Long before any app updates, the sky overhead has already announced what is coming. Nine cloud shapes, nine forecasts, and the last one is the one pilots steer around.
Cirrus are ice crystals above 20,000 feet, far too thin to rain on anyone. But they often ride ahead of a warm front, so rain tends to follow within a day.
When cirrus thickens into a milky sheet, its ice crystals bend sunlight into a ring exactly 22 degrees wide. The old rhyme is right: a halo means weather is on the way.
Altocumulus break the sky into rippled scales, the classic mackerel sky. Seen on a humid summer morning, they warn of unstable air aloft and storms by mid-afternoon.
A featureless grey lid sitting low over everything is stratus. It is fog that never reached the ground, and it drizzles rather than pours: grey all day, but not stormy.
Fair-weather cumulus all sit on one invisible shelf. That flat base marks the exact height where rising air cools enough to condense, and while they stay squat, it stays dry.
When those puffs sprout cauliflower towers taller than they are wide, the updraft is winning. Congestus clouds usually deliver a shower within the half hour.
A tower that reaches the stratosphere can climb no further, so it spreads sideways into an anvil. That flat lid is the signature of a real thunderstorm, seen here from orbit.
Mammatus hang in sagging lobes beneath a storm's anvil, formed where cold air sinks into warmer air below. They mark a powerful storm, usually one that has just passed over.
Smooth, stacked and motionless above a ridge, lenticular clouds sit in a standing wave of air. The cloud holds still while fierce wind pours through it, so pilots steer clear.
Height, shape, and how fast it is changing. Those three cues cover most of what a sky can tell you, and the top of the sky is where tomorrow shows up first.