Great Lakes About Great Lakes Trolling
Great Lakes Trolling puts NOAA's forecasts for the five Great Lakes on one fast, full-screen map: water temperature at any depth, the thermocline, currents, and waves, with measured readings from buoys and shore stations alongside. It is free, needs no account, and works on phones and computers.
It was built for anglers, boaters, and anyone curious about what is happening under the surface. NOAA publishes this data openly, but in formats meant for scientists. This site downloads it, turns it into map layers, and keeps them current.
Where the data comes from
| Source | Used for | How often it updates |
|---|---|---|
| NOAA Great Lakes Operational Forecast System (GLOFS)National Ocean Service, Center for Operational Oceanographic Products and Services | Water temperature at every depth, the thermocline, and currents. One model per lake: Superior (LSOFS), Michigan and Huron (LMHOFS), Erie (LEOFS), and Ontario (LOOFS). | Four runs a day, at 00, 06, 12, and 18 UTC, each forecasting 120 hours ahead. A run is published about 2.5 to 3.5 hours after it starts. |
| NWS Great Lakes Wave model (GLWU)National Weather Service, National Centers for Environmental Prediction | Significant wave height, wave period, and the direction waves come from. | Every hour, forecasting 48 hours ahead. Most runs are published a few minutes after the hour; the 01, 07, 13, and 19 UTC runs about 35 minutes after. |
| NOAA National Data Buoy Center (NDBC) | Measured water temperature, waves, and current-meter readings from buoys and shore stations. | As stations report, typically every 10 to 60 minutes. Readings more than 6 hours old are hidden. Many buoys are taken out of the water for the winter. |
| Great Lakes bathymetryEsri Canada, with NOAA's lake-model depths | The water depth shown when you click the map. | Updated rarely, only when new surveys are conducted. Where the contours do not reach, depth comes from the lake model. |
| BasemapsCARTO, OpenStreetMap contributors, and Esri | The map underneath the data layers: dark, standard, and satellite. | Maintained by each provider. |
Accuracy and limitations
- Temperatures, currents, and waves are computer model forecasts, not measurements. They are usually close, but can be off, especially near shore, in bays and harbours, and right after storms.
- The thermocline is a band. Its top, the depth on the map, is where the warm surface layer of fairly even temperature ends and the water starts to cool; its bottom is where the cooling eases off again, and the water-column view shows both and the thickness. It only counts if that warm layer is at least 10 ft thick and the water below it cools at least three times faster, so a sharp bend in the temperature curve counts even when the top layer is cooling slowly, but water that cools at a steady rate does not. NOAA's models store temperatures at fixed depths, a few metres apart near the surface and further apart below, so both are estimates between those levels. Water without one (mixed in fall turnover and winter, or cooling gradually from the surface down) is left clear, so the map shows through.
- Buoy and station readings are real measurements, but only at one spot each, and are shown as reported.
- Past 30 days shows the conditions the map showed as "Now" at each hour, saved as they happened: the models' best estimate at the time, not forecasts. Past hours show the surface; water-column profiles are saved every 3 hours, and the record starts when the site began saving it.
- Not for navigation. Always check official NOAA forecasts, marine warnings, and nautical charts before going out on the water.