Situational Awareness (Thursday, 2024-07-18)
According to the Middle Atlantic River Forecast Center predictions, the next three days may see 0.1 inches of rain. The week-long outlook expects a total of approximately 0.9 inches of rain in the basin.
Special Conditions
Intra-daily flow fluctuations have been observed at Point of Rocks, with flows temporarily increasing and then falling to a new low before leveling out, and at Little Falls, with flows currently rising, due to the diving inspections performed on the upstream side of Dam No. 4 on July 16th and Dam No. 5 on July 17th by a National Parks Service contractor.
The provisional status associated with the WSSC Potomac withdrawals and total net Potomac withdrawals for July 16th are due to a power outage that WSSC Water experienced between the afternoon of July 15th and the morning of July 16th.
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: 0.18 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.29 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.47 (inches)
Daily flows:
Little Falls gage flow 2024-07-17: 795 MGD (1230 cfs)
Little Falls gage flow 2024-07-18: 1015 MGD (est., based on recently available real-time data) (1570 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2024-07-17: 950 MGD (1470 cfs)
Point of Rocks flow 2024-07-18: 847 MGD (est., based on recently available real-time data) (1310 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2024-07-17: 964 MGD (1492 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 (2024-07-17):
Fairfax Water Corbalis withdrawal - Potomac: 130 MGD
WSSC Water Potomac withdrawal: 158 MGD
Washington Aqueduct withdrawal - Great Falls: 0 MGD
Washington Aqueduct withdrawal - Little Falls: 169 MGD
Loudoun Water withdrawal: 13 MGD
Loudoun Water Broad Run discharge: 5 MGD
Total Potomac withdrawal: 470 MGD
Total net Potomac withdrawal: 466 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1470 cfs
QPR, obs: 1470 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.