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 2017-10-28)

The National Weather Service (NWS) reports that there was no precipitation in the Potomac basin over the last 24 hours. The NWS 3-day forecast predicts 1.25 to 2.0 inches of rain in the portion of the basin above Little Falls dam. Although flows 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:

Little Falls gage flow 2017-10-27: 1545 MGD (2390 cfs)

Daily Potomac flow and demand update (Friday 2017-10-27)

The National Weather Service (NWS) 24 hour observed precipitation shows that there were scattered, trace amounts of rain in the Potomac basin above Little Falls. The NWS 3-day forecast predicts 0.75 to 1.5 inches of rain in this same area. The National Weather Service (NWS) 5-day forecast predicts accumulations of up to 2.5 inches of rain in the Potomac basin.

Daily Potomac flow and demand update (Thursday 2017-10-26)

The National Weather Service (NWS) 24 hour observed precipitation shows that there were scattered, trace amounts of rain in the Potomac basin above Little Falls. The NWS 3-day forecast predicts 0 to 0.5 inches of rain in this same area with the largest amounts expected in the western portions of the basin. The National Weather Service (NWS) 5-day forecast predicts accumulations of up to 1.75 inches of rain in the Potomac basin.

Daily Potomac flow and demand update (Wednesday 2017-10-25)

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 no rain over the majority of this same area. The US Geological Survey shows that Point of Rocks flow fell below and then rose 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:

Little Falls gage flow 2017-10-24: 1247 MGD (1930 cfs)

Daily Potomac flow and demand update (Tuesday 2017-10-24)

The National Weather Service (NWS) 24 hour observed precipitation shows that there was 0.01 to 1.25 inches of rain in the Potomac basin above Little Falls. The NWS 3-day forecast predicts accumulations of 0.25 to 1.50 inches of rain over this same area. The US Geological Survey shows that Point of Rocks flow rose 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:

Little Falls gage flow 2017-10-23: 1099 MGD (1700 cfs)

Daily Potomac flow and demand update (Monday 2017-10-23)

The National Weather Service (NWS) 24 hour observed precipitation shows that there was 0 inches of rain in the Potomac basin above Little Falls. The NWS 3-day forecast predicts accumulations of 0.50 to 1.25 inches of rain over this same area. The NWS Global Ensemble Forecast System simulations predict that flow at Point of Rocks may rise above 2000 cfs, our trigger for daily drought monitoring, sometime this week.

Daily Flows:

Little Falls gage flow 2017-10-22: 1228 MGD (1900 cfs)

Daily Potomac flow and demand update (Sunday 2017-10-22)

No rain fell in the basin over the past 24 hours. The National Weather Service (NWS) 3-day forecast predicts accumulations of 0.5 to 1 inch of rain across the basin. The NWS 5-day forecast predicts accumulations of up to 1.75 inches of rain in the Potomac basin.

Daily Flows:

Little Falls gage flow 2017-10-21: 1280 MGD (1980 cfs)

Little Falls gage flow 2017-10-22: 1170 MGD (est., based on recently available real time data) (1810 cfs)

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

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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,