What is a sign that inversion might be lifting during a fire?

The indication that inversion might be lifting during a fire is smoke rising straight up. When a temperature inversion is present, it traps cooler air near the ground beneath a layer of warmer air, which prevents smoke and heat from rising effectively. If the inversion begins to lift, the smoke will no longer be confined and will rise vertically, signifying that the atmospheric conditions are changing and that the fire may receive more oxygen and more favorable burning conditions.

In contrast, thick layers of fog typically suggest that moisture may be present in the air, which can also be associated with stable atmospheric conditions and not necessarily indicate a lifting inversion. Heavy rainfall can suppress fire activity and would not typically be associated with inversion lifting. Steady winds from one direction can affect fire behavior but do not directly indicate changes in the presence or lifting of an inversion layer.