Possible Clues:

• Frequent San Francisco conditions
• Becomes hazy, with ''up''
• Becomes obscure, in a way, with 'up'
• They often 59 Across
• Horror film effects
• Breathes on glass, say
• Becomes difficult to see through, with 'up'
• Low-visibility conditions
• ___ up (gets steamy)
• Becomes 37 Down, with ''up''