A storm chase begins the night before. Some chasers will drive all night to get within range of storms the following day. Chasers usually make their own forecasts not only for the challenge, but also because each has a different empirical method for picking a target. But a closer inspection of the rules of storm chasing demystifies the convergence. Nearly all chasers learn to respect the dry-line, a boundary strung from western Texas to the Nebraska panhandle where hot desert air and moist air from the Gulf of Mexico meet.
Chasers meet here, too, awaiting the big storm.
With other storms developing nearby along the dryline, chasers must keep focused on the original target unless the weather pattern has changed significantly. Otherwise, they'll find themselves racing from storm to storm and will miss the best action. From a distance, a seasoned chaser can distinguish between a severe storm and a garden-variety storm. A large overshooting dome above the anvil level usually indicates a strong updraft. Midlevel cloud bands reveal the storm's rotation.