天候 and 気象: a possible schedule change and weather records
Read 天候 in a canceled hike and a departure time that may change, then 気象 in records and an exhibit. Preserve the overlapping weather meanings while distinguishing possibility from completed actions.
Weather affecting a schedule
天候（てんこう） refers to weather. 「天候が悪化したため登山を中止しました。」（We canceled the hike because the weather worsened.） 悪化したため gives the reason for the cancellation. 中止しました reports the completed action of canceling the hike.
「船の出発時刻は天候によって変わることがあります。」（The ship's departure time may change depending on the weather.） 変わることがあります says that departure times sometimes change with the weather. It does not report that a particular departure time has already been changed.
Recording or presenting weather changes
気象（きしょう） also refers to weather or atmospheric conditions. 「気象の変化を一週間記録した。」（We recorded changes in the weather for a week.） 一週間 gives the period of recording. 記録した reports recording, without adding a successful prediction or an experiment.
「博物館で地域の気象を紹介する展示を見た。」（At the museum, we viewed an exhibit about the region's weather.） What was viewed at the museum was an exhibit about regional weather. Viewing the exhibit is the completed action; conducting weather observations is not stated.
Overlapping names, different sentence focuses
Both 天候 and 気象 can refer to weather. The schedule examples focus on worsening conditions or a condition affecting departure; the other examples focus on changes recorded or presented. The names do not create an exclusive short-term versus long-term division.
Compare 船の出発時刻 with 気象の変化 before reading the predicates. One is a departure time that may change; the other is weather change recorded for a week. Possibility and a completed recording are different pieces of information.
Do 「船の出発時刻は天候によって変わることがあります。」 and 「気象の変化を一週間記録した。」 both report a completed change to a schedule?
Show the answer and why
No. The first says departure time may change with the weather. The second reports recording changes in the weather for a week. What was recorded was weather change, not a departure time.