Situational Awareness (Thursday, 2026-09-17)
No appreciable rain has fallen in the basin over the past 24 hours. According to the Middle Atlantic River Forecast Center predictions, the next 24 hours may see between 0.1 to 0.5 inches of rain. The week-long outlook expects a total of approximately 1 to 2 inches of rain in the basin.
Special Conditions
Intra-daily flow fluctuations at Potomac River gages, including Point of Rocks, are occurring due to upstream dam operations associated with eel passage.
Daily flows:
Little Falls gage flow 2026-09-16: 931 MGD (1440 cfs)
Little Falls gage flow 2026-09-17: 840 MGD (est., based on recently available real-time data) (1300 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2026-09-16: 1041 MGD (1610 cfs)
Point of Rocks flow 2026-09-17: 1125 MGD (est., based on recently available real-time data) (1740 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2026-09-16: 931 MGD (1440 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 (2026-09-16):
Fairfax Water Corbalis withdrawal - Potomac: 117 MGD
WSSC Water Potomac withdrawal: 159 MGD
Washington Aqueduct withdrawal - Great Falls: 148 MGD
Washington Aqueduct withdrawal - Little Falls: 0 MGD
Loudoun Water withdrawal: 12 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 436 MGD
Total net Potomac withdrawal: 429 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1610 cfs
QPR, obs: 1610 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.