Monitoring Reports

During periods of drought, the Cooperative Water Supply Operations on the Potomac (CO-OP) helps manage the Washington metropolitan area water supply system by coordinating withdrawals from the Potomac River and off-river reservoirs and recommending releases from upstream reservoirs when forecasted flow in the river is not sufficient to meet expected needs. These needs include water demands and an environmental flow-by of 100 million gallons per day (MGD) on the Potomac River at Little Falls dam near Washington, D.C.

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Daily Potomac flow and demand update (Tuesday 2021-08-03)

According to MARFC, no precipitation fell in the basin over the last 24 hours. A trace amount, up to 0.1 inches, is expected over the next three days.

Note a correction to Washington Aqueduct's reported 7/31 withdrawal. The reported number was 121 MGD while the correct number was 132 MGD.

Daily Potomac flow and demand update (Monday 2021-08-02)

About 0.1 inches of rain fell in the basin over the past 24 hours; a trace to 0.25 inches is expected over the next three days.

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: 0.08 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.16 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.52 (inches)

Daily Potomac flow and demand update (Sunday 2021-08-01)

No appreciable rain fell in the basin over the past 24 hours; a trace to 0.25 inches is expected over the next three days.

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 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.31 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.45 (inches)

Daily Potomac flow and demand update (Saturday 2021-07-31)

Flow in the river has held fairly steady over the past several days, at around 1800 cfs at Point of Rocks, and according to National Weather Service forecasts this will continue to be the case for the upcoming week. No appreciable precipitation fell over the basin during the past 24 hours. The Washington metropolitan area may receive up to an inch of rain over the next 3 days, but much less rain is expected west of the metro area.

Daily Potomac flow and demand update (Friday 2021-07-30)

Daily Potomac flow and demand update (Friday 2021-07-30)
The basin received almost a ¼ inch of rain over the last 24 hours. Little rain is expected in the portion of the watershed above Little Falls over the next three days. According to Middle Atlantic River Forecast Center ensemble flow forecasts, flow at Point of Rocks is expected to remain above 1800 cfs over the weekend.

Daily Potomac flow and demand update (Thursday 2021-07-29)

The 3-day forecast (MARFC) estimates 0.01 to 0.1 inches of rainfall in most of the Potomac Basin. There is a chance that the North Branch may receive up to 0.5 an inch of rainfall. According to our recent basin-wide average precipitation, the basin received 0.03 inches of rain in the past 24 hours. The Little Falls gage is now reporting. The gage antenna had been blocked by a broken-down crane.

Second day of CO-OP daily drought monitoring - Daily Potomac flow and demand update (Wednesday 07/28/2021)

Daily Potomac flow and demand update (Wednesday 2021-07-28)
Potomac basin flows continue to slowly decline. The Middle Atlantic River Forecast Center predicts that from 0.10 to 0.75 inches of rain will fall over the basin over the next three days. The Potomac River gage at Little Falls is currently not reporting real-time flows and CO-OP is notifying USGS that this gage is down.

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