Haines Index (also known as the Lower Atmosphere Severity Index) is a weather index developed by

meteorologist A meteorologist is a scientist who studies and works in the field of meteorology aiming to understand or predict Earth's atmosphere of Earth, atmospheric phenomena including the weather. Those who study meteorological phenomena are meteorologists ...

Donald Haines in 1988 that measures the potential for dry, unstable air to contribute to the development of large or erratic wildland fires. The index is derived from the stability (temperature difference between different levels of the atmosphere) and moisture content (

dew point depression The dew point depression (T-Td) is the difference between the temperature and dew point temperature at a certain height in the atmosphere. A lower dew point depression indicates that the air is more moist at a given temperature. For a constant te ...

) of the lower

atmosphere An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

. These data may be acquired with a

radiosonde A radiosonde is a battery-powered telemetry instrument carried into the atmosphere usually by a weather balloon that measures various atmospheric parameters and transmits them by radio to a ground receiver. Modern radiosondes measure or calculat ...

or simulated by a numerical weather prediction model. The index is calculated over three ranges of atmospheric pressure: low elevation (950-850 millibars (mb)), mid elevation (850-700 mb), and high elevation (700-500 mb). A Haines Index of 6 means a high potential for an existing fire to become large or exhibit erratic fire behavior, 5 means medium potential, 4 means low potential, and anything less than 4 means very low potential. The US National Weather Service discontinued use of the Haines Index along with Lightning Activity Level in its Fire Weather Forecasts in December 2024, citing new science that suggested these measures were not as effective as others in forecasting, according to Service Change Notice 24-107.

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