Situational Awareness (Wednesday, 2024-07-10)
The Middle Atlantic River Forecast Center expects some rain with localized thunderstorms starting today. According to their predictions, the next 24 hours may see 0.1 inches of rain. Over the next 3 days, the average basin rainfall may be around 0.4 inches. The week-long outlook expects a total of approximately 0.6 inches of rain in the basin. Any rainfall will be combating the impacts of evaporation and the increased demand from outdoor watering due to the excessive heat currently affecting the Potomac Basin.
Special Conditions
The whitewater release from Savage Reservoir last Sunday (2024-07-07) is currently flowing past the USGS streamflow gages on the Potomac River at Hancock. The impact on flow is brief, less than a day.
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: 0.04 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.05 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.31 (inches)
Daily flows:
Little Falls gage flow 2024-07-09: 937 MGD (1450 cfs)
Little Falls gage flow 2024-07-10: 847 MGD (est., based on recently available real-time data) (1310 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2024-07-09: 1150 MGD (1780 cfs)
Point of Rocks flow 2024-07-10: 1163 MGD (est., based on recently available real-time data) (1800 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2024-07-09: 1093 MGD (1692 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 (2024-07-09):
Fairfax Water Corbalis withdrawal - Potomac: 143 MGD
WSSC Water Potomac withdrawal: 162 MGD
Washington Aqueduct withdrawal - Great Falls: 0 MGD
Washington Aqueduct withdrawal - Little Falls: 156 MGD
Loudoun Water withdrawal: 14 MGD
Loudoun Water Broad Run discharge: 5 MGD
Total Potomac withdrawal: 475 MGD
Total net Potomac withdrawal: 470 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1780 cfs
QPR, obs: 1780 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.