METEOROLOGIST JEFF HABY
Z time is used in order for
all meteorological measurements to be made at the same time. This is the basis for
synoptic meteorology, to take all measurements at the same time to produce a snapshot of the state of the atmosphere.
Z time is in reference to 0 degrees longitude at Greenwich, England. The 12Z time will be in the early morning hours
in the United States. Relative to Central Time, 12Z is at 6 a.m. in January (Central Standard Time) and 7 a.m. in
July (Central Daylight Time). The way to remember the difference between CST and CDT is to remember that there is
more Daylight in the summer and therefore the warm half of the year is Daylight time and the cool half of the year
standard time. When it is noon in Europe, it is the early morning hours in the United States. 0Z occurs in the
late afternoon hours in the United States. Relative to Central Time, 0Z is at 6 p.m. (Central Standard Time) and
7 p.m. (Central Daylight Time).
Many beginning analysts are tricked into thinking 0Z Tuesday is on Tuesday local
time. This is not the case in the United States. When it turns to Tuesday in Greenwich, England, it is still Monday
afternoon in the United States. Remember that Europe will always have their New Year's celebrations before the
United States. 0Z TUE on the chart occurs at 6 p.m. Monday (Central Standard Time). The most common Z times you will
come across are 0Z (late afternoon in U.S.), 18Z (near noon in U.S.), 12Z (morning in U.S.) and 6Z (near midnight in U.S.).
It is a wise habit to look at the time stamp first on an image before interpretation. This prevents the unwanted task
of interpreting old data. Most of the major synoptic scale models will have time stamps of 12Z or 0Z since most
synoptic models are run twice per day. Surface analysis charts are updated hourly or every 3 hours. It is wise to
be able to convert your local time into Z-time and vice versa for your time zone.