WHY IT GLOWSDark ground. Sunlit rocket.
Near dawn or dusk, sunlight can catch exhaust high above the dark ground, making a huge glowing plume. We flag a possible viewing window when the Sun is 2° to 12° below Oldsmar's horizon and forecast cloud cover is at most 35%.
This is a screening rule, not a visibility prediction or a percentage chance. The flight path, cloud layers, and sunlight at the actual plume can still hide the show. Alerts need a precise launch time and a Go status.