Situational Awareness (Saturday, 2024-07-20)
No appreciable rainfall has fallen in the basin over the past 24 hours. According to the Middle Atlantic River Forecast Center predictions, the next 24 hours may see 0.1 inches of rain and the next three days may see about 0.2 inches of rain. The week-long outlook expects a total of approximately 1 inch of rain in the basin.
Special Conditions
The inspection work, contracted by the National Park Service, performed on July 16th and 17th at Dams 4 and 5 is continuing to impact downstream flows and cause intra-daily fluctuations, although the amplitude of the fluctuations is decreasing.
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: 0.25 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.44 (inches)
Daily flows:
Little Falls gage flow 2024-07-19: 763 MGD (1180 cfs)
Little Falls gage flow 2024-07-20: 711 MGD (est., based on recently available real-time data) (1100 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2024-07-19: 879 MGD (1360 cfs)
Point of Rocks flow 2024-07-20: 879 MGD (est., based on recently available real-time data) (1360 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2024-07-19: 785 MGD (1215 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 (2024-07-19):
Fairfax Water Corbalis withdrawal - Potomac: 124 MGD
WSSC Water Potomac withdrawal: 142 MGD
Washington Aqueduct withdrawal - Great Falls: 137 MGD
Washington Aqueduct withdrawal - Little Falls: 22 MGD
Loudoun Water withdrawal: 13 MGD
Loudoun Water Broad Run discharge: 6 MGD
Total Potomac withdrawal: 438 MGD
Total net Potomac withdrawal: 432 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1360 cfs
QPR, obs: 1360 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.