Hydrologic Outlook
Issued by NWS Portland, OR
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000 FGUS76 KPQR 051921 ESFPQR Water Supply Outlook National Weather Service Portland OR 1220 PM PDT Tuesday June 5 2018 ...OREGON WATER SUPPLY OUTLOOK AS OF JUNE 5TH 2018... The water supply forecast for the summer of 2018 is below-average for most of Oregon, especially central and southeast, but is near- average for some basins in northwest, far-northeast, and coastal portions of southwest Oregon. April through September runoff-volume forecasts range from as low as 20 percent of average in southeast Oregon to 110 percent of average in northwest Oregon. Seasonal snowpack peaked in March, with rapid melt in April and May. Seasonal snowpack ranged from 40 to 70 percent of average for most of the state but 70 to 90 percent for the north Cascades and far- northeast Oregon mountains. As of early June, snow had almost completely melted from Oregon mountains, other than the volcanic peaks in the Cascades. May 2018 was notably dry and warm for much of Oregon, with precipitation only 10 to 50 percent of average for western and northern Oregon. However, far-southeast Oregon was a little above- average, providing some minor relief from dry conditions earlier in the spring. Temperatures were 3 to 6 degrees above average for central and eastern Oregon and 1 to 3 degrees above average for western Oregon. Expect relatively dry and warm conditions for June and through the summer months. The Climate Prediction Center outlook for June through August highlights the enhanced likelihood of above-average temperatures. For details, visit www.cpc.ncep.noaa.gov. Refer to the sections below and links provided for details regarding snowpack, precipitation, reservoir conditions, and water supply forecasts for individual basins. This will be the final water supply outlook issued for this season. However, NWS Portland will issue monthly Drought Information Statements beginning July 3rd due to ongoing drought conditions for much of Oregon. ============================================================ Snowpack across Oregon Seasonal snowpack peaked in March and was as low as 40 percent of average in southeast Oregon and as high as 90 percent of average in the vicinity of Mt Hood in the Cascades and in the Wallowa Mountains of northeast Oregon. As of early June, snow has completely melted at all but a few SNOTEL stations. Snowmelt began in April and accelerated in May due to above-average 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 Temperatures across Oregon Precipitation for the 2018 water year thus far (Oct 1, 2017 through June 4, 2018) ranges from 70 to 95 percent of average in Oregon, highest in northwest and far-northeast Oregon and lowest in south- central Oregon. Temperatures were notably above-average in May, generally 2 to 6 degrees above average. Portland reported the 2nd driest and warmest May on record. 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 ============================================================ Reservoirs Reservoir storage as of early June was generally a little below average for most reservoirs, resulting from a combination of low seasonal snowpack and unusually high irrigation demand in May due to warm and dry conditions. In the Willamette basin, the USACE flood control reservoirs only filled to about 75 percent of summer full pool storage, with notably low levels at reservoirs in the southern part of the basin. Storage at Owyhee, the largest irrigation reservoir in the state, is 72 percent of capacity and 97 percent of average. 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.wcc.nrcs.usda.gov/basin.html www.usbr.gov/pn/hydromet/select.html www.nwd-wc.usace.army.mil/nwp/teacup/willamette/ ============================================================ Observed Streamflow Observed streamflow in May 2018 was about 60 percent of average statewide, mainly due to the much below-average precipitation in most of the state. Visit waterwatch.usgs.gov for details on observed streamflow. Water year and monthly runoff data is available at www.nwrfc.noaa.gov for several locations in Oregon. ============================================================ Forecast Streamflow and Seasonal Runoff Volumes Forecasts for April-September runoff volume vary widely around the state. Most northwest and far-northeast Oregon basins are between 70 and 115 percent of average. Forecasts for southwest basins range from 50 to 100 percent of average, highest for coastal basins. Forecasts for central and southeast Oregon are the lowest in the state in terms of percent of average, generally ranging from 30 to 60 percent of average but as low as 20 percent. The below-average seasonal runoff is due to the the low mountain snowpack this past winter and dry and warm conditions during the spring. The forecast for the Columbia River at The Dalles, which is a good index of conditions across the Columbia Basin, is 121 percent of average for April-September, an increase of 2 percent from a month ago. This forecast for The Dalles reflects above-average snowpack in northern Washington, the upper Snake basin, and the Rocky Mountain portion of the Columbia River basin in western Montana and British Columbia. 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/ Bryant $$

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Portland Weather Forecast Office
5241 NE 122nd Avenue
Portland, OR 97230-1089
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Page last modified: 5-Jun-2018 7:21 PM
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