Situational Awareness (Thursday, 2024-09-12)
According to the Middle Atlantic River Forecast Center predictions, the next 24 hours may see 0 inches of rain. Over the next 3 days, the average basin rainfall may be around 0 inches. The week-long outlook expects a total of approximately 0.2 to 0.7 inches of rain in the basin.
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: 0.06 (inches)
Special Conditions:
NPS has a contractor that will be performing bathymetric surveys at Potomac Dam No. 4 in Washington County, MD on Thursday, September 12, 2024. During this time, the hydroelectric operator – Eagle Creek will be diverting water off of the run-of-river dam crest through the turbines. This should be the last day that NPS will be diverting water off of the dam this year, since the time of year restriction for the eels begins September 15.
Daily flows:
Little Falls gage flow 2024-09-11: 1150 MGD (1780 cfs)
Little Falls gage flow 2024-09-12: 1034 MGD (est., based on recently available real-time data) (1600 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2024-09-11: 1202 MGD (1860 cfs)
Point of Rocks flow 2024-09-12: 1202 MGD (est., based on recently available real-time data) (1860 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2024-09-11: 1217 MGD (1883 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 (2024-09-11):
Fairfax Water Corbalis withdrawal - Potomac: 124 MGD
WSSC Water Potomac withdrawal: 130 MGD
Washington Aqueduct withdrawal - Great Falls: 89 MGD
Washington Aqueduct withdrawal - Little Falls: 67 MGD
Loudoun Water withdrawal: 13 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 423 MGD
Total net Potomac withdrawal: 416 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1860 cfs
QPR, obs: 1860 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.