Situational Awareness (Monday, 2023-11-20)
According to the Middle Atlantic River Forecast Center, the basin will be dry on Monday and then receive rain on Tuesday. The following 3-day basin average precipitation total is 1.6 inches, with possible precipitation in the 1 to 2 inches range. This precipitation forecast may produce river and creek rises in streamflow on Tuesday and Wednesday. Currently, Shepherdstown and Point of Rocks USGS gage flows remain steady.
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 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.14 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.14 (inches)
Daily flows:
Little Falls gage flow 2023-11-19: 704 MGD (1090 cfs)
Little Falls gage flow 2023-11-20: 692 MGD (est., based on recently available real-time data) (1070 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-11-19: 905 MGD (1400 cfs)
Point of Rocks flow 2023-11-20: 892 MGD (est., based on recently available real-time data) (1380 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2023-11-19: 704 MGD (1089 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 (2023-11-19):
Fairfax Water Corbalis withdrawal - Potomac: 79 MGD
WSSC Water Potomac withdrawal: 139 MGD
Washington Aqueduct withdrawal - Great Falls: 119 MGD
Washington Aqueduct withdrawal - Little Falls: 0 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 342 MGD
Total net Potomac withdrawal: 335 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1400 cfs
QPR, obs: 1400 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.