Flood Potential Outlook
Issued by NWS Portland, OR

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WATER SUPPLY OUTLOOK
NATIONAL WEATHER SERVICE PORTLAND OR
150 PM PDT THURSDAY MAY 07 2015

...OREGON WATER SUPPLY OUTLOOK AS OF MAY 7 2015...

THE OREGON WATER SUPPLY FOR THE SPRING AND SUMMER IS FORECAST TO BE
BELOW-NORMAL FOR OREGON. WITH BELOW-NORMAL PRECIPITATION IN
APRIL...WATER SUPPLY FORECAST DROPPED SIGNIFICANTLY FOR MOST RIVER
BASINS. FORECASTS FOR BASINS EAST OF THE CASCADES RANGE FROM 10 TO
50 PERCENT OF AVERAGE FOR SEASONAL STREAMFLOW VOLUMES. FORECASTS FOR
BASINS WEST OF THE CASCADES RANGE FROM 30 TO 60 PERCENT OF AVERAGE.
WATER SUPPLY FORECASTS ARE BASED ON CURRENT SNOWPACK CONDITIONS AND
OBSERVED PRECIPITATION THUS FAR THIS WINTER. IT IS UNLIKELY THAT
PRECIPITATION TOTALS IN MAY AND JUNE WILL HAVE A SUBSTANTIAL IMPACT
ON WATER SUPPLY FORECASTS.

THE BIG STORY THIS WINTER IS THE LACK OF SNOWPACK IN OREGON
MOUNTAINS...ESPECIALLY THE CASCADES. MANY NRCS SNOTEL STATIONS
REMAINED SNOW-FREE THROUGH APRIL...A MONTH THAT TYPICALLY HAS THE
PEAK SEASONAL SNOWPACK FOR MOST STATIONS. THE LOW SNOWPACK IS DUE
PRIMARILY TO ABNORMALLY WARM TEMPERATURES...ALTHOUGH PRECIPITATION
HAS BEEN BELOW AVERAGE FOR A LOT OF THE STATE SINCE JANUARY.
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 SUMMER...CONTINUING THE TREND OF
ABOVE-NORMAL TEMPERATURES FOR THE PAST SEVERAL MONTHS. FOR
PRECIPITATION...THE SUMMER OUTLOOK INDICATES EQUAL CHANCES OF
NORMAL...BELOW-NORMAL...OR ABOVE-NORMAL PRECIPITATION FOR OREGON.
HOWEVER...SUMMER IS THE DRY TIME FOR MOST OF OREGON...AND
PRECIPITATION TOTALS WILL NOT INCREASE WATER YEAR TOTALS
SIGNIFICANTLY. 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: BAKER...CROOK...HARNEY...KLAMATH...LAKE...MALHEUR
AND WHEELER. 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 AND
WWW.OREGON.GOV/OWRD/PAGES/WR/DROUGHT.ASPX.

THE NEXT UPDATE OF THIS OUTLOOK WILL BE ISSUED BY JUNE 10TH.

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

SNOWPACK AS OF EARLY MAY REMAINS VERY LOW...MUCH BELOW-NORMAL IN ALL
BASINS. APRIL IS TYPICALLY THE TIME OF YEAR OF PEAK SEASONAL
SNOWPACK BEFORE SPRING MELT BEGINS...BUT THIS YEAR MANY SNOTEL
STATIONS HAVE HAD ZERO SNOW-WATER EQUIVALENT FOR THE PAST SEVERAL
WEEKS. MANY CURRENT VALUES ARE BELOW PREVIOUS RECORD LOWS. SNOW
ACCUMULATION IN THE CASCADES OR EASTERN OREGON MOUNTAINS IS UNLIKELY
IN MAY AS WE MOVE INTO THE SUMMER MONTHS.

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 65 TO 85 PERCENT FOR THE
FIRST SIX MONTHS OF THE 2015 WATER YEAR. APRIL PRECIPITATION WAS
BELOW-AVERAGE...GENERALLY 40 TO 70 PERCENT...DRIVING SEASONAL TOTALS
FURTHER BELOW-AVERAGE.

WARM TEMPERATURES HAVE HAD A BIG IMPACT ON SNOWPACK THIS WINTER...
WITH MONTHLY TEMPERATURES AS HIGH AS 10 DEGREES ABOVE AVERAGE FOR
THE PAST FEW MONTHS. HOWEVER...APRIL TEMPERATURES WERE ACTUALLY NEAR-
AVERAGE BUT STILL TOO WARM FOR SIGNIFICANT SNOW ACCUMULATION 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

NOAA`S NATIONAL WEATHER SERVICE - CALIFORNIA NEVADA RFC
(KLAMATH BASIN ONLY) WWW.CNRFC.NOAA.GOV/WATER_RESOURCES_UPDATE.PHP

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

RESERVOIR STORAGE REMAINS WELL BELOW CAPACITY...GENERALLY 25 TO 75
PERCENT OF CAPACITY IN EASTERN OREGON...60 TO 90 PERCENT FOR CENTRAL
OREGON...AND 40 TO 70 PERCENT IN WESTERN OREGON. WITH THE LOW
SNOWPACK AND BELOW-NORMAL SPRING RAINFALL...RESERVOIR INFLOW WILL
PROBABLY BE LOWER THAN TYPICAL FOR MAY. OF PARTICULAR NOTE...OWYHEE
RESERVOIR...THE LARGEST IRRIGATION RESERVOIR IN OREGON...ONLY HAS
180 THOUSAND ACRE FEET...25 PERCENT OF CAPACITY. MOST CORPS OF
ENGINEERS RESERVOIRS IN THE WILLAMETTE VALLEY AND SOUTHWEST OREGON
ARE TRACKING WELL BELOW THE SPRING REFILL SCHEDULE AND WILL NOT 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 APRIL WAS BELOW-AVERAGE FOR OREGON RIVERS.
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 10 TO 60 PERCENT OF AVERAGE FOR
OREGON BASINS AND ARE LOWEST IN SOUTHEAST OREGON. FORECASTS FOR MOST
BASINS HAVE DECLINED 10 TO 20 PERCENT OVER THE PAST MONTH DUE TO THE
LACK OF PRECIPITATION IN APRIL.

THE FORECAST FOR THE COLUMBIA RIVER AT THE DALLES...WHICH IS A GOOD
INDEX OF CONDITIONS ACROSS THE COLUMBIA BASIN...IS 72% OF AVERAGE
FOR THE APRIL-SEPTEMBER PERIOD...A DECLINE OF 11% FROM A MONTH AGO.

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/

BRYANT
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