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Information on Research Based Monthly Forecasts

Current NOAA-GLERL AHPS Forecasts

These water level forecasts were produced by NOAA-GLERL's Advanced Hydrologic Prediction System (AHPS). Checking the 'Current Forecasts' box reveals the AHPS forecast for the next 10 months. The light blue bars indicate the 90% confidence interval for the forecasts. More information on the NOAA-GLERL AHPS model is below.

Archived AHPS Forecasts

The archived water level forecasts (produced by NOAA-GLERL's AHPS model) start in 1997. NOAA-GLERL's forecast probability bands for both 3-month (dark) and 6-month (light) forecasts can be shown on the dashboard by checking the appropriate menu boxes. The colored bands show the 90% probability intervals for the month's mean water level. If AHPS was always accurate, these bands would contain the observed water level 90% of the time. NOAA-GLERL recently started archiving AHPS' forecasts in order to assess its performance.

About the NOAA-GLERL AHPS seasonal forecast model

NOAA-GLERL's AHPS seasonal forecast model is a research tool, not associated with any operational decisions. However, it is relied on by many governmental agencies and others who need water level information for planning. The official seasonal water level forecast is a collaborative effort by the U.S. Army Corps of Engineers and Environment Canada. (see the current 6-month forecast)

AHPS is a physically-based model that combines historical meteorological data with a series of mathematical models and climate forecasts from NOAA's Climate Prediction Center to simulate multiple hydrologic variables (precipitation, runoff, evaporation). The net 'supply' of water to each basin is accounted for via virtual routing through the lakes and their connecting channels, leading to the predicted monthly levels. More information about NOAA-GLERL's water level forecasts and access to the daily updates can be found here. A recent study (Gronewold 2011) showed that the 90% probability band captures between 64 and 74% of the observed water levels, based on the years 1997 through 2009.


Croley, T., Lee, D., 1993. Evaluation of Great Lakes net basin supply forecasts. J. Am. Water Resources Association 29(2), 267-282

Croley, T., 1992. Long-term heat storage in the Great Lakes. Water Resources Research 28(1), 69-81.

Croley, T., Hartmann, H., 1985. Resolving Thiessen polygons. J. Hydrology 76(3-4),363-378