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Web Portal Changes: The Advanced Hydrologic Prediction Service (AHPS) hosted at will be replaced by the National Water Prediction Service (NWPS), with a target of Spring 2024. Existing AHPS content and features will be preserved and expanded within NWPS. The NWS is now accepting feedback on NWPS. Please visit for more information.

Experimental National Water Center Products: Flood Inundation Mapping services are now available for 10% of the U.S. population. Please visit for more information. The National Hydrologic Discussion, Area Hydrologic Discussion, Flood Hazard Outlook, and real-time geospatial services depicting River Forecast Center and National Water Model forecasts, continue to be accessible via the URL above, as described in the StoryMap here.

DID YOU KNOW... Please try our new TEST hydrograph page link at: - Just replace “abcde” with your local hydrograph five character ID found in the lower left corner of the hydrograph.  In late March of 2024, the base URL path will become  Feedback can be provided HERE

Hydrograph River at a Glance Download
Potomac River at Williamsport Stage (ft)Highest Observation: 2.07 ft at 6:00AM Nov 30, 2023Observed: 1.99 ft at 6:00AM Dec 01, 2023Observed: 1.96 ft at 6:00AM Dec 02, 2023Observed: 1.96 ft at 6:00AM Dec 03, 2023Observed: 1.94 ft at 6:00AM Dec 04, 2023City of HagerstownWLLM2(plotting HGIRZ) Graph Created (2:40AM Dec 5, 2023)ObservedLatest observed value: 1.94 ft at 6:00 AM EST 4-Dec-2023.
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About this graph
Tabular Data (UTC)
Tabular Data (EST)
XML Data
RSS Files
Datum: Not Available
NOTE: Gauge readings received once daily during low-water and more frequently during high water.

NOTE: Stage may be affected by ice.

NOTE: Graphical forecasts are not available for the Potomac River at Williamsport. During times of high water, forecast crest information can be found in the text products.

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Upstream Gauge - at Dam Number Five above Williamsport Upstream Gauge Downstream Gauge Downstream Gauge - at Shepherdstown
Flood Categories (in feet)
Not Available

Historic Crests
(1) 48.60 ft on 03/18/1936
(2) 37.00 ft on 04/27/1937
(3) 36.30 ft on 11/06/1985
(4) 36.10 ft on 10/16/1942
(5) 34.80 ft on 01/20/1996
Show More Historic Crests

(P): Preliminary values subject to further review.

Recent Crests
(1) 24.49 ft on 06/04/2018
(2) 22.90 ft on 05/19/2011
(3) 24.90 ft on 03/15/2010
(4) 31.10 ft on 09/08/1996
(5) 34.80 ft on 01/20/1996
Show More Recent Crests

(P): Preliminary values subject to further review.

Low Water Records
Currently none available.
Zoom Level:13
KML Image
Gauge LocationGauge Map Marker
Latitude/Longitude Disclaimer: The gauge location shown in the above map is the approximate location based on the latitude/longitude coordinates provided to the NWS by the gauge owner.
Flood Impacts & Photos Collapse
If you notice any errors in the below information, please contact our Webmaster
62 Water begins to flood the R.C. Wilson water treatment plant. The plant will flood at a lower level if the levee protection is breached.
32 Water enters the Williamsport Cushwa visitor center and trolley building in Williamsport.
29 Water covers most of the C&O Canal towpath and the bridge over the Conococheague Aqueduct.
28 Water begins to cover the C&O Canal Towpath.
25 Structures begin to flood at the Potomac Fish and Game Club.
23 Water begins to inundate lower portions of the Potomac Fish & Game Club.
10.5 Water exceeds the banks and covers the road at the end of the boat ramp in Williamsport.
About This Location Collapse

Latitude: 39.609167° N, Longitude: 77.847500° W, Horizontal Datum: NAD83/WGS84

River Stage
Reference Frame
Gauge Height Flood Stage Uses
NWS stage 0 ft Not Available Interpreting hydrographs and NWS watch, warnings, and forecasts, and inundation maps
Vertical Datum Elevation
(gauge height = 0)
(gauge height = flood stage)
Elevation information source
NAVD88 Not Available Not Available Survey grade GPS equipment, FEMA flood plain maps, newer USGS topographic maps
NGVD 29 327.7 ft 350.7 ft Older USGS topographic maps, NGVD29 benchmarks
MSL Not Available Not Available Older USGS topographic maps, MSL benchmarks
Other Not Available Not Available  
Additional Information Collapse
NWS Watch and Warning services were moved from this location to Dam Number Five on December 11th, 2019. Forecasts and warnings for the Williamsport area are now based on the Dam Number Five location.
Resources Collapse
Hydrologic Resources Additional Resources
Collaborative Agencies Collapse
The National Weather Service prepares its forecasts and other services in collaboration with agencies like the US Geological Survey, US Bureau of Reclamation, US Army Corps of Engineers, Natural Resource Conservation Service, National Park Service, ALERT Users Group, Bureau of Indian Affairs, and many state and local emergency managers across the country. For details, please click here.
NWS Information
National Weather Service
(Baltimore/Washington) Sterling Weather Forecast Office
43858 Weather Service Rd.
Sterling, VA 20166
(571) 888-3500
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Page last modified: 2-Nov-2020 7:30 PM
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