Situational Awareness (Wednesday, 2024-09-18)
The remnants of Potential Tropical Cyclone Eight is bringing rainfall to Maryland, Virginia, and West Virginia. According to the Middle Atlantic River Forecast Center, the next 24 hours could see 0.7 inches of basin average rain. Over the next 3 days, average basin rainfall is predicted to be around 0.8 inches, with a total of approximately 0.9 inches expected over the week.
Special Conditions
None
Recent basin-wide average precipitation (above Little Falls):
(based on CO-OP's Low Flow Forecast System analysis of Middle Atlantic River Forecast Center (MARFC) gridded multisensor precipitation estimates)
Yesterday's area-weighted average basin precipitation: 0.08 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.08 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.08 (inches)
Daily flows:
Little Falls gage flow 2024-09-17: 866 MGD (1340 cfs)
Little Falls gage flow 2024-09-18: 982 MGD (est., based on recently available real-time data) (1520 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2024-09-17: 1008 MGD (1560 cfs)
Point of Rocks flow 2024-09-18: 1047 MGD (est., based on recently available real-time data) (1620 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2024-09-17: 904 MGD (1398 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 (2024-09-17):
Fairfax Water Corbalis withdrawal - Potomac: 100 MGD
WSSC Water Potomac withdrawal: 116 MGD
Washington Aqueduct withdrawal - Great Falls: 89 MGD
Washington Aqueduct withdrawal - Little Falls: 38 MGD
Loudoun Water withdrawal: 13 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 356 MGD
Total net Potomac withdrawal: 348 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1560 cfs
QPR, obs: 1560 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://www.nab-wc.usace.army.mil/nab/poto.html; See US Army Corps of Engineers North Branch Potomac River and Savage River page for scheduled releases - https://www.nab-wc.usace.army.mil/nab/northBranch.html.
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.