Hydrologic Outlook
Issued by NWS Portland, OR
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057 FGUS76 KPQR 052309 ESFPQR Water Supply Outlook National Weather Service Portland OR 310 PM PST Monday March 5 2018 ...OREGON WATER SUPPLY OUTLOOK AS OF MARCH 5TH 2018... The water supply forecast for the spring and summer of 2018 is below- average for most Oregon watersheds, especially so for the southern half of the state. April through September runoff-volume forecasts range from 20 to 100 percent of average, lowest in south-central Oregon and highest in northwest and far-northeast Oregon. Snowpack is notably low in the Cascades and all mountain ranges in eastern Oregon. After a relatively-dry December and a relatively- warm January, there were several storms that increased snowpack in the latter half of February, moreso for the northern than the southern half of the state. February was also the first month this winter with widespread below-average temperatures in Oregon. The March 2018 outlook by the Climate Prediction Center calls for a enhanced likelihood of below-average temperatures and above-average precipitation in Oregon. Looking at April through June, there are equal chances of near, above, or below-average precipitation and temperatures across the state. For the summer outlook, there is an enhanced possibility of above-average temperatures. For more 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. The next update will be issued by April 4, 2018. ============================================================ Snowpack across Oregon As of early March, basin snowpack ranges from 45 to 80 percent of average, in terms of the water content of the snow. Values are lowest across the southern half of the state. Weather conditions in December and January were generally not favorable for building snowpack. However, February temperatures were below-average statewide and precipitatinotablyon was near or a little below-average. Basin snowpack, in terms of snow-water equivalent percent of average, increased by 10 to 25 percent in February. That said, seasonal totals remain below average, especially in the southern half of the state. 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 March 4, 2018) ranges from 70 to 100 percent of average in Oregon, highest in northwest and far-northeast Oregon and lowest in south- central and southeast Oregon. Temperatures in December and January were above-average, especially at higher elevations. Temperatures in February were 1 to 3 degrees below-average statewide. 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 March is generally average to a little above-average for this time of year and 50 to 90 percent of storage capacity. Many reservoirs around the state have carry-over storage from last year. 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 February 2018 varied greatly, relative to average, around the state. In southwest and south-central Oregon, streamflow was much below average, while in far-northeast Oregon, streamflow was above-average. Elsewhere in the state, streamflow was near or a little below-average. 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 are mostly between 50 and 85 percent of average, with some forecasts in southern Oregon as low as 20 percent of average and some in far-northwest and far- northeast as high as 100 percent. These forecasts are updated daily and have generally been trending upward since mid February, moreso for northern Oregon basins. The forecast for the Columbia River at The Dalles, which is a good index of conditions across the Columbia Basin, is 110 percent of average for April-September, an increase of 3 percent from a month ago. This forecast for The Dalles reflects above-average snowpack in northern Washington and the Rocky Mountain portion of the Columbia River basin. 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, OR 97230-1089
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