate drought. The Upper Green River Basin and the Yampa and White Basins are still in the normal-to-moist range. East of the divide, vegetation is mostly in the normal-to-moist range with respect to average. Larimer, Grand, and southeast Jackson Counties are in still in moderate drought as this area has not received normal precipitation.  

The ridge of high pressure will remain over the Great Basin through the remainder of the workweek bringing dry and hot conditions over the area. The ridge of high pressure will slowly shift east this weekend into early next week. This movement will allow showers and thunderstorms to develop this weekend.

 

Recommendations

UCRB: We are recommending expansion of D0 in northeastern Utah.  This expansion will include D0 covering Duchesne County and extending into central Uintah County.  This area has been continuing to dry out the past few weeks with SPIs of 0 to -1.5 going back six months.  Along with lower SPIs, VegDRI is showing drying out of vegetation in this area.  We are also recommending an area of D1 be upgraded from the current D0 area of Wasatch, Duchesne and Carbon Counties.  This area has dried significantly, 30 day SPIs show -1 to -2 and 90 day SPIs are 0 to -1.  VIC Soil Moisture Percentiles show Severe to Extreme drought and VegDRI is showing vegetation drying out in this area.  The U.S. Geological Survey is categorizing 7-day averaged streamflows in this area as much below normal.   

Eastern Colorado: Status Quo