Historical clue formulations

• Humidifier's output — 2025-09-23
• Trail left by a jet — 2025-07-30
• Fog or mist — 2024-09-16
• Steamy stuff — 2024-02-22
• E-cigarette output — 2020-03-04
• Fog, e.g. — 2018-04-28
• Contrail contents — 2017-09-29
• Moisture in the air — 2017-04-03
• E-cigarette output — 2016-08-28
• Boiling evidence — 2015-03-07
• Clouds, e.g. — 2012-09-06
• Kind of trail — 2012-03-11
• Something in the air — 2006-11-08
• Water in the air — 2005-07-25
• Exhaust, perhaps — 2005-05-29
• Contrail content — 2005-05-12
• Steam, e.g. — 2003-03-19
• Gaseous mist — 1996-12-10
• Fog — 1996-08-27