Pink and orange clouds appeared in the sky above Falkirk on Thursday evening.
The anthropogenic, or artificial, clouds were captured in photographs taken around Forth Valley by BBC Scotland News website readers and BBC WeatherWatchers.
The clouds are believed to have come from the Ineos petrochemical plant in Grangemouth.
A spokesman for Ineos said "the clouds of water vapour most likely emanated from our cooling towers".
Analysis by Kawser Quamer, BBC Scotland Weather
These are 'artificial' or anthropogenic cumulus clouds, so called as they are induced by human activity.
You can tell this is the case by how low the base of the cloud is and that this formation was only spotted locally above Grangemouth.
The likely cause is the heat from the cooling towers of the petrochemical works here. This heat rises creating instability in the air, forcing the production of these low level cumulus clouds.
And you can thank the timing for the spectacular fiery red colours, as the particles in these clouds appear to be perfectly catching and reflecting the sunset.