Blue mold of tobacco ( Peronospora tabacina ) is a foliar fungus disease disseminated by tiny, microscopic spores in the atmosphere. the U.S. forecasting system located at N.C. University provides agricultural extension personnel, reseachers and other interested parties with timely information on the future movement of inoculum (spores) within the Southeast and mid-Atlantic states from known sources such as infested field, plant beds or greenhouses. Spore transport in the atmosphere uses the NOAA HY-SPLIT trajectory model. The trajectory model operates on the NOAA Nested Grid Model (NGM), a member of the family of numerical weather forecast models used nationally to predict 48-hour weather. Of primary interest are the atmospheric boundry layer and the forecast wind fields. The necessary NOAA weather data and trajectory model are provided by the U.S. Air Resource Laboratory, Silver Springs, Maryland. A trajectory plots the atmospheric pathway of a "packet" of air containing spores and calculates the temporal position(s) of spore clouds for the 48-hour period after a spore cloud leaves a source site or region. State Blue Mold coordinators report new and important continuing sources directly to the forecaster at MEAS, North Carolina State University via E-Mail. The geographic location of the disease is specified so grid coordinates can be assigned to each source. If a source ceases to exist, i.e. the field or greenhouse plants are destroyed, this information is reported as well. The forecaster generates a new set of trajectories each day.The blue mold forecast includes graphic figures (maps). A trajectory originates at a source and nodes represent six hour positions of the spore cloud. A Trajectory Climatology section describes the present and past weather conditions favorable for sporulation at the source including temperature, rainfall and cloud cover. Spores are deposited to earth by sedimentation and/or precipitation scavaging (rainout and washout). The weather associated with the trajectory path is given including protective cloud cover (related to UV radiation and dessication) and rain activity. A section on General Weather in the Southeast provides past, current and future weather events that influence the movement and risk of infection.