Daily Potomac flow and demand update (Friday 2021-08-13)

Zero precipitation occurred in the basin over the past 24 hours. The Potomac basin has been experiencing a heat advisory that is expected to continue into today.

The NWS-Mid-Atlantic River Forecast Center (NWS-MARFC) has issued a Hazardous Weather Outlook for the Maryland portion of the Chesapeake Bay, Tidal Potomac River, and I-95 corridor through central Maryland, northern Virginia, and District of Columbia. In the next 2 to 7 days, isolated severe storms to heavy rains are possible due to Tropical Depression Fred. There is still a great deal of uncertainty regarding the storm track and any rainfall amounts in this region. The 5 and 7-day precipitation forecasts suggest we may see 0.75 to around 2 inches of rain. At this point, it is too early to discuss specific rivers that may be impacted by flooding. The NWS-MARFC expects to have a better idea of specific Mid-Atlantic impacts this Saturday or Sunday.

Daily flows:
Little Falls gage flow 2021-08-12: 1196 MGD (1850 cfs)
Little Falls gage flow 2021-08-13: 1125 MGD (est., based on recently available real time data) (1740 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2021-08-12: 1131 MGD (1750 cfs)
Point of Rocks flow 2021-08-13:1202 MGD (est., based on recently available real time data) (1860 cfs)

Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2021-08-12):
Fairfax Water Corbalis withdrawal (Potomac): 104 MGD
WSSC Water Potomac withdrawal: 119 MGD
Washington Aqueduct withdrawal: 147 MGD
Loudoun Water withdrawal: 12 MGD
Loudoun Water Broad Run discharge: 4 MGD
Total Potomac withdrawal: 383 MGD
Total net Potomac withdrawal: 379 MGD

Loudoun Water drought operations protocol river flow values (based on yesterday's flows):
QPR: 1750 cfs
QPR, obs: 1750 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 conducting daily monitoring and reporting of Potomac flows and withdrawals on behalf of the CO-OP suppliers, Fairfax Water, Washington Aqueduct, and WSSC Water. Reports formatted in approved templates should be submitted by email to coop@icprb.org by 8:00 am, for automated processing. Data can be reviewed by suppliers at CO-OP's Data Portal at www.icprbcoop.org. Monitoring emails can be viewed at https://icprbcoop.org/drupal4/data-products/monitoring-reports.