Event (20) Convection column changes direction as it rises.
Air Observer or Field Observer
This photo shows a major smoke plume in the 2009 Black Saturday events. Up to around 2.5km AGL the smoke is moving right-to-left, above that it is moving left-to-right.
The inferrence is that the upper flow is in the pre-frontal continental air mass (NW), while the lower flow is in the post-frontal maritime air mass (SW).
While this particular event was expected, it clearly demonstrates a pattern that observers must watch for. The timing of arrival of wind changes has been a long-term concern and basis for research. However accurate wind change prediction may become, actual observations of the arrival remain critical for safety.
Event (20) Convection column changes direction as it rises.