Situational Awareness (Tuesday, 2024-09-17)
The forecast from several days ago of significant rainfall never materialized. A small amount of rain is expected in the Potomac basin over the coming days. According to Middle Atlantic River Forecast Center predictions, average basin rainfall will be around 0.5 inches over the next three days and 0.6 inches over the next 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 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0 (inches)
Daily flows:
Little Falls gage flow 2024-09-16: 873 MGD (1350 cfs)
Little Falls gage flow 2024-09-17: 937 MGD (est., based on recently available real-time data) (1450 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2024-09-16: 969 MGD (1500 cfs)
Point of Rocks flow 2024-09-17: 1073 MGD (est., based on recently available real-time data) (1660 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2024-09-16: 921 MGD (1425 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 (2024-09-16):
Fairfax Water Corbalis withdrawal - Potomac: 124 MGD
WSSC Water Potomac withdrawal: 126 MGD
Washington Aqueduct withdrawal - Great Falls: 92 MGD
Washington Aqueduct withdrawal - Little Falls: 48 MGD
Loudoun Water withdrawal: 13 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 403 MGD
Total net Potomac withdrawal: 397 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1500 cfs
QPR, obs: 1500 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.