It indicates, on average, if the forecasts are under predicted or over predicted. Values near 0 are best. It measures if two sets of data change together. Values close to 1 are best. Positive correlation indicates that large forecast values are associated with large observed values.
Negative correlation indicates that large forecast values are associated with large observed values.
No correlation occurs when values in both sets are unrelated. Higher numbers are better. Higher numbers are better. 1 indicate over-forecasting. The percent of times a forecast of high ozone did not actually occur.