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Column Definitions for the FCAMMS Point Forecast Product
The national FCAMMS Point Forecast Product generates a Smoke Dispersion Forecast Guidance table that predicts conditions at your location affecting fire and smoke.
The table contains several columns to help you understand the information.
- Mixing Height. The depth of the atmospheric layer where turbulent mixing causes momentum, moisture, and other properties to be more or less uniform. High values indicate more rapid smoke dispersion and greater risk of gusty, turbulent winds. They can also indicate a greater chance of wind and moisture conditions aloft coming to the ground, which can influence fire behavior.
- Transport wind speed and direction: Transport wind is defined as the wind that determines the direction and speed with which smoke is transported away from its source. In these maps, this is the average speed and direction of the winds from the ground to the mixing height. Note that some state or local agencies calculate transport winds differently, but the convention used here is the most common.
- Ventilation index: The mathematical product of the Mixing Height and the Transport Wind. This provides an estimate of how high and how far smoke (or other pollutants) will disperse: a high ventilation rate suggests that smoke will spread out quickly and through a deep layer of the atmosphere, so that surface concentrations downwind will be lower than they would be with a lower ventilation rate.
PM2.5 ground concentrations: PM2.5 stands for particulate matter <= 2.5 microns. In practical terms, this is the fine-scale component of aerosol particulates, and ambient levels are regulated under the U.S. EPA National Ambient Air Quality Standards (NAAQS) (the current standard is a 24-hour average of < 35 ug/m^3). Wildland fire produces PM2.5 (along with larger sizes), and can contribute to NAAQS exceedances when smoke becomes heavy in an area.
Forecasts of PM2.5 must be taken in context as modeled PM2.5 levels are dependent on a chain of models (fire consumption, emissions, plume injection, and dispersion). Additionally, wildland fire smoke models often omit other (non-fire) sources than can raise the observed level in a region. Often it is best to view PM2.5 levels in context of previous forecast values.
- Haines index (low, medium, and hight): A simple measure of the probability that an existing fire will become a dangerous, erratic fire in the absence of strong surface winds. It reflects atmospheric stability and moisture in a layer of the atmosphere roughly 1 to 5 km above the surface. High values indicate high risk of dangerous behavior.
The Haines Index is calculated across three pressure layers, Low (950-850 mb), Middle (850-750 mb), and High (750-500 mb) based on the surface elevation at the location of interest. In general terms, the Low variant is appropriate for locations below 200 m elevation, the Middle variant is for locations between 200 m and 1000 m, and the High variant for locations above 1000 m elevation.
A Haines Index value of 2 or 3 is considered “Very Low;” 4 is “Low;” 5 is “Moderate;” 6 is “High.”
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