From Homepage:

The “official” temperature forecasts (outlooks) are issued on the 15th of the month preceding the target forecast month (0.5-month lead time). These forecasts are stored in the Archive for verification. Monthly forecasts with the lead time of up to 10.5 months are available for subscribers in the form of 1) maps showing the probability of occurrence of above and below normal temperature over the contiguous United States and 2) time series of normalized temperature anomalies for selected cities. Currently the forecasts of monthly temperature anomalies, as well as heating degree days (HDDs) and cooling degree days (CDDs) are prepared for Atlanta, Dallas, Chicago, Cincinnati, Minneapolis and New York. Learn more about the forecasts. Try one month of our service for a nominal fee of $1.

From About:

The forecasts are prepared by the 15th of each month with the lead time from 0.5 month to 10.5 months (a total of 11 forecasts). Those forecasts are available for subscribers only. By the end of each month, the forecast for the next month may be adjusted (zero lead time), after which it becomes public.