# What is an Operational Forecast System?

![hourly forecast of water levels for Chesapeake Bay](/facts/ofs.jpg "hourly forecast of water levels for Chesapeake Bay")

_These maps show typical hourly forecasts of different oceanographic conditions for Chesapeake Bay. Similar hourly spatial animations for the next 48 hours are available [online](https://tidesandcurrents.noaa.gov/models.html) for other locations and are updated every six hours._

An Operational Forecast System (OFS) provides a nowcast and forecast (up to 120 hours) of water levels, currents, salinity, water temperatures, and winds for a given area. These systems are located in coastal waters around the nation and the Great Lakes in critical ports, harbors, and estuaries.

Nowcasts and forecasts are scientific predictions about the present and future states of oceanographic and meteorological parameters within coastal regions. A nowcast covers the past 24 hours to the present and provides model output for locations where observational data are not available. A forecast provides information from the present time up to 48 hours out and these are updated every six hours. Nowcasts and forecasts are generated from NOAA real-time and forecast conditions.

Activities in which winds, water levels, currents, water temperature, or salinity are important may benefit from the information provided by an operational forecast system. These versatile systems can be used for everything from search and rescue to recreational boating and fishing to storm effect tracking.

Operational Forecast Systems are operated and maintained by NOAA’s [Center for Operational Oceanographic Products and Services](https://tidesandcurrents.noaa.gov/).

## **Operational Forecast System vs. NOAA Tide Tables**

For decades, mariners in the U.S. have depended on NOAA’s Tide Tables for the best estimate of expected water levels and tidal currents. These tables provide accurate predictions of the astronomical tide and tidal currents (i.e., the change in water level and current due to the gravitational effects of the moon and sun and rotation of the Earth). However, they cannot predict localized water level changes and variations in currents due to wind, atmospheric pressure, and river flow, which are often significant. As a result, OFS were established to provide water level, current, temperature, wind and salinity nowcasts and forecast guidance based on real-time observation data, meteorological forecasts, and astronomical predictions.

Did you know? - *In August, 2019, NOAA launched two new [Operational Forecast Systems](https://tidesandcurrents.noaa.gov/news/new_oceanographic_forecast_models_will_aid_mariners.html): one for the Great Lakes (Lake Huron and Lake Michigan) and one in Cook Inlet, Alaska. These models will help mariners to navigate their local waters safely and more efficiently, providing operational nowcast and forecast guidance (out to 48 hours for Cook Inlet, and 120 hours for the Great Lakes) on parameters such as water levels, water temperature, salinity, and currents.*

- [NOAA Operational Forecast System](https://tidesandcurrents.noaa.gov/models.html)

- [Center for Operational Oceanographic Products and Services](https://tidesandcurrents.noaa.gov/)

- [Office of Coast Survey](https://www.nauticalcharts.noaa.gov/ )

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