You probably know that a correlation is the relationship between two sets of variables used to describe or predict information. Therefore, the correlation coefficient is the degree in which the change in a set of variables is related.
Delta G is a measure of the net effect of these two concepts, and will help you predict whether or not a reaction will actually take place! Delta G naught refers to the Delta G if you were creating a given compound from its pure elemental form at standard temperature and pressure. So it's how likely a compound would form from its individual elemental components!
An example of a forecast product from the GFS, in this case a 96-hour forecast of 850 mb geopotential height and temperature. The Global Forecast System (GFS) is a global numerical weather prediction system containing a global computer model and variational analysis run by the United States' National Weather Service (NWS). The mathematical model is run four times a day, and produces forecasts for up to 16 days in advance, but with decreased spatial resolution after 10 days.