The Climate Forecast System (CFS) issues long term forecasts that can help make important decisions in regards to planting, applying herbicides, and harvesting. We hypothesized that the CFS forecasts thermal times are lower than observations because of a warming climate in Iowa. Observed maximum and minimum temperature data was obtained from NWS COOP stations. Thermal time was calculated for both the CFS forecasts and observations, and them were compared. For the three year period looked in this study, the statewide average for the CFS was 390 GDD, 15% less than observations. On average for August, the CFS was within 1% of observations. However, the CFS forecasted 115 GDD plus for the months of April and September. Studies have suggested that the climate in the Midwest region have been warming during the spring and autumn months, but remaining the same during the summer months; and this would agree with the results in this study.