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 (Friday 2019-09-27)

According to Middle Atlantic River Forecast Center estimates, little or no rain fell in the Potomac basin over the past 72 hours. According to forecasts, no significant rain is expected for the next 7 days.

Daily Potomac flow and demand update (Thursday 2019-09-26)

Yesterday brought no relief from the dry conditions in the Potomac basin. The National Weather Service forecasts negligible accumulations of precipitation over the next 7 days.

Daily Flows:

Little Falls gage flow 2019-09-25: 1060 MGD (1640 cfs)

Little Falls gage flow 2019-09-26: 1034 MGD (est., based on recently available real time data) (1600 cfs)

Note: Gage flow at Little Falls is measured after water supply withdrawals.

Point of Rocks flow 2019-09-25: 1170 MGD (1810 cfs)

Daily Potomac flow and demand update (Wednesday 2019-09-25)

Dry conditions persist, with negligible precipitation in the Potomac basin over the past several days. The National Weather Service's forecast calls for little rain over the next 7 days.

Daily Flows:

Little Falls gage flow 2019-09-24: 1053 MGD (1630 cfs)

Little Falls gage flow 2019-09-25: 1034 MGD (est., based on recently available real time data) (1600 cfs)

Note: Gage flow at Little Falls is measured after water supply withdrawals.

Point of Rocks flow 2019-09-24: 1144 MGD (1770 cfs)

Daily Potomac flow and demand update (Tuesday 2019-09-24)

The Potomac remains dry with 2.8 inches below normal basin average precipitation over the past 30 days. The Middle Atlantic River Forecast Center's 24 and 72 hour precipitation forecast shows 0 to 0.1 inch of precipitation over isolated parts of the basin. The 7-day total precipitation forecast shows 0 to 0.1 inch of precipitation over most of the basin.

Daily Flows:

Little Falls gage flow 2019-09-23: 1034 MGD (1600 cfs)

Little Falls gage flow 2019-09-24: 1034 MGD (est., based on recently available real time data) (1600 cfs)

Initiated Monitoring - Daily Potomac flow and demand update (Monday 2019-09-23)

Potomac River flow at Point of Rocks has dropped below the low-flow threshold of 2,000 cfs. Today CO-OP is initiating daily monitoring and reporting of Potomac flows and withdrawals. Today's report appears below.

Conditions have been dry throughout the basin over the past couple of months. National Weather Service precipitation estimates indicate that the basin received no appreciable rain over the past 7 days, and forecasts call for little rain over the next seven days.

Daily Flows:

Little Falls gage flow 2019-09-22: 1125 MGD (1740 cfs)

​​Discontinue Monitoring - Daily Potomac flow and demand update (Monday 2017-10-30)

The National Weather Service (NWS) 24 hour observed precipitation shows that there was between 0.10 and 3.00 inches of precipitation in the Potomac basin above Little Falls. The NWS 3-day and 5-day forecasts both predict 0.00 to 0.25 inches of rain in this same area.

Daily Potomac flow and demand update (Sunday 2017-10-29)

According to the Middle Atlantic River Forecast Center (MARFC), portions of the basin received no rain or trace amounts over the last 24 hours, and the northwestern edge of the basin received up to 2 inches. Over the next day, MARFC predicts 1 to 1 3/4 inches in the drainage area above Little Falls dam. Although flow at the US Geological Survey gage at Point of Rocks is currently above 2,000 cfs, our trigger for daily monitoring, we will continue daily monitoring efforts until we see that flows have significantly improved for several days.

Daily Flows:

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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,