Monitoring Reports

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.

This is the third and last day of our 2020 Washington metropolitan area (WMA) annual drought exercise. Reported below are actual recent conditions and simulated drought operations.

Today we requested a simulated Little Seneca release of 22 MGD. This was based on the drought scenario and not yesterday’s actual release. We will provide analysis on the travel time of this test release in our report. You can follow the release at the USGS gage 01645000 SENECA CREEK AT DAWSONVILLE, MD here.

**************************

RECENT CONDITIONS – ACTUAL

An actual Little Seneca test release was initiated this morning at 10:00 AM. The planned release rate was 400 MGD, but during ramping up the release, it was found that the maximum possible rate is 275 MGD. You can follow the release at the USGS 01645000 SENECA CREEK AT DAWSONVILLE, MD here: https://waterdata.usgs.gov/usa/nwis/uv?01645000.

Our afternoon report appears below. Note that an ACTUAL test release from Little Seneca Reservoir has been approved by the CO-OP General Managers and is planned to be initiated tomorrow morning at 10 AM at a rate of 400 million gallons per day (MGD) and continued for 12 hours. Due to this release, flow in Seneca Creek will be elevated between approximately 10 AM on November 17 and 6 AM on November 18.

**************************
RECENT CONDITIONS – ACTUAL