Driving up the Pacific Highway north out of Sydney this morning, I was intrigued to see a pyrocumulus forming above a hazard reduction burn near Hornsby.
During the Southern hemisphere winter, the rural fire services carry out controlled burns to reduce the fuel supply for the forthcoming bushfire season.
The remainder of the sky was clear, with only a few upper altitude stratiform clouds, but there was a distinct cumuliform top to the column of smoke rising from the fire. The updraft generated by the fire is sufficient to cause a rising column of air, and the conditions were such that adiabatic expansion allowed the air to cool below the dew point. The cloud had dissipated within ten minutes.
Very nice! Link to location map.