Merrimack River at Nashua
Future / Actual / Minor
OWP 2.0 WWA Modal Title
01/11/2021, 10:04 PM UTC through 01/11/2021, 10:04 PM UTC
Sender
Sent
- Warning: no valid ratings curve available. Transformations to and from FEET/CFS/KCFS will not happen.
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Observed (OBS) 06/16/2025 4:15 AM EDTOfficial Forecast (FCST) 06/15/2025 12:29 PM EDTRecord: 41.3 ftCATEGORY STAGE 
Major Flooding 35 ft Moderate Flooding 26 ft Minor Flooding 18 ft Action 16 ft Reliability of the Forecast: Based on current and forecast river, weather and reservoir conditions
NOTE: Forecasts are issued routinely year-round.
National Water Model Hydrograph
Official NWS streamflow forecasts are produced by NWS hydrologic forecasters for river gauge locations using hydrologic models which are calibrated to that location. This process considers additional guidance and information, including local expertise and experience, to produce the best forecast possible. The NWM output provides supplemental guidance to NWS forecasters and should not be considered an official NWS river forecast.
Flood Impacts
- 40 - This is a disastrous...life threatening flood. This compares to the Great New England Flood of 1936. Follow the advice of local officials...and evacuate if told to do so.
- 35 - This is a major...life threatening flood event. The river has not reached this height since the Great New England flood of 1936. Major flooding will affect the communities of Merrimack and Litchfield through Nashua and Hudson. follow the advice of local officials...evacuate if told to do so. Stay away from the Merrimack River.
- 30 - This flood compares to the Hurricane of 1938 flood. This is a substantial flood event. Follow the directions of local officials...evacuate if told to do so. At this height the Merrimack River is moving very swiftly. Stay away from the river.
Gauge Info
| Coordinates | 42.7634, -71.4428 |
| RFC | NERFC |
| State | NH |
| WFO | GYX |
| County | Hillsborough |
| Data Provider(s) | |
| US Geological Survey | USGS--Water Resources of the United States |
| USGS | 01096508 |
Gauge Location
Recent Crests
| 1. | 18.81 ft | on 04-01-2010 |
| 2. | 23.50 ft | on 04-17-2007 |
| 3. | 12.50 ft | on 06-09-2006 |
| 4. | 26.00 ft | on 05-15-2006 |
| 5. | 14.00 ft | on 10-26-2005 |
Recent Crests
| 1. | 18.81 ft | on 04-01-2010 |
| 2. | 23.50 ft | on 04-17-2007 |
| 3. | 12.50 ft | on 06-09-2006 |
| 4. | 26.00 ft | on 05-15-2006 |
| 5. | 14.00 ft | on 10-26-2005 |
| 6. | 13.00 ft | on 10-10-2005 |
| 7. | 14.50 ft | on 04-02-2004 |
| 8. | 14.00 ft | on 04-01-2003 |
| 9. | 17.00 ft | on 06-17-1998 |
| 10. | 15.60 ft | on 04-20-1997 |
| 11. | 18.10 ft | on 10-22-1996 |
| 12. | 19.00 ft | on 04-18-1996 |
| 13. | 9.40 ft | on 11-15-1995 |
| 14. | 15.50 ft | on 04-13-1993 |
| 15. | 16.20 ft | on 04-01-1993 |
| 16. | 13.30 ft | on 04-29-1988 |
| 17. | 22.40 ft | on 04-07-1987 |
| 18. | 13.80 ft | on 04-22-1972 |
| 19. | 14.00 ft | on 02-12-1970 |
| 20. | 15.60 ft | on 04-23-1969 |
| 21. | 14.20 ft | on 03-28-1968 |
| 22. | 13.50 ft | on 04-05-1967 |
| 23. | 18.40 ft | on 03-28-1953 |
| 24. | 17.00 ft | on 04-04-1952 |
| 25. | 17.00 ft | on 04-04-1951 |
| 26. | 15.30 ft | on 03-23-1948 |
| 27. | 13.60 ft | on 03-22-1945 |
| 28. | 18.10 ft | on 04-14-1940 |
| 29. | 30.50 ft | on 09-23-1938 |
| 30. | 41.30 ft | on 03-20-1936 |
Historic Crests
| 1. | 41.30 ft | on 03-20-1936 |
| 2. | 30.50 ft | on 09-23-1938 |
| 3. | 26.00 ft | on 05-15-2006 |
| 4. | 23.50 ft | on 04-17-2007 |
| 5. | 22.40 ft | on 04-07-1987 |
Historic Crests
| 1. | 41.30 ft | on 03-20-1936 |
| 2. | 30.50 ft | on 09-23-1938 |
| 3. | 26.00 ft | on 05-15-2006 |
| 4. | 23.50 ft | on 04-17-2007 |
| 5. | 22.40 ft | on 04-07-1987 |
| 6. | 19.00 ft | on 04-18-1996 |
| 7. | 18.81 ft | on 04-01-2010 |
| 8. | 18.40 ft | on 03-28-1953 |
| 9. | 18.10 ft | on 10-22-1996 |
| 10. | 18.10 ft | on 04-14-1940 |
| 11. | 17.00 ft | on 06-17-1998 |
| 12. | 17.00 ft | on 04-04-1951 |
| 13. | 17.00 ft | on 04-04-1952 |
| 14. | 16.20 ft | on 04-01-1993 |
| 15. | 15.60 ft | on 04-23-1969 |
| 16. | 15.60 ft | on 04-20-1997 |
| 17. | 15.50 ft | on 04-13-1993 |
| 18. | 15.30 ft | on 03-23-1948 |
| 19. | 14.50 ft | on 04-02-2004 |
| 20. | 14.20 ft | on 03-28-1968 |
| 21. | 14.00 ft | on 02-12-1970 |
| 22. | 14.00 ft | on 04-01-2003 |
| 23. | 14.00 ft | on 10-26-2005 |
| 24. | 13.80 ft | on 04-22-1972 |
| 25. | 13.60 ft | on 03-22-1945 |
| 26. | 13.50 ft | on 04-05-1967 |
| 27. | 13.30 ft | on 04-29-1988 |
| 28. | 13.00 ft | on 10-10-2005 |
| 29. | 12.50 ft | on 06-09-2006 |
| 30. | 9.40 ft | on 11-15-1995 |
Vertical Datum Table
| type | NAVD88 |
|---|---|
| major Flooding | 121.96 ft |
| moderate Flooding | 112.96 ft |
| minor Flooding | 104.96 ft |
| action | 102.96 ft |
| Latest Value | 92.76 ft |
| Gauge Zero | 86.96 ft |
Probability Information
No Images Available
Unique Local Info
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Potential River Levels Used to Estimate the Chance of Flooding and the Range of Possible River Levels |
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| 10 Day (HEFS) | 7 Day (NAEFS) | 7 Day (GEFS) |
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Note: Use the official hydrograph at the top of this web page for river levels within the next 72 hours.
See the Product Description Document link for more details on the interpretation of the 3,7 day graphics.
Click individual graphics to enlarge.
Collaborative Agencies
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.