Situational Awareness (Friday, 2025-12-19)
According to the Middle Atlantic River Forecast Center, observed precipitation yesterday ranged from about 0.25 to 0.75 inches. Over the next five days, average basin rainfall is expected to be around 0.01 to 0.25 inches, with some areas possibly receiving up to 0.5 inches.
Special Conditions
Point of Rocks flow (USGS site 01638500) was affected by ice at the measurement site from December 15 through December 17, and the gage resumed recording flow on December 17. Temperatures have since been warm enough to support rainfall, and ice effects at USGS gages have stopped.
U.S. Drought Monitor percent coverage of the Potomac for D1 or greater is 95 percent.
Daily flows:
Little Falls gage flow 2025-12-18: 911 MGD (1410 cfs)
Little Falls gage flow 2025-12-19: 1144 MGD (est., based on recently available real-time data) (1770 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2025-12-18: 1016 MGD (1572 cfs)
Point of Rocks flow 2025-12-19: 1163 MGD (est., based on recently available real-time data) (1800 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2025-12-18: 911 MGD (1410 cfs)
Note: Estimated flow below Great Falls intake is flow at Little Falls plus Little Falls water supply withdrawal.
Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2025-12-18):
Fairfax Water Corbalis withdrawal - Potomac: 91 MGD
WSSC Water Potomac withdrawal: 150 MGD
Washington Aqueduct withdrawal - Great Falls: 124 MGD
Washington Aqueduct withdrawal - Little Falls: 0 MGD
Loudoun Water withdrawal: 12 MGD
Loudoun Water Broad Run discharge: 12 MGD
Total Potomac withdrawal: 377 MGD
Total net Potomac withdrawal: 365 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1572 cfs
QPR, obs: 1572 cfs
QPR, WS: 0 cfs
Note to Loudoun Water: See NWS ensemble flow forecasts (HEFS, GEFS, NAEFS) for Point of Rocks flow for the next 7 days – https://www.weather.gov/erh/mmefs_marfc?id=PORM2&model=NAEFS. See US Army Corps of Engineers Potomac River Basin page for observed releases from Savage and Jennings Randolph reservoirs - https://water.usace.army.mil/office/nab/; See US Army Corps of Engineers North Branch Potomac River and Savage River page for scheduled releases - https://water.usace.army.mil/office/nab/releases/north-branch.
Note: Potomac River flow at Point of Rocks has dropped below the low-flow threshold of 2,000 cfs. When this occurs, per the Water Supply Coordination Agreement of 1982, CO-OP begins daily monitoring and reporting of Potomac flows and withdrawals on behalf of the CO-OP suppliers, Fairfax Water, Washington Aqueduct, and WSSC Water. Suppliers can review data at CO-OP's Data Portal at www.icprbcoop.org. Reports formatted in approved templates should be submitted by email to coop@icprb.org by 8:00 am for automated processing. Published monitoring reports are at http://icprbcoop.org/products/monitoring-reports.