According to Middle Atlantic River Forecast Center predictions, no rain is expected for the next 24 hours. Forecasts suggest an average basin rainfall of around 0.15 inches over the next three days and 0.83 inches over the next week.
The proactive voluntary load shift from Great Falls to Little Falls by Washington Aqueduct is still ongoing.
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 multisensor precipitation estimates)
Yesterday's area-weighted average basin precipitation: 0 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.19 (inches)
Daily flows:
Little Falls gage flow 2023-09-04: 419 MGD (648 cfs)
Little Falls gage flow 2023-09-05: 409 MGD (est., based on recently available real-time data) (633 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-09-04: 711 MGD (1100 cfs)
Point of Rocks flow 2023-09-05: 704 MGD (est., based on recently available real-time data) (1090 cfs)
Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-09-04):
Fairfax Water Corbalis withdrawal - Potomac: 137 MGD
WSSC Water Potomac withdrawal: 141 MGD
Washington Aqueduct withdrawal - Great Falls: 87 MGD
Washington Aqueduct withdrawal - Little Falls: 62 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 4 MGD
Total Potomac withdrawal: 433 MGD
Total net Potomac withdrawal: 429 MGD
Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2023-09-04):
FW Occoquan withdrawal: 77 MGD
WSSC Patuxent withdrawal: 60 MGD
Yesterday's total system withdrawal (2023-09-04): 564 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1100 cfs
QPR, obs: 1100 cfs
QPR, WS: 0 cfs
Note to Loudoun Water: See NWS ensemble flow forecasts (HEFS, GEFS, NAEFS) for Point of Rocks flow for the next 7 days – see https://www.weather.gov/erh/mmefs_marfc?id=PORM2&model=NAEFS.
Recommended operations for today (2023-09-05 A.M.):
Fairfax Water:
Keep Potomac withdrawals as steady as possible.
WSSC:
Keep Potomac withdrawals as steady as possible.
Aqueduct:
Keep Little Falls withdrawals as steady as possible. Great Falls per operational preference.
Reservoirs - Usable storage for yesterday (2023-09-04, BG):
Facility, %Full, Current, Usable Capacity*
WSSC’s Patuxent reservoirs, 48%, 5.05, 10.53
Fairfax Water’s Occoquan reservoir, 95%, 7.75, 8.17
Little Seneca Reservoir, 97%, 3.76, 3.87
Jennings Randolph Total Reservoir, 77%, 22.61, 29.4
Jennings Randolph water supply**, 100%, 13.1, 13.1
Jennings Randolph water quality**, 58%, 9.51, 16.3
Savage Reservoir, 57%, 3.62, 6.33
*Storage and capacities for Occoquan, Patuxent and Little Seneca reservoirs are provided by Washington metropolitan area water utilities, and based on best available information. Storage and capacities for Jennings Randolph and Savage reservoirs are based on observed water levels and available US ACE water level/storage tables from 1998. ICPRB estimates that sedimentation has resulted in a loss of total available storage in Jennings Randolph Reservoir of 1.6 BG in recent years, and this loss is not reflected in the numbers above.
** ICPRB's initial estimate. Final accounting of Jennings Randolph water supply versus water quality storage will be provided at a later date by the US ACE.