The second number is how many hours in the last 24 that the station has hit Red Flag Criteria OR flirted with it. The first number is how many hours in the last 24 that the station has hit Red Flag Criteria. The "Duration" value contains two numbers. If the wind is within 5 mph and the humidity is within 5% of criteria, it is considered "Flirting" If the weather is hitting Red Flag criteria, but the fuel moisture is high, the fire growth risk is greately minimized.Ī "Flirting" station means that the observation is not hitting Red Flag criteria, but it is close. Other factors are important in assessing the fire growth and behavior risk, including the moisture in the live and dead vegetation (fuels). Red Flag conditions generally mean that the weather is favorable for dangerous fire growth and behavior. These criteria are locally set by the responsible NWS office, and vary by each office. The lowest the SI can be is 0.Ī "Red Flag" station means that the observation is hitting Red Flag criteria. Where: Wind = Highest speed between the sustained and gust. This is primarily intended to help filter the display of stations to only the weather significant ones, which is useful for networks with hundreds of stations. It is tuned such that it generally falls between 0 and 100, such that 30 is a typical number for a significant observation and 100 is about as bad as it gets. The severity index is an attempt to boil down the important fire weather parameters into a single value.
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