September brings the beginning of the fall fire weather season for eastern Iowa, northwestern Illinois, and extreme northeastern Missouri. The Fire Weather Forecast Zones (CHIFWFDVN) continue through November 30th, and will be issued twice a day around 4 am and 4 pm. The Grassland Fire Danger Index (GFDI) is a part of this product and is the primary driver of determining very high or extreme fire danger across the area, and the possible need of a Red Flag Warning (CHIRFWDVN). A Red Flag Warning is generally defined as a forecast warning to inform area firefighting and land management agencies that conditions will be ideal for wildland or cured cropland fire ignition and rapid propagation. After drought conditions, or when humidity is very low combined with high winds and abundant cured vegetation, the Red Flag Warning becomes a critical statement for state and firefighting agencies to steer their operations. To the public, a Red Flag Warning means extreme fire danger with increased probability of a quickly spreading vegetation fire in the area within 24 hours.
The extent of the fire danger and need of a Red Flag Warning are generally based on the type and amount of cured vegetation available, expected afternoon high temperatures, afternoon minimum relative humidity, and wind speed. Outdoor burning bans may also be proclaimed by local law and fire agencies based on Red Flag Warnings.
A separate but less imminent forecast of dangerous fire supportive conditions may include a Fire Weather Watch. This message is issued to alert fire and land management agencies, as well as the public, that the possibility that Red Flag conditions may exist beyond 12 hours of the issued forecast. The watch is issued generally 12 to 48 hours in advance of the expected conditions that may produce high fire danger. The watch then remains in effect until it expires, is canceled, or is upgraded to a Red Flag Warning.
Of course, dangerous fire potential this fall is highly dependent on precipitation amounts, frequency of precipitation occurrence, and cool moist conditions that may inhibit extreme fire behavior. Ambient dry to drought conditions have accelerated the vegetation drying and curing process for this time of year, and the threat of grass fires already exists in some locations when the appropriate weather conditions occur. When the GFDI-threat for grass fires is very high this fall, it will continue to be highlighted in the Hazardous Weather Outlook (HWO). The National Weather Service in the Quad Cities hopes that everybody has a safe and productive autumnal fire weather season.