These data are the coordinated precipitation estimates as officially accepted by the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data. They are updated annually, approximately in October, by the National Ocean Service (NOS) office in Silver Spring, Maryland.
From the source data spreadsheet: Precipitation data reported below represent over-basin averages. These data were coordinated in 2010 with Environment Canada using data from 1900 through 2008.
From the source data spreadsheet: These Residual Net Basin Supplies data are not regularly coordinated with Canada. They were coordinated through 2008 to support the International Upper Great Lakes Study. These computations used actual month lengths when working with the change in storage values. Data is in m3/s. Lake Ontario was not included in the 2008 coordination.