Historical clue formulations

• Obscures — 2025-03-23
• Gets hard to see through, in a way, with "up" — 2024-02-01
• Becomes difficult to see through, with "up" — 2023-06-09
• Mistifies? — 2021-03-19
• Clouds (up) — 2020-10-25
• Becomes obscure, in a way, with "up" — 2018-02-22
• Gets steamy, with "up" — 2016-07-29
• They're hard to see through — 2015-08-02
• Steams (up) — 2013-09-03
• Muddles — 2013-06-28
• Clouds (up) — 2010-01-11
• They're hard to see through — 2008-02-08
• Clouds (up) — 2006-12-27
• Obscures — 2005-05-29
• Frequent San Francisco conditions — 2003-07-09
• Reasons for lighthouses — 2002-05-13
• Heavy mists — 2002-03-04
• Airport dangers — 2000-01-24
• Beclouds, with "up" — 1997-09-26