Flood Potential Outlook
Issued by NWS Portland, OR

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WATER SUPPLY OUTLOOK
NATIONAL WEATHER SERVICE PORTLAND OR
420 PM PDT TUE APR 07 2015

...OREGON WATER SUPPLY AND SPRING FLOOD POTENTIAL OUTLOOK AS OF
APRIL 7 2015...

THE OREGON WATER SUPPLY FOR THE COMING SPRING AND SUMMER IS FORECAST
TO BE BELOW-NORMAL FOR OREGON...ESPECIALLY FOR BASINS EAST OF THE
CASCADES...WHERE WATER SUPPLY FORECASTS RANGE FROM 20 TO 70 PERCENT
OF AVERAGE FOR APRIL-SEPTEMBER RUNOFF PERIOD. FORECASTS FOR BASINS
WEST OF THE CASCADES RANGE FROM 50 TO 80 PERCENT OF AVERAGE. WATER
SUPPLY FORECASTS ARE BASED ON CURRENT SNOWPACK CONDITIONS AND
OBSERVED PRECIPITATION THUS FAR THIS WINTER. SIGNIFICANT
PRECIPITATION AND SNOW ACCUMULATION TYPICALLY OCCURS THROUGH THE
SPRING...AND CHANGES IN THE WATER SUPPLY FORECASTS ARE POSSIBLE
DURING THE NEXT COUPLE MONTHS.

THE POTENTIAL FOR SPRING SNOWMELT FLOODING IN OREGON IS BELOW-
AVERAGE DUE TO THE VERY LOW SNOWPACK AND THE SPRING OUTLOOK FOR
CONTINUED ABOVE-NORMAL TEMPERATURES. SPRINGTIME /MAY-JUNE/ FLOODING
IS TYPICALLY LIMITED TO BASINS EAST OF THE CASCADES AND IS USUALLY
CAUSED BY A COMBINATION OF RAINFALL AND SNOWMELT.

THE BIG STORY THIS WINTER IS THE LACK OF SNOWPACK IN OREGON
MOUNTAINS...ESPECIALLY THE CASCADES. SEVERAL NRCS SNOTEL STATIONS IN
THE CASCADES AND OTHER OREGON MOUNTAIN RANGES SHOW LITTLE OR NO
SNOW...WITH CURRENT VALUES AT MANY STATIONS BELOW PREVIOUS RECORD
LOWS. THE LOW SNOWPACK IS DUE PRIMARILY TO ABNORMALLY WARM
TEMPERATURES...ALTHOUGH PRECIPITATION HAS BEEN BELOW AVERAGE FOR A
LOT OF THE STATE SINCE JANUARY. IF THE LACK OF SNOWPACK CONTINUES
THROUGH THE SPRING...POSSIBLE IMPLICATIONS INCLUDE BELOW-NORMAL
SUMMER STREAMFLOW AND ABOVE-NORMAL WATER TEMPERATURES.

REFER TO THE SECTIONS BELOW AND THE LINKS PROVIDED FOR DETAILS
REGARDING SNOWPACK...PRECIPITATION...RESERVOIR CONDITIONS AND WATER
SUPPLY FORECASTS FOR INDIVIDUAL BASINS.

NOAA`S CLIMATE OUTLOOKS INDICATES THAT ABOVE-NORMAL TEMPERATURES ARE
LIKELY TO CONTINUE THROUGH THE SPRING...CONTINUING THE TREND OF
RELATIVELY WARM TEMPERATURES. FOR PRECIPITATION...THE SPRING OUTLOOK
LEANS BELOW-NORMAL FOR WESTERN OREGON...WITH EQUAL CHANCES OF
NORMAL...BELOW-NORMAL...OR ABOVE-NORMAL PRECIPITATION FOR EASTERN
OREGON. FOR MORE INFORMATION ON SEASONAL OUTLOOKS AND EL NINO
CONDITIONS...VISIT THE CLIMATE PREDICTION CENTER WEB PAGE AT
WWW.CPC.NCEP.NOAA.GOV.

SEVERAL COUNTIES IN CENTRAL AND SOUTHERN OREGON ALREADY HAVE ONGOING
DROUGHT ISSUES DUE TO DRY CONDITIONS DURING THE PAST COUPLE YEARS.
STATE DROUGHT DECLARATIONS ARE NOW IN EFFECT FOR THE FOLLOWING
OREGON COUNTIES: KLAMATH...CROOK...LAKE...HARNEY...AND MALHEUR.
DROUGHT CONDITIONS ARE LIKELY TO PERSIST OR WORSEN FOR MUCH OF THE
STATE BASED ON WHAT HAS HAPPENED THUS FAR THIS WATER YEAR. FOR THE
LATEST DROUGHT INFORMATION...VISIT DROUGHT.GOV.

THE NEXT UPDATE OF THIS OUTLOOK WILL BE ISSUED BY MAY 8TH.

============================================================
SNOWPACK ACROSS OREGON

SNOWPACK AS OF EARLY APRIL REMAINS VERY LOW...MUCH BELOW-NORMAL IN
ALL BASINS. THIS IS THE TIME OF YEAR THAT IS TYPICALLY THE PEAK
SNOWPACK FOR THE SEASON...BUT THIS YEAR MANY SNOTEL STATIONS ARE
REPORTING ZERO SNOW-WATER EQUIVALENT...AND MANY CURRENT VALUES ARE
BELOW PREVIOUS RECORD LOWS. THE BASIN PERCENT OF NORMAL FOR BOTH THE
WEST AND EAST SLOPES OF THE CASCADES IS ABOUT 10 PERCENT. FOR
EASTERN OREGON...THE PICTURE IS MORE VARIABLE BUT STILL VERY
LOW...RANGING FROM 5 TO 35 PERCENT OF AVERAGE. SNOWPACK VALUES HAVE
BEEN ON THE DECLINE FOR ALL LOCATIONS SINCE EARLY JANUARY WITH MANY
DAYS OF RELATIVELY WARM AND DRY CONDITIONS MIXED WITH A FEW PERIODS
OF RAIN. ALTHOUGH SEVERAL SNOTEL STATIONS HAVE HAD MINOR INCREASES
IN SNOW-WATER EQUIVALENT DURING THE FIRST WEEK OF APRIL...MAJOR
INCREASES THROUGH THE REMAINDER OF SPRING ARE UNLIKELY...AS THE
TEMPERATURE OUTLOOK FROM THE CLIMATE PREDICTION CENTER INDICATES
ABOVE-NORMAL TEMPERATURES ARE LIKELY TO CONTINUE.

REFER TO THE FOLLOWING LINKS FOR MORE DETAILS.

NOAA`S 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 TEMPERATURES ACROSS OREGON

SEASONAL PRECIPITATION TOTALS RANGE FROM 70 TO 90 PERCENT FOR THE
FIRST SIX MONTHS OF THE 2015 WATER YEAR. MARCH PRECIPITATION WAS
NEAR AVERAGE FOR NORTHWEST OREGON BUT BELOW AVERAGE EVERYWHERE ELSE
IN THE STATE.

WARM TEMPERATURES HAVE BEEN THE BIG CLIMATE STORY OF THE WINTER.
MONTHLY TEMPERATURES IN MARCH WERE SEVERAL DEGREES ABOVE AVERAGE...
CONTINUING THE TREND SINCE THE FIRST OF THE YEAR. THE ABOVE-AVERAGE
TEMPERATURES HAVE BEEN ESPECIALLY NOTABLE IN THE CASCADES AND
EASTERN OREGON MOUNTAINS.

VISIT THE FOLLOWING LINK FOR MORE DETAILS ON PRECIPITATION AND
TEMPERATURES.

NOAA`S NATIONAL WEATHER SERVICE - NORTHWEST RIVER FORECAST CENTER
WWW.NWRFC.NOAA.GOV/WATER_SUPPLY/WY_SUMMARY/WY_SUMMARY.PHP

============================================================
MAJOR IRRIGATION RESERVOIRS

RESERVOIR STORAGE REMAINS WELL BELOW CAPACITY...GENERALLY 20 TO 80
PERCENT OF CAPACITY. WITH THE LACK OF SNOWPACK...RESERVOIR INFLOW
WILL BE HIGHLY DEPENDENT ON SPRING RAINFALL AND IS LIKELY TO REMAIN
WELL BELOW CAPACITY. OF PARTICULAR NOTE...OWYHEE RESERVOIR...THE
LARGEST IRRIGATION RESERVOIR IN OREGON...ONLY HAS 190 THOUSAND ACRE
FEET...27 PERCENT OF CAPACITY. MOST CORPS OF ENGINEERS RESERVOIRS IN
THE WILLAMETTE VALLEY AND SOUTHWEST OREGON ARE TRACKING WELL BELOW
THE SPRING REFILL SCHEDULE...AND IT IS VERY QUESTIONABLE IF THEY
WILL FILL TO SUMMER FULL POOL LEVELS.

RESERVOIR DATA IS PROVIDED BY THE NATURAL RESOURCES CONSERVATION
SERVICE...THE BUREAU OF RECLAMATION...AHD THE US ARMY CORPS OF
ENGINEERS.

VISIT THE FOLLOWING LINKS FOR MORE RESERVOIR INFORMATION:
WWW.WCC.NRCS.USDA.GOV/BASIN.HTML
WWW.USBR.GOV/PN/HYDROMET/SELECT.HTML WWW.NWD-
WC.USACE.ARMY.MIL/NWP/TEACUP/WILLAMETTE/

============================================================
CURRENT AND FORECAST STREAMFLOW

OBSERVED STREAMFLOW FOR MARCH WAS BELOW-NORMAL FOR MOST OREGON
BASINS...ESPECIALLY SO FOR WESTERN OREGON. MOST STREAMS HAD NO MAJOR
RISES DURING THE MONTH...AND STREAMFLOW IN MANY BASINS IS TRENDING
DOWN MUCH FASTER THAN USUAL TOWARD SUMMER BASE FLOW DUE TO THE LACK
OF SNOWMELT AND THE LOWER-THAN-AVERAGE PRECIPITATION IN RECENT WEEKS.

VISIT WATERWATCH.USGS.GOV FOR MORE DETAILS ON OBSERVED STREAMFLOW.

FORECAST STREAMFLOW VOLUMES FOR THE SPRING AND SUMMER
/GENERALLY APRIL THROUGH SEPTEMBER/ RANGE FROM 20 TO 50 PERCENT OF
AVERAGE FOR BASINS IN SOUTH-CENTRAL AND SOUTHEAST OREGON...30 TO 75
PERCENT OF AVERAGE FOR NORTHEAST OREGON BASINS...AND 55 TO 75
PERCENT FOR WESTERN OREGON BASINS. FORECASTS FOR MOST BASINS HAVE
DECLINED 10 TO 30 PERCENT OVER THE PAST TWO MONTHS DUE TO THE
PREDOMINANTLY DRY AND WARM CONDITIONS IN FEBRUARY AND MARCH.

THE FORECAST FOR THE COLUMBIA RIVER AT THE DALLES...WHICH IS A GOOD
INDEX OF CONDITIONS ACROSS THE COLUMBIA BASIN...IS 83% OF AVERAGE
FOR THE APRIL-SEPTEMBER PERIOD.

VISIT THE FOLLOWING LINKS FOR MORE DETAILS ON BASIN-SCALE WATER
SUPPLY FORECASTS:

NOAA`S 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 POTENTIAL FOR SPRING SNOWMELT FLOODING IN OREGON IS BELOW-
AVERAGE AND APPEARS HIGHLY UNLIKELY THROUGHOUT OREGON DUE TO THE
VERY LOW SNOWPACK AND THE SPRING OUTLOOK FOR CONTINUED ABOVE-NORMAL
TEMPERATURES. SPRINGTIME /MAY-JUNE/ FLOODING IS TYPICALLY LIMITED TO
BASINS EAST OF THE CASCADES AND IS USUALLY CAUSED BY A COMBINATION
OF RAINFALL AND SNOWMELT.

BRYANT
$$



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