14 CFR § 101.39 - Balloon position reports.
(1) The current geographical position.
(2) The altitude.
(3) The forecast time of penetration of 60,000 feet standard pressure altitude (if applicable).
(4) The forecast trajectory for the balance of the flight.
(5) The forecast time and location of impact with the surface of the earth.
(c) If a balloon position report is not recorded for any two-hour period of flight, the person operating an unmanned free balloon shall immediately notify the nearest FAA ATC facility. The notice shall include the last recorded position and any revision of the forecast trajectory. The nearest FAA ATC facility shall be notified immediately when tracking of the balloon is re-established.