Before launching, pilots will call a weather service to find out about climate and wind conditions in an area. Cautious pilots only fly when the weather is close to ideal -- when skies are clear and wind conditions are normal. Storms are extremely hazardous for hot air balloons, because of the danger of a lightning strike. Even rain is a problem, because it decreases visibility and damages the balloon material (of course, it's not much fun to fly around in wet weather anyway). And while you need a nice wind current to have a good flight, very strong winds could easily wreck the balloon.

Pilots also call the weather service to get a rough idea of which way the balloon will travel, and how they should maneuver once they're in the air. Additionally, a pilot might send up a piball (short for pilot balloon). A piball is just a balloon filled with helium that the pilot releases to see the exact direction of the wind at a prospective launch site. If it looks like the wind would take the balloon into prohibited air space, the crew needs to find a new launch spot.

Typically, a balloon will only fly just after sunrise in the morning, and just before sunset in the evening.  This is when the winds are mostly calm, which provides for a safe flight.  As the sun comes up, the earth's surface begins to warm, which creates wind.  Therefore it's best to fly just as the sun comes up, or as it's beginning to set, to assure the least amount of wind.