Situational Awareness (Friday, 2023-11-10):
Yesterday, the Potomac received 0.1 inches of basin average precipitation. Over the next three days, the NWS Middle Atlantic River Forecast Center anticipates approximately 0.1 inches of light basin average precipitation, with varying amounts reaching different parts of the basin. NWS maps suggest that the North and South Forks of Shenandoah, currently experiencing "extreme drought" conditions according to the U.S. Drought Monitor's D3 classification, may receive up to 0.25 inches of this rain. It's important to note that river levels remain significantly below their normal levels across the region. You can view the U.S. Geological Survey data in the MARFC graphic here: https://www.weather.gov/images/marfc/graphicalHMD/graphicalHMD.png.
The large fluctuation in river flows associated with the bathymetric survey conducted at Potomac Dam No. 5 appears to have steadied at Point of Rocks.
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: 0.1 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.1 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.1 (inches)
Daily flows:
Little Falls gage flow 2023-11-09: 672 MGD (1040 cfs)
Little Falls gage flow 2023-11-10: 717 MGD (est., based on recently available real-time data) (1110 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-11-09: 743 MGD (1150 cfs)
Point of Rocks flow 2023-11-10: 860 MGD (est., based on recently available real-time data) (1330 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2023-11-09: 672 MGD (1040 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 (2023-11-09):
Fairfax Water Corbalis withdrawal - Potomac: 74 MGD
WSSC Water Potomac withdrawal: 134 MGD
Washington Aqueduct withdrawal - Great Falls: 137 MGD
Washington Aqueduct withdrawal - Little Falls: 0 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 350 MGD
Total net Potomac withdrawal: 344 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1150 cfs
QPR, obs: 1150 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.