Weather instruments are critical to the conduct of all prescribed fires. Weather kits should be equipped with a psychrometer (temperature & relative humidity), anemometer (wind speed), bottle of water, note pad, and compass (Kit 1). Improvements in fire weather kits include a digital readout hygrometer that gives quick relative humidity and temperature in Fahrenheit or centigrade, and a hand-held wind indicator that uses a wind-driven fan (Kit 2) as opposed to the “pith ball” type.
Burning is very weather sensitive. In addition to National Weather Bureau forecasts, on-site measurements are critical and should be taken prior to and during the burning activity. Data should be recorded at regular intervals, usually every 30 minutes. Wind speed affects fire behavior immediately. A change in relative humidity does not affect moisture levels in fine fuels for about 30 minutes.