162  
FGUS76 KPQR 072251  
ESFPQR  
 
WATER SUPPLY OUTLOOK  
NATIONAL WEATHER SERVICE PORTLAND OR  
350 PM PDT APRIL 7 2021  
   
..OREGON WATER SUPPLY AND SPRING FLOOD OUTLOOK AS OF APRIL 7 2021
 
 
THE WATER SUPPLY FORECAST FOR THE SPRING AND SUMMER OF 2021 IS BELOW  
AVERAGE FOR MOST OF OREGON, WITH THE EXCEPTION OF NEAR-AVERAGE  
FORECASTS FOR PORTIONS OF NORTH-CENTRAL AND NORTHEAST OREGON AND  
ABOVE-AVERAGE FORECASTS FOR FAR-NORTHEAST OREGON. REGARDING THE RISK  
OF SPRING SNOWMELT FLOODING, THERE IS A SLIGHTLY-ENHANCED RISK OF  
FLOODING FOR PORTIONS OF NORTHEAST OREGON DUE TO ABOVE-AVERAGE  
SNOWPACK. SPRING FLOODING IS UNLIKELY ELSEWHERE EAST OF THE CASCADES  
DUE TO LONG-TERM SOIL MOISTURE DEFICITS AND LOW WATER YEAR  
PRECIPITATION. SPRING FLOODING IN CENTRAL AND EASTERN OREGON IS  
TYPICALLY CAUSED BY A COMBINATION OF RAINFALL AND RAPID SNOWMELT.  
SPRING SNOWMELT FLOODING HAS HISTORICALLY NOT OCCURRED FOR RIVERS  
WEST OF THE CASCADES AND IS NOT EXPECTED THIS YEAR.  
 
NOTE THAT WATER SUPPLY FORECASTS ARE PARTICULARLY LOW FOR MUCH OF  
SOUTH-CENTRAL OREGON, INCLUDING KLAMATH AND LAKE COUNTIES. MOST  
AREAS PROJECTED TO BE BELOW AVERAGE ARE ALREADY DROUGHT STRESSED DUE  
TO DRY CONDITIONS THE PAST 18 MONTHS. RECENT DRY CONDITIONS IN MARCH  
AND EARLY APRIL HAVE RESULTED IN FURTHER REDUCTIONS IN THE WATER  
SUPPLY FORECASTS FOR THE SPRING AND SUMMER.  
 
BASED ON CONDITIONS AND SEASONAL FORECASTS, THERE ARE LIKELY TO BE  
SIGNIFICANT AND WIDESPREAD DROUGHT IMPACTS THIS SUMMER, INCLUDING  
STRESSED VEGETATION, INCREASED FIRE DANGER, REDUCED AVAILABILITY OF  
WATER FOR IRRIGATION, LOW STREAMFLOW AND WARM WATER TEMPERATURES  
WHICH NEGATIVELY IMPACT FISH HABITAT, AND POOR RANGELAND CONDITIONS  
FOR LIVESTOCK AND WILDLIFE GRAZING.  
 
REFER TO THE SECTIONS BELOW AND LINKS PROVIDED FOR DETAILS REGARDING  
SNOWPACK, PRECIPITATION, SEASONAL CLIMATE OUTLOOKS, RESERVOIRS,  
STREAMFLOW, WATER SUPPLY FORECASTS, AND SPRING FLOOD POTENTIAL.  
 
THE NEXT UPDATE TO THIS OUTLOOK WILL BE ISSUED BY MAY 5, 2021.  
 
____________________________________________________________________  
PRECIPITATION AND TEMPERATURES ACROSS OREGON  
 
PRECIPITATION FOR THE 2021 WATER YEAR THUS FAR (OCT 1, 2020 THROUGH  
APRIL 6, 2021) RANGES FROM 55 TO 90 PERCENT OF AVERAGE IN OREGON.  
THE LOWEST TOTALS RELATIVE TO AVERAGE HAVE BEEN IN CENTRAL, SOUTH-  
CENTRAL AND SOUTHEAST OREGON, AREAS THAT HAVE ALSO BEEN BELOW  
AVERAGE FOR MUCH OF THE PAST TWO YEARS.  
 
MARCH PRECIPITATION WAS BELOW AVERAGE STATEWIDE AND ESPECIALLY DRY  
FOR NORTH-CENTRAL, SOUTH-CENTRAL AND SOUTHEAST OREGON. LARGE SWATHS  
OF CENTRAL AND EASTERN OREGON HAD LESS THAN A QUARTER INCH OF  
PRECIPITATION IN MARCH. THIS SIMULTANEOUSLY INCREASED CONCERNS ABOUT  
DROUGHT AND REDUCED THE THREAT OF SPRING SNOWMELT FLOODING.  
 
MARCH TEMPERATURES WERE ALSO BELOW AVERAGE, GENERALLY 1 TO 3 DEGREES  
BELOW NORMAL. WHILE THE LACK OF PRECIPITATION INCREASED DROUGHT  
CONCERNS, THE COOL TEMPERATURES AT LEAST HELPED TO REDUCE AND DELAY  
MELTING OF THE MOUNTAIN SNOWPACK. WITH WARMER TEMPERATURES THE FIRST  
WEEK OF APRIL, SPRING SNOWMELT HAS BEGUN FOR MANY AREAS OF THE STATE.  
 
FOR ADDITIONAL DETAILS ON PRECIPITATION AND TEMPERATURES:  
 
NOAA NATIONAL WEATHER SERVICE - NORTHWEST RIVER FORECAST CENTER  
WWW.NWRFC.NOAA.GOV/WATER_SUPPLY/WY_SUMMARY/WY_SUMMARY.PHP  
 
NOAA NWS - CALIFORNIA-NEVADA RIVER FORECAST CENTER (KLAMATH BASIN)  
WWW.CNRFC.NOAA.GOV/WATER_RESOURCES_UPDATE.PHP  
 
____________________________________________________________________  
SNOWPACK ACROSS OREGON  
 
AS OF EARLY APRIL, MOUNTAIN SNOWPACK IS BELOW AVERAGE FOR THE  
SOUTHERN HALF OF THE STATE AND NEAR TO ABOVE AVERAGE FOR THE  
NORTHERN HALF. AFTER DRAMATIC SNOWPACK INCREASES IN FEBRUARY, THERE  
WAS NOT MUCH CHANGE IN SNOWPACK IN MARCH, WITH GENERALLY DRY AND  
COOL CONDITIONS. MOST SNOW MONITORING STATIONS HAVE SHOWN  
SIGNIFICANT, EVEN DRAMATIC, MELT IN EARLY APRIL DUE TO WARMER  
TEMPERATURES.  
 
ADDITIONAL SNOWPACK INFORMATION:  
 
NOAA NATIONAL WEATHER SERVICE - NORTHWEST RIVER FORECAST CENTER  
WWW.NWRFC.NOAA.GOV/SNOW/  
 
USDA NATURAL RESOURCES CONSERVATION SERVICE  
WWW.NRCS.USDA.GOV/WPS/PORTAL/NRCS/MAIN/OR/SNOW/  
 
____________________________________________________________________  
PRECIPITATION AND TEMPERATURE OUTLOOK  
 
THE CLIMATE PREDICTION CENTER PRODUCES MONTHLY AND SEASONAL  
OUTLOOKS, IN WHICH THERE IS A WEIGHING OF THE ODDS OF NEAR-NORMAL,  
ABOVE-NORMAL, OR BELOW-NORMAL TEMPERATURES AND PRECIPITATION.  
 
LOOKING AT THE REMAINDER OF APRIL, THE TREND FOR THE NEXT TWO WEEKS  
LEANS TOWARD BELOW-AVERAGE PRECIPITATION AND ABOVE-AVERAGE  
TEMPERATURES. THIS OUTLOOK TREND ALSO SHOWS UP IN THE OUTLOOK FOR  
THE LAST WEEK OF APRIL.  
 
THE APRIL THROUGH JUNE SEASONAL OUTLOOK SHOWS AN ENHANCED LIKELIHOOD  
OF BELOW-AVERAGE PRECIPITATION AND ABOVE-AVERAGE TEMPERATURES,  
PRIMARILY FOR THE SOUTHERN HALF OF OREGON.  
 
THE JULY THROUGH SEPTEMBER OUTLOOK SHOWS AN ENHANCED LIKELIHOOD OF  
ABOVE AVERAGE TEMPERATURES, WHICH WOULD CAUSE INCREASED VEGETATION  
STRESS, WARMER STREAM TEMPERATURES, AND INCREASED DEMAND FOR  
IRRIGATION WATER.  
 
VISIT WWW.CPC.NCEP.NOAA.GOV FOR MORE ABOUT MONTHLY AND SEASONAL  
OUTLOOKS.  
 
____________________________________________________________________  
RESERVOIRS  
 
RESERVOIR STORAGE AS OF EARLY APRIL IS BELOW TYPICAL CONDITIONS FOR  
THIS TIME OF YEAR, ESPECIALLY FOR SOUTHWEST, SOUTH-CENTRAL, CENTRAL,  
AND PORTIONS OF SOUTHEAST OREGON. THESE ARE REGIONS OF THE STATE  
DEALING WITH DROUGHT IMPACTS FROM THE 2020 WATER YEAR AND LOW  
SNOWPACK AND STREAMFLOW FOR THE CURRENT WATER YEAR. CARRY-OVER  
STORAGE IN THE FALL OF 2020 FOR MANY OF THESE RESERVOIRS WAS MUCH  
LOWER THAN AVERAGE. CONCERNS ARE INCREASING THAT THESE RESERVOIRS  
WILL NOT FILL TO MEET SPRING AND SUMMER IRRIGATION DEMANDS.  
 
OWYHEE RESERVOIR, THE LARGEST IRRIGATION PROJECT IN THE STATE, HAS  
STORAGE OF ABOUT 428,000 ACRE-FEET, 60 PERCENT OF CAPACITY, AS OF  
EARLY APRIL. THIS IS BELOW THE AVERAGE STORAGE FOR THIS TIME OF  
YEAR, AND THE RATE OF INCREASE IS LOWER THAN WHAT IS TYPICALLY SEEN  
IN MARCH AND APRIL. SPRING PRECIPITATION AND SNOWMELT WILL BE  
CRITICAL FOR INFLOW AND STORAGE FOR THIS AND OTHER RESERVOIRS IN THE  
REGION.  
 
RESERVOIR DATA IS PROVIDED BY THE NATURAL RESOURCES CONSERVATION  
SERVICE, THE BUREAU OF RECLAMATION, AND THE US ARMY CORPS OF  
ENGINEERS.  
 
ADDITIONAL RESERVOIR INFORMATION:  
 
WWW.NWD-WC.USACE.ARMY.MIL/NWP/TEACUP/WILLAMETTE/  
WWW.USBR.GOV/PN/HYDROMET/SELECT.HTML  
WWW.WCC.NRCS.USDA.GOV/BASIN.HTML  
 
____________________________________________________________________  
OBSERVED STREAMFLOW  
 
OBSERVED RUNOFF SO FAR THIS WATER YEAR HAS BEEN NEAR AVERAGE FOR  
NORTHWEST AND FAR-NORTHEAST OREGON AND BELOW AVERAGE FOR THE REST OF  
THE STATE. STREAMFLOW IN MARCH WAS BELOW AVERAGE FOR ALL OF OREGON,  
EXCEPT FOR A FEW CREEKS AND RIVERS IN FAR-NORTHEAST OREGON.  
 
VISIT WATERWATCH.USGS.GOV FOR DETAILS ON OBSERVED STREAMFLOW. WATER  
YEAR AND MONTHLY RUNOFF DATA IS AVAILABLE FOR SEVERAL OREGON  
LOCATIONS AT WWW.NWRFC.NOAA.GOV/NATURAL/INDEX.HTML.  
 
____________________________________________________________________  
WATER SUPPLY SEASONAL FORECASTS  
 
WATER SUPPLY FORECASTS FOR APRIL-SEPTEMBER RUNOFF VOLUME ARE BELOW  
AVERAGE FOR MOST OF OREGON, ESPECIALLY CENTRAL AND SOUTH-CENTRAL  
OREGON. THE ONLY WATERSHEDS WITH NORMAL OR ABOVE-NORMAL WATER SUPPLY  
FORECASTS ARE IN NORTH-CENTRAL AND NORTHEAST OREGON. WITH GENERALLY  
DRY CONDITIONS SINCE EARLY MARCH, MOST WATER SUPPLY FORECASTS HAVE  
DECREASED SIGNIFICANTLY.  
 
THE FORECAST FOR THE COLUMBIA RIVER AT THE DALLES, WHICH IS A GOOD  
INDEX OF CONDITIONS ACROSS THE COLUMBIA BASIN, IS 90 PERCENT OF  
AVERAGE FOR APRIL-SEPTEMBER, A DECREASE OF 5 PERCENT FROM A MONTH  
AGO.  
 
DETAILS ON BASIN-SCALE WATER SUPPLY FORECASTS:  
 
NOAA NATIONAL WEATHER SERVICE - NORTHWEST RIVER FORECAST CENTER  
WWW.NWRFC.NOAA.GOV/WS/  
 
USDA NATURAL RESOURCES CONSERVATION SERVICE  
WWW.WCC.NRCS.USDA.GOV/WSF/  
 
____________________________________________________________________  
SPRING FLOOD POTENTIAL  
 
THE RISK OF SPRING SNOWMELT FLOODING IS SLIGHTLY ENHANCED FOR SOME  
WATERSHEDS IN FAR-NORTHEAST OREGON. THAT SAID, THE THREAT OF  
SNOWMELT FLOODING HAS DECREASED SOMEWHAT FROM A MONTH AGO DUE TO  
RELATIVELY DRY CONDITIONS IN MARCH. SPRING FLOODING IS HIGHLY  
DEPENDENT ON TEMPERATURES AND RAINFALL, ALONG WITH SNOWMELT, SO STAY  
TUNED TO WEATHER AND RIVER FORECASTS THROUGH THE SPRING.  
 
FOR MORE INFORMATION ABOUT SPRING FLOOD POTENTIAL AND PEAK FLOW  
FORECASTS, VISIT:  
 
AHPS REGIONAL LONG-RANGE OUTLOOK  
WATER.WEATHER.GOV/AHPS/REGION_LONG_RANGE.PHP?STATE=OR&PERCENT=25  
 
NORTHWEST RIVER FORECAST CENTER PEAK FLOW FORECASTS  
WWW.NWRFC.NOAA.GOV/PEAK/  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab OR Page
The Nexlab WA Page Main Text Page