Situational Awareness (Sunday, 2026-01-11):
According to the Middle Atlantic River Forecast Center (MARFC), 0.25 to 1.25 inches of precipitation fell across much of the Potomac watershed yesterday, consistent with the rainfall discussed in yesterday’s discussion. Runoff from this event is beginning to register at upstream gages, but a corresponding response has not yet been observed at Point of Rocks. Over the next three days, average basin precipitation is only expected to range from 0.01 to 0.25 inches in the upper portions of the basin, with a possibility of totals reaching up to 0.75 inches over the next seven days. MARFC forecasts suggest any increases in river flows are expected to be temporary, with limited sustained relief from low-flow conditions.
Special Conditions:
None
Daily flows:
Little Falls gage flow 2026-01-10: 1370 MGD (2120 cfs)
Little Falls gage flow 2026-01-11: 1978 MGD (est., based on recently available real-time data) (3060 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2026-01-10: 1105 MGD (1710 cfs)
Point of Rocks flow 2026-01-11: 1099 MGD (est., based on recently available real-time data) (1700 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2026-01-10: 1370 MGD (2120 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 (2026-01-10):
Fairfax Water Corbalis withdrawal - Potomac: 88 MGD
WSSC Water Potomac withdrawal: 135 MGD
Washington Aqueduct withdrawal - Great Falls: 118 MGD
Washington Aqueduct withdrawal - Little Falls: 0 MGD
Loudoun Water withdrawal: 9 MGD
Loudoun Water Broad Run discharge: 8 MGD
Total Potomac withdrawal: 349 MGD
Total net Potomac withdrawal: 341 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1710 cfs
QPR, obs: 1710 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.