NWS Sioux Falls Fire Danger Categories

EXPLANATION OF WHAT TO EXPECT IN REGARD TO BURNING CONDITIONS FOR THE FIVE CATEGORIES OF THE GRASSLAND FIRE DANGER INDEX AND RED FLAG WARNING

LOW: Low ignition hazard. Dead fuels do not ignite readily from any source.

MODERATE: Medium ignition hazard of dead, fine fuels such as cured grass. Fires can start from accidental causes such as campfires but the number of starts is relatively low. Fires are not likely to become serious and control is relatively easy.

HIGH: Moderately high ignition hazard of dead, fine fuels such as cured grass. Fires can start from most accidental causes. This category denotes "easy" burning conditions, with matches and campfires becoming dangerous. In fact, unattended campfires are likely to escape. On windy days, fires in cured grasslands can burn briskly with moderate rates of spread. However high intensity fires are usually limited unless the fire spreads into a heavy concentration load of cured grass. Fires can be easily contained if hit fast and early in the burn.

VERY HIGH: High ignition hazard with matches and campfires dangerous. All cured grasslands ignite readily and, immediately after ignition, spread rapidly. Fires will likely become hot enough to ignite live, fine fuels (one-quarter inch or less in diameter) by pre-heating. Short range spot fires are a danger. Fires burning in cured, tall grassy fuels, sawgrass or cattails could develop high intensity characteristics. Fire containment at the head of the fire becomes difficult until the fire environment changes.  A very high grassland fire danger statement will always be issued in these circumstances.

EXTREME and RED FLAG: For NWS Sioux Falls, these two categories are generally the same thing, just two different products to maximize dissemination to both the public and government agencies.  In cured grasslands, expect a quick ignition, extreme rate of spread and aggressive burning.  Fires will be hot enough to ignite live fuels three inches or less in diameter.  Extreme fire behavior is probable if fires reach cured, tall grassy fuels, sawgrass or cattails with short to intermediate range spot fires likely.  All fires are serious.  Fire intensity is usually high enough that burning of woody fuels with diameters of three inches or less in tree stands is likely.  Direct attack on the fire is rarely possible until the fire environment changes.  Fire fighting on the flanks is possible.  Sioux Falls will issue a Red Flag Warning when wind speeds between the sustained wind and gusts are averaging around 25 mph, coupled with humidity values that are less than or equal to 25 percent.  The one exception is our south central South Dakota zones where the humidity has to be less than or equal to 20 percent.  In these instances, goverment agencies can use the red flag warning to make decisions.  As an added service, the public and more localized government agencies can use the accompanying extreme grassland fire danger statement to also aid in decision making.