FGUS76 KPQR 072146 ESFPQR Water Supply Outlook National Weather Service Portland OR 145 PM PST Thursday March 7 2024 ...OREGON WATER SUPPLY SUMMARY AND SPRING FLOOD OUTLOOK AS OF MARCH 7TH 2024... The water supply forecast for the spring and summer of 2024 is near to slightly-above average for most watersheds in Oregon. The primary exception is below average forecasts for several watersheds in south- central Oregon. Seasonal water supply forecasts generally increased 5 to 20 percent from early February. Water supply forecasts may evolve significantly through March and April. The potential for spring snowmelt flooding is low, generally 5 to 25 percent, for watersheds east of the Cascades. Recent increases in snowpack have increased flooding chances slightly, but some watersheds still have multi-year soil moisture and precipitation deficits. Spring snowmelt flooding has historically not occurred along rivers west of the Cascades and is not expected this year. Precipitation so far this water year (Oct 2023 - Feb 2024) is variable statewide, with above average precipitation for coastal portions of western Oregon and most of eastern Oregon, below average for most of the Oregon Cascades, south-central Oregon, and far- northeast Oregon, and near average elsewhere. Refer to the sections below and links provided for details regarding snowpack, precipitation, seasonal climate outlooks, reservoirs, streamflow, and water supply forecasts. The next update to this outlook will be issued by April 3 2024. PRECIPITATION AND TEMPERATURES ACROSS OREGON Precipitation for the 2024 water year thus far (Oct 2023 - Jan 2024) ranges from 75 to 120 percent of average in Oregon, with the lowest percent of average in south-central and interior southwest Oregon and the highest in coastal southwest Oregon and portions of eastern Oregon. February precipitation was above average for most of the state, ranging from 85 to 150 percent of average. Coastal southwest Oregon and most of central and eastern Oregon were above average. Portions of interior southwest Oregon and north-central Oregon were below normal. All remaining areas were near normal. Winter temperatures were above average for all of Oregon, except the Columbia basin portion of north-central Oregon. February temperatures were generally above average statewide and notably much above average for the mountains of northeast Oregon. 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 Westwide Drought Tracker Precipitation & Temperature graphics wrcc.dri.edu/wwdt/index.php?region=or SNOWPACK ACROSS OREGON As of March 5, mountain snowpack was above average for most of Oregon, with basin snowpack ranging from 85 to 130 percent of average. The highest totals relative to average are in the north Oregon Coast Range and the mountains of east-central Oregon. Snowpack in the Cascades is generally a little above average, ranging from 90 to 120 percent of average. Basin totals for the Cascades range from 70 to 85 percent. In recent weeks, snowpack increased gradually from mid February onward and more sharply in late February and early March. Additional mountain snow is forecast through mid March. Seasonally, significant snow accumulation is possible through March for southern Oregon and April for northern Oregon. Additional snowpack information: NOAA National Weather Service - Northwest River Forecast Center www.nwrfc.noaa.gov/snow/ USDA Natural Resources Conservation Service nwcc-apps.sc.egov.usda.gov/imap/ 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. Strong El Nino conditions in the tropical Pacific have been the driving factor for seasonal outlooks through the winter, but El Nino conditions are expected to moderate through the spring and early summer. Historically, the primary impact of El Nino on Oregon conditions is above-average temperatures. Based on the continued influence of El Nino and long-term temperature trends, the outlook for March through May is for an enhanced likelihood of above-average temperatures. The precipitation outlook also indicates a slightly-enhanced likelihood for below- average precipitation, albeit less confident than the temperature outlook. The outlook for the likelihood of above-average temperatures and below-average precipitation continues through the summer. Visit www.cpc.ncep.noaa.gov for more about seasonal outlooks. RESERVOIRS Reservoir storage for most irrigation reservoirs across the state is generally above average, with the exception of southwest Oregon. Reservoir storage ranges from about 50 to 90 percent of capacity, much of that being carry-over storage from last year. Flood control reservoirs are dependent on spring precipitation and snowmelt to refill March through May. Owyhee Reservoir, the largest irrigation project in the state, has observed storage of about 536,000 acre-feet, an increase of 77,000 acre-feet from a month ago. This is 75 percent of capacity and 133 percent of average for this time of 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.nwd-wc.usace.army.mil/nwp/teacup/willamette/ www.usbr.gov/pn/hydromet/select.html www.wcc.nrcs.usda.gov/basin.html OBSERVED STREAMFLOW Observed runoff so far this water year has been above average for most watersheds statewide, particularly so for watersheds in central Oregon. The only area with below-average runoff is south-central and interior southwest Oregon. Runoff in February was generally near to above average statewide, again with the exception of below average for watersheds in the Klamath basin. Visit waterwatch.usgs.gov for details on observed streamflow. Runoff data is available at www.nwrfc.noaa.gov/natural/index.html at water year and monthly time scales for several locations in Oregon. WATER SUPPLY SEASONAL FORECASTS Water supply forecasts for April-September runoff volume are near to above average for most of the state, except for below-average forecasts for watersheds within the Klamath basin. The highest forecasts, relative to average, are in central and east-central Oregon. Forecasts for the April-September period may change significantly through March and April. The forecast for the Columbia River at The Dalles, which is a good index of conditions across the Columbia Basin, is 82 percent of average for April-September. Details on basin-scale water supply forecasts: NOAA NWS - Northwest River Forecast Center www.nwrfc.noaa.gov/ws/ NOAA NWS - California-Nevada RFC (Klamath basin) www.cnrfc.noaa.gov/water_resources_update.php USDA Natural Resources Conservation Service www.wcc.nrcs.usda.gov/wsf/ $$