The 20-40 minutes before sunrise can produce the most vivid skies of the day. When high-altitude cirrus and altocumulus clouds sit above a clear horizon, the sun - still below the horizon - lights them from below, painting intense reds, oranges, and magentas across the sky.
Inverza detects this by analyzing the interplay of high cloud cover (the canvas), low cloud cover (which must be minimal so sunlight can reach the high clouds), humidity, and weather codes. When directional cloud data is available, it also checks whether the horizon toward the sunrise is clear - a wall of low cloud in that direction kills the color even if the sky overhead looks perfect.
Tip: Be in position well before the predicted time - the best color is fleeting and often peaks earlier than expected. Face east with a wide-angle lens, or isolate cloud patterns with a telephoto.
