The Great Lakes Operational Forecast System (GLOFS)

Table of Contents

  1. Background
  2. About the Products
  3. About the Production Schedule
  4. About the Hydrodynamic Model
  5. About the Inputs Used by the Nowcast Guidance Cycles
  6. About the Inputs Used by the Forecast Guidance Cycles
  7. About Quality Control of CO-OPS Real-time Products
  8. About Partnerships and Collaborations
  9. Disclaimer

The Great Lakes Operational Forecast System (GLOFS) is a NOAA automated model-based prediction system aimed at providing improved predictions (guidance) of water levels, water currents and water temperatures in the 5 Great Lakes (Erie, Michigan, Superior, Huron and Ontario) for the commercial, recreation, and emergency response communities. GLOFS generates hourly nowcast guidance (analyses) and four times daily forecast guidance (out to 30 hours) of total water level, current speed and direction, and water temperature for each of the Great Lakes. The GLOFS predictions will enable users to increase the margin of safety and maximize the efficiency of commerce throughout the Great Lakes.

About the Products
GLOFS produces automated, numerical model-generated nowcast guidance (analyses) of present physical conditions and forecast guidance of future conditions or each of the Great Lakes. GLOFS predictions included in the nowcast and forecast guidance include water levels, water currents, and water temperature. The GLOFS nowcast and forecast guidance is available to users in several forms including graphical products and NetCDF files. The graphical products include 1) time series that depict the most recent nowcast and forecast guidance at a specific station along with the latest observations and 2) map animations that depict an aerial view of a particular variable across the lakes. The water level output from the numerical model used by GLOFS is adjusted to be relative to the low water datums of the International Great Lakes Datum, 1985 (IGLD 1985). In addition, in order to take into account seasonal changes in water level, a 7 day mean is calculated for each lake from observed water levels from NOAA's National Ocean Service's (NOS) National Water Level Observation Network (NWLON). This mean value is added along with the IGLD to the model's water level predictions to obtain the predicted total water level which is displayed on the time series plots.

The NetCDF files include GLOFS output at selected observing sites and for each entire lake. The NetCDF files can be accessed from the CO-OPS OPeNDAP web sever at

About the Production Schedule
GLOFS uses a separate configuration of the POM model for each lake. These models are run independently at slightly staggered times (see Table). The nowcast guidance cycles are run hourly for each model. The forecast guidance cycles are run 4 times a day (every 6 hours), with initial conditions at 0000, 0600, 1200, and 1800 UTC. The later launch times for 4 of the 5 lakes are done in order to include late arriving observations from Canadian fixed buoys.

Lake Hourly Nowcast Launch Time
(minutes past top of the hour)
Four/Day Forecast Guidance Launch Time
(minutes past 00, 06, 12, or 18 UTC)
Erie 50 50
Michigan 33 33
Ontario 56 56
Huron 62 62
Superior 67 67

About the Hydrodynamic Model
GLOFS uses as its hydrodynamic model, a version of the Princeton Ocean Model (POM), a sigma coordinate (vertical), curvilinear coordinate (horizontal), free surface, ocean model, which includes a turbulence sub-model. POM was developed in the late 1970's by Dr. Alan Blumberg and Dr. George Mellor, with subsequent contributions from numerous other researchers. The model has been used for modeling of estuaries, coastal regions, basin and global oceans. The present version of POM used by GLOFS has been adapted to the Great Lakes in work led by Dr. David Schwab at NOAA's Great Lakes Environmental Research Laboratory (GLERL) and researchers at The Ohio State University.

Separate POM models are run independently for each lake. Each particular lake model has the same hydrodynamic model, but varies uniquely in grid dimensions, grid cell size, and sigma layers (see table below).

Lake Grid Dimensions
Cell Size
Sigma layers
Erie 81 x 24 5 11
Michigan 53 x 102 5 20
Ontario 61 x 25 5 20
Huron 81 x 75 5 20
Superior 61 x 30 10 20

About the Inputs Used by the Nowcast Guidance Cycles
The hourly nowcast guidance cycles of GLOFS use surface meteorological data from a wide variety of observing platforms on and around the lakes. The different observing platforms include airway stations at airports, Coastal-Marine Automated Network (C- MAN) stations, NOAA/GLERL's mesonet stations, NOS' NWLON stations, and U.S. and Canadian fixed meteorological buoys. The real-time observations are provided courtesy of the National Weather Service's National Centers for Environmental Prediction (NCEP). Data used from these stations includes surface wind speed and direction, cloud cover, air temperature, dew point temperature and surface water temperature, if available. Wind observations taken at heights greater than 33 ft (10 meters) are adjusted to 33 ft based on the stability of the atmosphere over the lakes, then spatially interpolated to the hydrodynamic model grids on one hour increments.

Lake wide surface water temperatures for each Great Lake are obtained daily from NOAA's Coastwatch Great Lakes Surface Environmental Analysis (GLSEA). The GLSEA lake surface water temperature analysis is generated daily based on data from the AVHRR sensor on board NOAA's polar orbiting satellites. The daily lake-wide surface water temperature data is used in the computation of the stability of the atmosphere over the lakes.

About the Inputs Used by Forecast Guidance Cycles
The four times per day forecast guidance cycles of GLOFS are forced by surface wind (10 m above ground level) and surface air temperature (2 m above ground level) forecast guidance from the National Weather Service's operational North American Mesoscale (NAM) weather forecast model. The original spatial and temporal resolutions of the NAM forecast guidance is 7.5 miles (12 km) and 3 hours, respectively. The NAM forecast guidance is interpolated to the grid resolution of the POM grid for each lake and time resolution of 1 hour intervals.  These interpolated surface wind and air temperature fields are used by GLOFS' hydrodynamic models to generate oceanographic forecast guidance for each lake out to 30 hours. The forecast guidance cycle of GLOFS does not use or calculate surface heat flux from NAM output.

About Quality Control of CO-OPS Real-time Products
All CO-OPS official real-time products, including forecast guidance from the Ocean Service's Operational Forecast System for the Great Lakes and estuaries are monitored by the CO-OPS's Continuous Operational Real-Time Monitoring System (CORMS). CORMS provides data communications, data analysis, system monitoring and notification support to a variety of users, using input from real-time tide, current, water level, other marine environmental sensors, and forecast guidance model systems, which are deployed nationwide in many U.S. ports and waterways.

CORMS provides 24 hour a day, 365 days a year monitoring and quality control of sensors and data in order to insure the availability, accuracy, and quality of tide, water level, current, and other marine environmental information. CORMS is intended to identify invalid and erroneous data and information before application of the data by real-time and near real-time users. The CORMS is monitored by teams of technicians in the Silver Spring, Maryland offices of NOAA.

About Partnerships and Collaborations
The success of the Great Lakes Operational Forecast System (GLOFS) is a result of partnerships across numerous NOAA offices and The Ohio State University.

GLOFS is based on the Great Lakes Forecasting System (GLFS) developed by The Ohio State University (OSU) and NOAA's Great Lakes Environmental Research Laboratory (GLERL) in the late 1980's and 1990's under the direction of Dr. Keith Bedford (OSU) and Dr. David Schwab (GLERL). GLFS involved over a dozen OSU graduate students, research assistants and post doctoral researchers at GLERL and OSU, and other OSU faculty members. The development of GLOFS was funded by over 36 contracts from 25 different sources. The first routine nowcast for Lake Erie began at OSU in 1992. GLFS was recognized with an award in 2001 by the American Meteorological Society as the first U.S. coastal forecast guidance system to make routine real‑time predictions of currents, temperatures, and key trace constituents.

A workstation version of GLFS called The Great Lakes Coastal Forecast System (GLCFS) has been running in semi-operational mode at GLERL for Lake Erie starting in Feb. 1997 and for all 5 Great Lakes since 2002. GLCFS generated nowcast guidance 4 times per day and forecast guidance out to 60 hours twice per day. GLERL made output from GLFS available to NOAA's Weather Forecast Offices in the region.

The transition of the Great Lakes prediction system to operations at NOAA's National Ocean Service was a joint effort between NOAA's GLERL, CO-OPS and Coast Survey Development Lab, private industry (, and academia (OSU).

Access to critical near-real-time observational data and forecast guidance inputs has been made possible by Mr. David Michaud and others at NOAA's National Centers for Environmental Prediction (NCEP) and Mr. Greg Lang at GLERL.

GLOFS is maintained in an operational environment 24 hours a day, 365 days a year, by NOAA's Center for Operational Oceanographic Products and Services (CO-OPS).

Nature of GLOFS Products
The Great Lakes Operational Forecast System (GLOFS) has been implemented by NOAA's National Ocean Service (NOS) to provide the maritime community with improved short-term predictions of water levels, water currents and water temperatures of the Great Lakes. GLOFS uses a numerical hydrodynamic model to generate these predictions. Therefore, these predictions should be considered as computer-generated nowcast and forecast guidance. For more detailed information related to the OFS disclaimer, please visit at the Disclaimers web page.
Use of Data and Products
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