The Category Day is determined by the ventilation rate, which is the afternoon mixing height in meters, times the transport windspeed in meters per second.  Forestry burning activities should proceed according to the table below:





 < 2,000

No Burning!


 2,000 - 4,000

No burning until 11:00 am and not before surface inversion has lifted. Fire out by 4:00 pm.


 4,000 - 8,000

Daytime burning only after inversion has lifted.


 8,000 - 16,000

Burning anytime.
Night burns use backing fires with surface wind speeds greater than 4 mph.


> 16,000

"Unstable" and windy.
Excellent smoke dispersal.
Burn with caution!

You can obtain a Fireweather forecast, including Category Day, from the Weather Service.