Situational Awareness (Tuesday, 2023-11-21)
Dry conditions have continued, though Potomac River flows have been holding relatively steady in recent weeks. Forecasts call for a substantial amount of rain in the Potomac basin over the coming days: approximately 1.3 inches over the next 24 hours and 2 inches over the next 3 days. We hope this doesn’t cause too much of a problem for your family’s Thanksgiving travel plans, but we are grateful for getting some relief from this drought!
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: 0.1 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.14 (inches)
Daily flows:
Little Falls gage flow 2023-11-20: 698 MGD (1080 cfs)
Little Falls gage flow 2023-11-21: 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 2023-11-20: 892 MGD (1380 cfs)
Point of Rocks flow 2023-11-21: 879 MGD (est., based on recently available real-time data) (1360 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2023-11-20: 698 MGD (1080 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 (2023-11-20):
Fairfax Water Corbalis withdrawal - Potomac: 76 MGD
WSSC Water Potomac withdrawal: 139 MGD
Washington Aqueduct withdrawal - Great Falls: 125 MGD
Washington Aqueduct withdrawal - Little Falls: 0 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 345 MGD
Total net Potomac withdrawal: 338 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1380 cfs
QPR, obs: 1380 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.