UTC - Universal Coordinated Time
Weather observations and forecasts are usually reported in
UTC, which used to be known as Greenwich Mean Time (GMT),
i.e. the local time at the Greenwich meridian (zero degrees
longitude). This allows weather observations the world over
to have the same time stamp.
Since UTC is ahead of local time in the United States,
sometimes weather data will have tomorrow's date, but it
still represents today's data (we are not THAT good at
forecasting the weather).
UTC is 8 hours ahead of Pacific Standard Time (e.g. 0000 UTC
is 4 p.m. PST the previous day, 1200 UTC is 4 a.m. PST the
same day), 7 hours ahead of Pacific Daylight Time (e.g. 0000
UTC is 5 p.m. PDT the previous day, 1200 UTC is 5 a.m. PDT
the same day).
UTC is "Coordinated Universal Time", or "Universal Time,
Coordinated". It is UTC instead of UCT because the
abbreviation is based on the initials in French, not
English.
http://www.aldridge.com/utc.html