How do you define daytime and evening times in a weather forecast?

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Dear Tom,
Could you define the forecast periods in a weather forecast?
— Kip Pope, Champaign
Dear Kip,
Your question is important because a weather forecast loses its effectiveness if the public does not understand it. Here are the basic time period breakdowns based on standard time. During daylight saving time, one hour is added.
Today: 6 a.m.-6 p.m.
Tonight: 6 p.m.-6 a.m.
Morning: 6 a.m.-noon
Early morning: 6-9 a.m.
Mid-morning: 8-10 a.m.
Late morning: 9 a.m.-noon
Afternoon: noon-6 p.m.
Early afternoon: noon-3 p.m.
Mid-afternoon: 2-4 p.m.
Late- afternoon: 3-6 p.m.
Evening: 6-9 p.m.
Late evening: 9-midnight
Late at night: Midnight-6 a.m.
Toward morning: 3-6 a.m.

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