ANGSTROM INDEX

LOW
>4.0
MODERATE
4.0 - 2.5
HIGH
2.5 - 2.0
EKSTREME
<2.0

The Angtstrom Index (Angstrom) is used primarily in Sweden, it uses the air temperature and relative humidity to calculate a numerical index of fire danger. That number is then equated to the Fire Danger severity of either Extreme, High, Moderate, or Low. It's based solely on weather conditions, with no adjustment for fuel moisture. The lower the number, the higher the fire risk.

Angstrom Index = (H/ 20)+ ((27-T) /10)
where:
H = Relative Humidity as % (0-100)
T = Temperature in Degrees Celcius.

> 4.0 Fire occurrence unlikely
4.0 – 2.5 Fire conditions unfavourable
2.5 – 2.0 Fire conditions favourable
< 2.0 Fire occurrence very likely