Monitoring Reports

No appreciable rain fell in the basin over the past 24 hours. A trace amount, up to 0.1 inches, is expected over the next three days.

Daily flows:
Little Falls gage flow 2021-08-03: 1286 MGD (2390 cfs)
Little Falls gage flow 2021-08-04: 1195 MGD (est., based on recently available real time data) (2220 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2021-08-03: 904 MGD (1680 cfs)
Point of Rocks flow 2021-08-04: 893 MGD (est., based on recently available real time data) (1660 cfs)

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.

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.

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)

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.

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.

Though flow conditions are not yet of great concern, we intend to continue daily monitoring reports over the weekend, and would appreciate it if you can continue sending withdrawal and reservoir storage data.

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.

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.

Today, CO-OP is initiating daily drought monitoring because Potomac River flow at the US Geological Survey’s gage at Point of Rocks, Maryland, has fallen below CO-OP's daily monitoring trigger of 2000 cfs. According to National Weather Service's (NWS) quantitative precipitation forecasts, a little over a 1/10 of an inch of rain is expected in the basin over the next 3 days.

This concludes the 2020 Washington Metropolitan Area (WMA) drought exercise. A report describing exercise assumptions, activities, and tools will be prepared and made available on ICPRB's website in the coming weeks.

Thank you for your help in maintaining the reliability of the regional water supply system! Special thanks to WSSC Water staff for providing a tour of the Little Seneca Dam and to the Black Hill Regional Park for posting signs prior to the release.

We hope that the webinar on Forecast Informed Reservoir Operations by Hazen and Sawyer was informative.