A forecast has a timeline.
A TAF is a forecast, not an observation. Follow one example through the day and separate the prevailing picture from temporary changes.
TAF KJFK 011130Z 0112/0212 22010KT P6SM SCT030 TEMPO 0114/0118 3SM SHRA BKN015 FM011800 28012KT P6SM SCT040
Day 1, 15:00 UTC
Prevailing: wind from 220° true at 10 kt; visibility over 6 statute miles; scattered cloud at 3,000 ft AGL.
Temporary changes possible: visibility 3 statute miles, rain showers and broken cloud at 1,500 ft AGL. These are possible interruptions, not continuous conditions throughout the window.
Valid from day 1 at 12:00 until day 2 at 12:00 UTC. The slider samples each hour before the validity ends. Cloud heights are above ground level (AGL).
Two groups. Two different jobs.
FM: a new prevailing picture
FM011800 starts a new set of prevailing conditions at 18:00 UTC on day 1. In this example it replaces the earlier prevailing group.
TEMPO: interruptions within a window
TEMPO 0114/0118 covers day 1 from 14:00 to 18:00 UTC. Temporary fluctuations each last less than an hour and together cover less than half the period. It does not forecast four hours of uninterrupted poor weather.
Read the dates as well as the hours
0112/0212 crosses midnight: day 1 at 12:00 to day 2 at 12:00. This example focuses on FM and TEMPO; other change and probability groups need their own interpretation.