Jerusalem sits at about 2,500 feet (760 m), so winter from December to February is cool and wet, with occasional snow, while the Dead Sea and Jericho below sea level stay warm. June to September is hot and dry everywhere and above 100 F (38 C) in the Jordan Valley; groups that travel then start early and rest at midday. The Christian Information Centre runs the Holy Sepulchre on a summer timetable (5:00 a.m. to 8:45 p.m.) and a winter one (4:00 a.m. to 7:00 p.m.), which shifts Mass bookings at Calvary and the Tomb by an hour.
Holy Week is the fullest week of the year in the Old City, with the Latin and Orthodox calendars sometimes coinciding; in 2027 Latin Easter is March 28 and Orthodox Easter May 2, so the crowds are split. Mass at the Tomb in Holy Week is booked many months ahead through the Franciscan Pilgrims' Office.
Jewish holidays matter even for a Catholic group because Israeli transport, shops and many museums close from the evening before. In 2027: Passover April 21 to 29, Shavuot June 10 to 12, Rosh Hashanah October 1 to 3, Yom Kippur October 10 to 11 (when the country effectively shuts down, airport included), Sukkot October 15 to 22 and Simchat Torah October 22 to 24. Each begins at sundown the previous evening. Shabbat closes public transport from Friday afternoon to Saturday night every week. The security picture also shapes timing; the State Department advisory is the first check, whatever the season.