A little under a half inch of rain fell yesterday in Potomac watershed above Little Falls and up to ¼ inch is forecast over the next three days. Average river flow yesterday at Point of Rocks was just 2000 cfs, CO-OP’s threshold for daily monitoring. It’s likely that flows will rise slightly above this level over the next week due to the recent and forecasted rainfall. However, flows are low for this time of year, so CO-OP will continue daily drought monitoring until a significant increase occurs.
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 multi-sensor precipitation estimates)
Yesterday's area-weighted average basin precipitation: 0.45 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.45 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.49 (inches)
Daily flows:
Little Falls gage flow 2023-06-12: 1150 MGD (1780 cfs)
Little Falls gage flow 2023-06-13: 1234 MGD (est., based on recently available real-time data) (1910 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-06-12: 1293 MGD (2000 cfs)
Point of Rocks flow 2023-06-13: 1306 MGD (est., based on recently available real-time data) (2020 cfs)
Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-06-12):
Fairfax Water Corbalis withdrawal (Potomac): 118 MGD
WSSC Water Potomac withdrawal: 145 MGD
Washington Aqueduct withdrawal: 148 MGD
Loudoun Water withdrawal: 14 MGD
Loudoun Water Broad Run discharge: 6 MGD
Total Potomac withdrawal: 425 MGD
Total net Potomac withdrawal: 419 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 2000 cfs
QPR, obs: 2000 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 – see https://www.weather.gov/erh/mmefs_marfc?id=PORM2&model=NAEFS.
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.