Situational Awareness (Monday, 2026-09-21)
0.1 to 0.5 inches of rain fell in the basin over the past 24 hours, primarily in the western portion of the basin. According to the Middle Atlantic River Forecast Center, chances for rain will persist throughout the week, with widespread showers expected Tuesday. Forecast rainfall through Wednesday morning ranges from 0.5 to 2.5 inches, with amounts exceeding 1 inch expected across western and southern Pennsylvania, Maryland, and Virginia.
Special Conditions
The U.S. Army Corps of Engineers, Baltimore District, reports that the final scheduled whitewater release from Savage River Dam for 2026 will occur on Saturday, September 26. The 2026 water-quality release schedule for Jennings Randolph and Savage reservoirs is available here: https://water.usace.army.mil/office/nab/releases/north-branch .
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 2026-09-20: 892 MGD (1380 cfs)
Little Falls gage flow 2026-09-21: 885 MGD (est., based on recently available real-time data) (1370 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2026-09-20: 995 MGD (1540 cfs)
Point of Rocks flow 2026-09-21: 995 MGD (est., based on recently available real-time data) (1540 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2026-09-20: 892 MGD (1380 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 (2026-09-20):
Fairfax Water Corbalis withdrawal - Potomac: 96 MGD
WSSC Water Potomac withdrawal: 129 MGD
Washington Aqueduct withdrawal - Great Falls: 128 MGD
Washington Aqueduct withdrawal - Little Falls: 0 MGD
Loudoun Water withdrawal: 12 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 364 MGD
Total net Potomac withdrawal: 357 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1540 cfs
QPR, obs: 1540 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.