Hydrologic Outlook
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000 FGUS76 KPQR 061713 ESFPQR Water Supply Outlook National Weather Service Portland OR 915 AM PST Wednesday March 6 2019 ...OREGON WATER SUPPLY AND SPRING FLOOD POTENTIAL OUTLOOK AS OF MARCH 6TH 2019... The water supply forecast for the spring and summer of 2019 is near- average for most Oregon watersheds. Exceptions are some above- average forecasts in central and northeast Oregon and some below- average forecasts in northwest and far-southeast Oregon. Cold temperatures and ample snowfall in February resulted in increases in all water supply forecast volumes in Oregon compared to a month ago. The increased snowpack also raises concerns somewhat about the potential for spring flooding in central and eastern Oregon, although the threat of snowmelt-related flooding remains low. The March 2019 outlook by the Climate Prediction Center calls for enhanced likelihood of below-average temperatures statewide, especially for the first half of the month. For precipitation, there is enhanced likelihood of above-average in southern Oregon, with equal chances of near, below, or above-average precipitation for northern Oregon. 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. Most of Oregon has been affected by drought for the past year, with very low streamflow seen statewide since summer 2018. Drought conditions remain but have improved significantly since late January. For information about drought declarations and impacts around the state, visit the Oregon Water Resources Department drought page at www.oregon.gov/owrd/pages/wr.drought.gov. The next update will be issued by April 5, 2019. ============================================================ Precipitation and Temperatures across Oregon Precipitation for the 2019 water year thus far (Oct 1, 2018 through March 4, 2019) ranges from 75 to 100 percent of average in Oregon, highest in northeast and southwest Oregon and lowest in northwest Oregon. Precipitation during February was 150 to 200 percent of average for most of the state, with the exception of 120 to 150 percent of average in northwest Oregon. Temperatures this winter prior to February were predominantly above- average, but there was an abrupt change in February, with temperatures across Oregon 5 to 8 degrees below average and relatively low freezing levels through the month. 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 March, basin snowpack ranges from 90 to 150 percent of average, in terms of the water content of the snow. This is a major increase from late January, when basin snowpack ranged from 50 to 105 percent of average. Snow-water content relative to average is lowest for northwest Oregon, especially in the north Cascades near Mt. Hood and Mt. Jefferson, and highest in the Blue and Wallowa Mountains of eastern Oregon. Weather conditions November through January were not favorable for building snowpack, with above-average temperatures and below-average precipitation. However, February was an abrupt change to cold and wet conditions, changing the snowpack condition from below to above average in just a few weeks. 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. The March outlook from the Climate Prediction Center calls for enhanced likelihood of below-average temperatures statewide, especially for the first half of the month. The outlook for precipitation indicates an enhanced likelihood of above-average precipitation in southern Oregon, with equal chances of near, below, or above-average precipitation for northern Oregon. The outlook for April through June calls for enhanced likelihood of above-average temperatures, with equal chances of near, above, or below-average precipitation statewide. Visit www.cpc.ncep.noaa.gov for more about seasonal outlooks. =================================================================== Reservoirs Reservoir storage as of early March is below average, generally 30 to 80 percent of average for this time of year and 20 to 80 percent of capacity. The major increases in mountain snowpack statewide during February have improved prospects for at least some irrigation reservoirs to fill later this spring. For Corps of Engineers reservoirs in the Willamette basin, the refill season started in early February. Most Willamette projects are filling slower than the refill curve. Spring precipitation will have a big impact on them filling by the end of May. 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 so far this water year is below-average, generally 45 to 80 percent in terms of runoff volume October 2018 through February 2019. The lowest values relative to normal are in northwest Oregon and portions of southeast Oregon. The below-average runoff so far this water year is caused by overall below-average precipitation along with a lack of heavy-precipitation events causing major rises on rivers during the winter. Looking more recently at the past four weeks, streamflow was near- average for rivers draining lower-elevation areas and below-average for rivers draining higher-elevation areas, where most of the precipitation in February fell as snow and didn`t produce much runoff. 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 Water supply forecasts for April-September runoff volume range from about 65 to 110 percent of average in western Oregon and far southeast Oregon and 100 to 140 percent of average in central and eastern Oregon, highest in far-northeast Oregon. These forecasts represent a major increase from a month ago, anywhere from 10 to 40 percent of average, due to the above-average precipitation and major increases in mountain snowpack in February. The forecast for the Columbia River at The Dalles, which is a good index of conditions across the Columbia Basin, is 87 percent of average for April-September, reflecting near to below-average snowpack across much of the Columbia basin. This forecast value is unchanged from a month ago and is 23 percent lower than this same time last year. 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 potential for flooding along rivers in central and eastern Oregon is low despite the recent increases in mountain snowpack. In northeast Oregon (Blue and Wallowa Mountains), there is a slightly elevated risk of spring flooding due to higher than normal snowpack as of early March. Accumulated snow at lower elevations in northeast Oregon also adds to the slightly elevated risk. However, there is no indication of an imminent rapid warm-up or heavy precipitation that would result in flooding. This is something to monitor through the spring. Historically, the frequency of spring flooding east of the Cascades is low, but when it does occur, it typically involves a combination of snowmelt and rainfall runoff. Snowmelt-driven spring flooding doesn`t occur in western Oregon. Stay tuned to snowpack conditions and streamflow forecasts at www.nwrfc.noaa.gov. Bryant $$

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