FGUS76 KPQR 032301 ESFPQR Water Supply Outlook National Weather Service Portland OR 400 PM PST Wednesday April 3 2024 ...OREGON WATER SUPPLY SUMMARY AND SPRING FLOOD OUTLOOK AS OF APRIL 3RD 2024... The water supply forecast for the spring and summer of 2024 is near average for watersheds in the Cascades and most of northeast Oregon, below average for the Klamath basin and most of western Oregon, and above average for some watersheds in east-central and southeast Oregon. Forecasts declined 10 to 20 percent for most watersheds in western Oregon and the Klamath basin. There was a mix of increases and decreases for forecasts for much of central and eastern Oregon. Water supply forecasts may evolve significantly through April. The potential for spring snowmelt flooding is low, generally 10 to 30 percent, for watersheds in central and northeast Oregon. Any flooding that occurs would likely be caused by either a period of much-above average temperatures or a combination of above-average temperatures and moderate to heavy precipitation. 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 - Mar 2024) is near average for most of the state but above average for coastal portions of southwest and southeast Oregon. Temperatures for the water year thus far are above average and notably so portions of northeast and south-central Oregon. 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 May 6, 2024. PRECIPITATION AND TEMPERATURES ACROSS OREGON Precipitation for the 2024 water year thus far (Oct 2023 - Mar 2024) ranges from 75 to 115 percent of average in Oregon, but most portions of the state are near average, 90 to 110 percent. The lowest values are in far-northeast Oregon and the Klamath basin, and the highest are in southeast Oregon. March precipitation was above average for most of the southern half of Oregon and coastal portions of northwest Oregon and below average for most of the northern half of Oregon. Temperatures for October through March were 1 to 4 degrees above average for almost all of Oregon, except near normal for the Columbia basin portion of north-central Oregon. March temperatures were 1 to 4 degrees below normal for the southern half of the state and near average for the northern half of the state. 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 April 1, mountain snowpack was above average for most of Oregon, with basin snowpack ranging from 85 to 125 percent of average. The highest totals relative to average are across the southern third of the state, and the lowest totals in far-northeast Oregon. Snowpack in the Cascades is generally above average north and below average south. Snowpack increased notably in the first half of March, with significant snowmelt in late March. Additional mountain snow is possible through April, but the snowmelt season that began in late March has continued in early April and is likely continue through April, with brief interruptions due to cooler temperatures and mountain snow. Oregon snowpack typically melts out between early May and early June. 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. El Nino conditions are moderate through the spring and expected to be transition to ENSO neutral by early summer and are likely to transition to La Nina by autumn 2024. ENSO conditions have a minimal impact on summer conditions but will likely have a strong influence on the upcoming fall and winter. The outlook for April through June is for an enhanced likelihood of above-average temperatures. The precipitation outlook also indicates a slightly-enhanced likelihood for below-average precipitation for northwest Oregon, with equal chances of near, above, or below average elsewhere. 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 100 percent of capacity. Notably, most reservoirs in central and eastern Oregon have filled to capacity. Flood control reservoirs in western Oregon are dependent on spring precipitation and snowmelt to refill March through May, and most are currently refilling a little behind the rule curve schedules. Owyhee Reservoir, the largest irrigation project in the state, has observed storage of about 660,000 acre-feet, an increase of 124,000 acre-feet from a month ago. This is 92 percent of capacity and 131 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 and southwest Oregon. The only area with below-average runoff is south-central and interior southwest Oregon. Runoff in March was generally near to above average statewide, but above average for coastal portions of western Oregon and 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 in west-central and northwest Oregon and within the Klamath basin in south-central Oregon. The highest forecasts, relative to average, are in central and east-central Oregon. The forecast for the Columbia River at The Dalles, which is a good index of conditions across the Columbia Basin, is 81 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/ $$