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 (Saturday 2017-10-21)

No rain fell in the basin over the past 24 hours. Flow at Point of Rocks is currently at about 1900 cfs. The National Weather Service (NWS) 3-day forecast predicts accumulations of 0.01 to 0.10 inches in the western part of the Potomac basin. The NWS 5-day forecast predicts accumulations of up to 1.25 inches of rain in the Potomac basin.

Daily Flows:

Little Falls gage flow 2017-10-20: 1331 MGD (2060 cfs)

Little Falls gage flow 2017-10-21: 1280 MGD (est., based on recently available real time data) (1980 cfs)

Daily Potomac flow and demand update (Friday 2017-10-20)

Flow at Point of Rocks is currently at about 2000 cfs, CO-OP's trigger for daily drought monitoring. No rain fell in the basin over the past 24 hours, and no rain is expected over the next 72 hours, according to the Middle Atlantic River Forecast Center's quantitative precipitation forecasts. The National Weather Service (NWS) 5-day forecast predicts accumulations of up to 1.25 inches of rain in the Potomac basin.

Daily Flows:

Little Falls gage flow 2017-10-19: 1558 MGD (2410 cfs)

Daily Potomac flow and demand update (Friday 2017-10-13)

Point of Rocks flow is at 3110 cfs. Within the last 24 hours, the Potomac basin has received up to 0.1 inches of precipitation. The National Weather Service (NWS) 3-day forecast predicts accumulations of 0.25 inches of rain in the Potomac basin above Little Falls.

With rain continuing to fall across much of the basin, and Point of Rocks flow being above the low flow monitoring threshold of 2,000 cfs, daily monitoring will be discontinued until further notice. Thank you to all for your contribution to the monitoring efforts.

Daily Flows:

Daily Potomac flow and demand update (Thursday 2017-10-12)

The National Weather Service (NWS) 24 hour observed precipitation shows that there was 0.10 to 1.75 inches of rain in the Potomac basin above Little Falls. The NWS 3-day forecast predicts accumulations of 0.01 to 0.75 inches of rain over this same area. The US Geological Survey shows that Point of Rocks flow has remained above 2,000 cfs, our trigger for daily monitoring, since yesterday. The NWS Global Ensemble Forecast System simulations predict that flow at Point of Rocks will continue to rise above 2,000 cfs for the next couple of days.

Daily Potomac flow and demand update (Wednesday 2017-10-11)

The National Weather Service (NWS) 24 hour observed precipitation shows that there was 0.00 to 0.50 inches of rain in the Potomac basin above Little Falls. The NWS 3-day forecast predicts accumulations of 0.50 to 1.50 inches of rain over this same area. The US Geological Survey shows that Point of Rocks flow has been fluctuating around 2,000 cfs, our trigger for daily monitoring, since yesterday. The NWS Global Ensemble Forecast System simulations predict that flow at Point of Rocks will continue to rise above 2,000 cfs.

Daily Potomac flow and demand update (Tuesday 2017-10-10)

The National Weather Service (NWS) 24 hour observed precipitation shows that there was 0.00 to 1.50 inches of rain in the Potomac basin above Little Falls. The NWS 3-day forecast predicts accumulations of 0.25 to 1.25 inches of rain over this same area. The NWS Global Ensemble Forecast System simulations predict that flow at Point of Rocks will temporarily rise above 2,000 cfs, our trigger for daily drought monitoring, as earlier as sometime today.

Daily Flows:

Little Falls gage flow 2017-10-09: 1053 MGD (1630 cfs)

Daily Potomac flow and demand update (Monday 2017-10-09)

The National Weather Service (NWS) 24 hour observed precipitation shows that there was 0.25 to 1.75 inches of rain in the Potomac basin above Little Falls. The NWS 3-day forecast predicts accumulations of 0.40 to 1.75 inches of rain over this same area. The NWS Global Ensemble Forecast System simulations predict that flow at Point of Rocks will rise above 2,000 cfs, our trigger for daily drought monitoring, over the coming week.

Daily Flows:

Little Falls gage flow 2017-10-08: 860 MGD (1330 cfs)

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"# Net Potomac Withdrawals Actual and Forecast" "# FW_POT = Fairfax Water Corbalis Plant withdrawal from the Potomac, no Loudoun Water purchase water" "# WSSC_POT = Washington Subburban Sanitary Commission withdrawal from the Potomac" "# WA_GF = Washington Aqueduct withdrawal from Great Falls on the Potomac" "# WA_LF = Washington Aqueduct withdrawal from Little Falls on the Potomac" "# LW_POT = Loudoun Water Trap Rock Plant withdrawal from the Potomac" "# FW_OC = Occoquan off-Potomac withdrawal by Fairfax Water" "# WSSC_PA = Patuxent off-Potomac withdrawal by WSSC" "# LW_FW = Loudoun Water purchase water to add to Fairfax Water Potomac withdrawal" "# LW_BR = Loudoun Water Broad Run wastewater return flow" "# Total Annual Average Assumptions: FW = 138.82; WSSC = 158.43; WA = 120.72; LW = 23.86" "# Start Date = 2021-02-04" "# Stop Date = 2021-05-15" "# Time Zone = Eastern Standard Ttime (EST)" "# Units = million gallons per day (mgd)" DateTime,FW_POT,WSSC_POT,WA_GF,WA_LF,LW_POT,LW_FW,FW_OC,WSSC_PA,LW_BR 2021-02-03,73.36,95.49,107.17,0,5.97,12.42,69.41,72.85, 2021-02-04,77.64,98.36,101.29,0,6.56,12.42,70.21,72.78, 2021-02-05,69.42,93.04,95.63,0,5.32,12.42,70.21,72.58, 2021-02-06,74.14,92.97,100.46,0,4.89,13.07,70.19,72.39, 2021-02-07,74.58,92.93,107.67,0,6.04,13.07,70.36,72.21, 2021-02-08,70.39,92.53,111.21,0,5.08,13.07,71.55,72.36, 2021-02-09,67.96,103.65,113,0,5.28,13.07,70.07,64.68, 2021-02-10,78.45,92.59,105.71,0,4.98,13.07,69.53,62.36, 2021-02-11,64.26,92.05,101.38,0,4.48,13.07,71.27,65.24, 2021-02-12,64.53,92.29,97.29,0,4.86,13.07,70.5,60.63, 2021-02-13,64.91,93.55,101.79,0,5.11,13.07,70.39,68.2, 2021-02-14,74.4,93.3,104.13,0,5.14,13.07,71.55,64.23, 2021-02-15,65.04,93.21,100.96,0,5.07,13.07,71.92,62.93, 2021-02-16,82.84,91.08,112.83,0,4.78,13.07,71.57,71.88, 2021-02-17,49.97,91.45,107.29,0,4.84,13.07,70.21,71.84, 2021-02-18,55.38,91.54,62.47,0,5.61,13.07,70.75,66.39, 2021-02-19,59.16,92.32,103.49,0,5.33,13.07,64.61,57.61, 2021-02-20,57.43,92.57,101.64,0,4.35,13.07,68.35,65.64, 2021-02-21,69.89,101.42,109.73,0,5.88,13.07,69.99,70.53, 2021-02-22,63.37,96.59,125,0,12.42,8.19,70.21,64.89,6.78 2021-02-23,58.8,92.07,123.38,0,6.32,13.07,76.42,64.6, 2021-02-24,57.59,92.04,117.83,0,13.07,8.14,71.86,66.53,6.14 2021-02-25,57.34,91.43,132.67,0,4.81,13.07,71.99,63.88, 2021-02-26,57.72,92.12,126.92,0,4.25,13.07,72.3,63.79, 2021-02-27,54.28,91.5,119.88,0,4.19,13.07,72.8,66.57, 2021-02-28,52,90.98,107.92,0,6.87,13.07,72.09,63.37, 2021-03-01,61.96,130.56,116.38,0,6.62,13.07,72.24,18.4, 2021-03-02,61.98,154.71,110.92,0,7.05,13.07,71.55,0, 2021-03-03,79.93,159.92,120.71,0,6.94,13.07,72.15,0, 2021-03-04,80.18,157.2,107.52,0,6.79,13.07,72.2,0, 2021-03-05,81.26,140.33,104.12,0,6.02,13.07,72.15,15.6, 2021-03-06,85.04,93.54,100.1,0,6.25,13.07,72.13,64.15, 2021-03-07,94.21,99.37,105.87,0,7.66,13.07,66.16,58.79, 2021-03-08,82.36,94.17,109.08,0,7.56,13.07,75.44,58.88, 2021-03-09,89.09,94.08,109.41,0,7.7,13.07,72.07,63.49, 2021-03-10,87.66,93.94,109.64,0,7.57,13.07,71.98,57.06, 2021-03-11,88.77,93.9,109.48,0,7.55,13.07,71.98,57.48, 2021-03-12,85.83,94.02,105.06,0,6.39,13.07,71.6,63.66, 2021-03-13,86.66,93.6,100.09,0,6.33,13.07,71.52,64, 2021-03-14,55.19,91.94,113.29,0,7.48,13.07,72.27,60.22, 2021-03-15,82.59,91.98,62,0,7.2,13.07,71.73,60.21, 2021-03-16,83.52,92.76,108.9,0,6.61,13.07,72.43,57.95, 2021-03-17,78.64,92.19,106.7,0,6.41,13.07,71.1,55.17, 2021-03-18,81.08,93.29,105.52,0,6.38,13.07,69.21,50.21, 2021-03-19,79.77,92.72,102.76,0,5.65,13.07,71.38,47.65, 2021-03-20,82,93.47,98.47,0,5.85,13.07,73.42,52.84, 2021-03-21,86.27,93.51,105.06,0,7.37,13.07,73.42,60.66, 2021-03-22,79.57,91.41,108.39,0,6.46,13.07,73.81,64.95, 2021-03-23,80.52,92.56,106.82,0,6.71,13.07,73.81,58.74, 2021-03-24,59.99,91.79,115.29,0,6.84,13.07,72.41,50.96, 2021-03-25,57.58,91.53,114.08,0,7.05,13.07,71.91,51.75, 2021-03-26,56.7,91.2,110.96,0,7.3,11.04,71.99,59.1, 2021-03-27,57.72,91.62,111.54,0,7.61,11.04,72.15,58.95, 2021-03-28,54.43,91.77,121.08,0,8.97,11.04,72.2,59.02, 2021-03-29,52.8,92.74,121.42,0,8.14,11.04,72.15,58.71, 2021-03-30,50.85,92.13,117.38,0,8.03,11.04,72.13,58.97, 2021-03-31,57.27,92.46,112,0,11.21,11.04,66.16,52.91, 2021-04-01,52.62,93.51,114.96,0,11.25,11.04,75.44,47.34, 2021-04-02,55.56,92.75,115.17,0,10.63,11.04,72.07,48.25, 2021-04-03,50.66,93.45,105.63,0,10.96,11.04,71.98,57.41, 2021-04-04,56.82,93.33,112.04,0,12.55,11.04,71.98,56.57, 2021-04-05,65.36,90.39,118.71,0,12.53,11.04,71.6,58.92, 2021-04-06,71.1,90.35,106.57,0,12.8,11.04,71.52,62.24, 2021-04-07,72.19,90.22,116.42,0,11.72,11.04,71.55,61.3, 2021-04-08,70.93,89.71,121.67,0,7.77,14.82,71.73,63.49, 2021-04-09,58.63,89.64,127.04,0,6.39,14.82,72.43,56.54, 2021-04-10,52.38,89.4,109.96,0,6.75,14.82,71.1,54.48, 2021-04-11,62.34,103.35,122.43,0,8.36,14.82,69.21,55.63, 2021-04-12,69.89,101.35,109.28,0,7.41,14.82,71.38,54.09, 2021-04-13,70.13,87.63,109.83,0,7.85,14.82,73.42,55.71, 2021-04-14,97,98.57,120.92,0,7.91,14.82,69.67,62.14, 2021-04-15,74.87,91.59,114.46,0,7.92,14.82,73.81,52.16, 2021-04-16,96.42,91.66,108.29,0,7.18,14.82,73.04,58.74, 2021-04-17,75.41,100.08,113.79,0,7.3,14.82,71.82,58.88, 2021-04-18,71.23,95.97,109.46,0,8.82,14.82,75.72,59.1, 2021-04-19,77.56,101.96,125.46,0,8.85,14.82,77.54,52.59, 2021-04-20,72.51,102.15,124.21,0,8.94,14.82,76.79,47.14, 2021-04-21,67.22,99.6,119.5,0,11.04,14.65,74.84,56.21,6.83 2021-04-22,72.71,88.24,125.88,0,8.44,14.82,71.92,66.73, 2021-04-23,69.49,97.33,117.29,0,6.85,14.82,71.69,63.08, 2021-04-24,72.44,92.57,120.67,0,7.6,14.82,74.22,63.47, 2021-04-25,64.07,92.11,96.5,0,9.28,14.82,75.71,61.88, 2021-04-26,71.11,92.52,118.17,0,9.35,14.82,73.99,62.44, 2021-04-27,79.34,98.53,126.25,0,9.7,14.82,72.39,68.52, 2021-04-28,86.6,98.83,127.42,0,9.52,14.82,74.79,68.81, 2021-04-29,80.64,103.15,136,0,9.44,14.82,80.95,66.09, 2021-04-30,74.02,95.83,144.88,0,15.26,11.52,73.76,62.66, 2021-05-01,78.9,90.97,117.63,0,14.82,10.16,74.16,62.57,6.3 2021-05-02,83.9,106.14,121,0,16.21,11.52,74.18,62.36, 2021-05-03,82.24,99.12,125.29,0,15.68,11.52,74.04,56.17, 2021-05-04,72.01,103.78,128.04,0,16.07,11.52,73.42,54.64, 2021-05-05,73.65,98.23,126.63,0,15.22,11.52,74.38,54.08, 2021-05-06,71.24,91.46,92.75,0,15.46,11.52,72.29,57.96, 2021-05-07,76.42,97.65,124.42,0,14.64,11.52,70.87,61.82, 2021-05-08,56.58,96.64,123,0,15.21,11.52,69.67,55.89, 2021-05-09,63.09,90.65,109.33,0,16.85,11.52,69.96,51.45, 2021-05-10,84.6,101.07,123.92,0,16.59,11.52,73.04,51.26, 2021-05-11,69.56,103.42,125.88,0,17.18,11.52,75.42,51.22, 2021-05-12,85.14,105.09,139.96,0,17.21,11.52,73.72,50.84, 2021-05-13,74.5,105.1,137.46,0,17.2,11.52,77.07,55.11, 2021-05-14,89.85,102.18,136.33,0,16.36,11.52,75.98,55.63,