The storm may be severe elsewhere but the mamma usually appear on the outflow side of the system under the anvil, away from the heavier precipitation. The rain core and its strong downdrafts cause a few peculiar lighting situations that can be deceiving. In the descending rain area, lower clouds are absent, causing this part of the sky to become relatively bright. Such a bright glow sometimes follows the gust front but precedes a heavy downpour. The sky can also display a greenish colour near the rain core or behind the gust front, but this is not related to tornadoes and represents no threat.
Dust plumes One last reminder about dust or dirt rising from distant fields.
Any strong wind gust will lift a cloud of dirt into the air and turbulent motions will mix it upward. If it is a microburst, the dirt will be concentrated, with a sharply defined forward edge and be angled forward. If it is a tornado debris cloud it will move more slowly, remain compact and symmetrical, and soon take the shape of a column. Without this discrete structure under the correct part of the storm, the event is more likely due to strong straight-line winds. The one exception is a dust devil, a column of whirling dust that looks like a mini-tornado but occurs exclusively on fair, dry days and is relatively harmless.