Interpretation of weather imeras (radar, satellite, weather maps, etc) relies on the correct analysis of the time and day on a map. To create a weather map, assorted weather elements are measured concurrently so that the chart shows the conditions at a provided time. This is the basis of what is dubbed "synoptic meteorology" - take all dimensions at the very same time so that the resulting map is a "snapshot" of the state of the setting. Measurements should be coordinated to accomplish this product and a conventional time measurement system needs to be supplied. For meteorological functions, Z-time (additionally abbreviated by UTC or GMT) is supplied. Z time is in referral to 0° longitude which runs via the Royal Observatory in Greenwich, England.

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As provided above, Z time is additionally described as Greenwich Mean Time (GMT), Greenwich Civil Time (GCT) or Coordinated Universal Time (UTC). Keep in mind that the UTC initials execute not fit the words they are intended to abbreviate. This is because the United Nations take into consideration French to be the international language so the initials match the method Coordinated Universal Time would certainly be created in French.


The idea of internationaltime zones was officially adopted in 1884 at the InternationalMeridian Conference organized in Washington DC and it set the location for the Prime Meridian (PM). The Prime Meridian, as we know it this particular day, is the location of 0° longitude and also it is the traditional for time maintaining. The location selected was the Royal Observatoryin Greenwich, England bereason this area had instituted the ideal early on huge time determinations. In the photo below, the Prime Meridian is the babsence vertical line on the globe to the best running from the North Pole, with Greenwich, England also, and continuing to the South Pole. Tbelow are 180° of longitude running to the west (red lines) and eastern (blue lines) of the PM. At 180° longitude, we discover the International Date Line (IDL).


The Planet rotates in a counterclockwise (west to east) direction ata rate of 360° of longitude in 24 hours; in one hour, the Earthrotates with 15° of longitude. Ideally, then, there shouldbe 24 major civil time zones of equal width each of which representingone hour of time. The Prime Meridian serves as the main meridianfor the initial time zone. Eextremely 1fifth degree of longitude from thePrime Meridian is a main meridian for a time zone (15°, 30°,45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°,165° and 180° east and also west from the Prime Meridian). Eachtime zone theoretically exhas a tendency 7.5° to the eastern and also west of its centralmeridian, through some variation for political factors. Time areas tothe east of the Prime Meridian endure later on time than that at the PrimeMeridian, whereas time zones to the west of the Prime Meridian experiencesearlier time than at the Prime Meridian...this consists of the USA.

If you were located in the U.S. Eastern Standard Time (EST) Zone, you wouldbe close to 75°W longitude (5 times 15). At any place in this zone,you would certainly be 5 hours different from time in Greenwich, England.With the Earth rotating eastward, Greenwich is ahead of EST then by 5 hrs.For instance, noon in Greenwich (1200) is just 7 AM EST. To reduceconfusion, all times need to be expressed in the 24 hour time format, suchthat, 8:45 A.M. = 0845 and also 1:15 P.M. = 1315. For a map of the worldtime zones on the UNITED STATE Naval Observatory internet nlinux.orgsite, click onto:


For a larger map: Time Zone Map


Because the repertoire and also exchange of weather indevelopment is of internationalissue, usage of a single global time device is essential so all weatherobservers approximately the world have the right to take measurements at the very same time. Again, we usage GMT, UTC, or often,a single letter, Z, phonetically dubbed "Zulu" to recognize the Greenwich time zone (focused on theGreenwich Prime Meridian). The time offered on all weather maps isprovided as Z-time, the time it is at the Prime Meridian.

By international agreement, surconfront weather monitoring times are minimally0000 Z, 0600 Z, 1200 Z and also 1800 Z, via upper air dimensions at 0000Z and also 1200 Z each day. In the U.S., surchallenge monitorings are taken hourly(at the height of the hour). Radar summary charts are likewise hourly at 35 minutespast the hour. Fronts are analyzed on maps eexceptionally three hrs, 0000 Z, 0300Z, and also so forth.

You deserve to usage the table listed below to transform Z or GMT to your regional UNITED STATE time.The numbers in the table reexisting the variety of hrs we are earlierthan the moment at the Prime Meridian.

Time ZoneStandard Time (hrs)Daylight Savings Time (hrs)


Whilea lot of of the United States observes Daylight Saving Time throughout the summer(at an early stage March via at an early stage November), UTC stays fixed and does not adbelow to a "summerschedule". Thus, you will certainly need to change the moment by one hour duringsummer. As an instance, during the summer, the occupants in the UNITED STATE EasternTime zone will lag Greenwich by just 4 hrs, through 0800 EDT = 0700 EST= 1200 Z. Here in Arizona, we execute not use Daylight Saving Time, so we are always 7 hours earlier than GMT. Here is an example image reflecting a satellite cloud photo through a jet stream wind overlay. In the top best corner of this map it states 00Z 23 AUG 2009. This time/date stamp is midnight in Greenwich so to figure out what time this was in Phoenix, we need to subtract 7 hrs and readjust the day if essential. Subtracting 7 hrs takes us to the late afternoon hour of 5 p.m. on 22 AUG 2009. Many beginning students are tricked right into thinking that 00Z Sunday is on Sunday. This is not the situation in the United States. When it turned to Sunday in Greenwich, England also (time on this map), it was still Saturday afternoon in the UNITED STATE, and also especially 5 p.m. right here in Phoenix.


Two vital Z times you will certainly run into are 0Z (5 p.m. Phoenix) and also 12Z (5 a.m. Phoenix). Typical Z times are additionally 18Z (close to noon in the U.S.) and 6Z (close to midnight in the U.S.) It is always vital to look at the moment stamp on a photo first prior to interpretation. If you are making a foreactors, this will certainly prevent you from interpreting old data.


Suppose that you would certainly favor to know the current time as kept bythe Master Clock at the U.S. Naval Observatory in Washington, DC. So getyour clocks or watches prepared and then accessibility the current time from theTime Service Department at

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The complying with photo mirrors a Z-time converter that was created by the National Weather Service. Source:


Example Z-time questions and also answers

1. Convert the complying with times from Central Daylight Time in the UNITED STATE to Z time.