Grade of cold air

Division of grade

General cold air

(6 ≤ Dt48 < 8) or (Dt48 ≥ 8 but Tmin>8 )

Strong cold air

Dt48 ≥ 8 and Tmin < 8

Cold wave

(Dt24 ≥ 8 or Dt48 ≥ 10 or Dt72 ≥ 12) and Tmin < 4

Strong cold wave

(Dt24 ≥ 10 or Dt48 ≥ 12 or Dt72 ≥ 14) and Tmin < 2

Extreme cold wave

(Dt24 ≥ 12 or Dt48 ≥ 14 or Dt72 ≥ 16) and Tmin < 0