Preliminary heat index products are issued from the medium-range forecast function of the WPC for days 3 through 7 throughout the year. With the exception of day 3, these products are based on WPC MEDR forecasts. The day 3 forecast is based on the gridded Model Output Statistics (MOS) temperature and dew point temperature forecasts; while, forecasts for days 4 through 7 are based on the WPC medium-range forecast desk products. These are deterministic forecasts only.

       The early HI forecasts are made available primarily to facilitate the collaborative forecast process within the National Centers for Environmental Prediction. They also provide to other users of WPC forecasts an early look at heat index forecasts consistent with the early update of the web content found at the WPC Day 3--7 forecast site.

       Later in the day, beginning around 1840 UTC, the full suite of FINAL WPC heat index products becomes available during the warm season (May through September). That final suite of products includes probabilistic forecasts of minimum, mean, and maximum heat index exceeding certain thresholds. More information on the final suite of seasonal HI products is available as follows:
 

For more information on the generation of seaonal FINAL heat index products please click here.