Interpretation the weather images (radar, satellite, weather maps, etc) counts on the correct analysis of the time and also date ~ above a map. To develop a weather map, various weather facets are measured at the same time so that the chart reflects the conditions at a offered time. This is the basis of what is referred to as "synoptic meteorology" - take it all dimensions at the very same time so that the result map is a "snapshot" the the state that the atmosphere. Dimensions need come be combination to achieve this product and a typical time measurement system needs to be used. For meteorological purposes, Z-time (also abbreviation by UTC or GMT) is used. Z time is in referral to 0° longitude i m sorry runs v the imperial Observatory in Greenwich, England.

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As listed above, Z time is also referred to as Greenwich typical Time (GMT), Greenwich civil Time (GCT) or Coordinated global Time (UTC). Keep in mind that the UTC initials carry out not fit the words castle are claimed to abbreviate. This is because the unified Nations think about French to it is in the international language so the initials complement the method Coordinated global Time would certainly be composed in French.


The idea of internationaltime area was officially embraced in 1884 in ~ the InternationalMeridian Conference organized in Washington DC and also it collection the location for the prime Meridian (PM). The element Meridian, as we understand it today, is the location of 0° longitude and it is the typical for time keeping. The ar selected to be the imperial Observatoryin Greenwich, England due to the fact that this location had instituted the ideal early astronomical time determinations. In the image below, the prime Meridian is the black vertical heat on the globe to the appropriate running indigenous the phibìc Pole, through Greenwich, England, and also continuing to the southern Pole. There are 180° of longitude running to the west (red lines) and east (blue lines) of the PM. At 180° longitude, we uncover the International date Line (IDL).


The planet rotates in a counterclockwise (west to east) direction ata price of 360° of longitude in 24 hours; in one hour, the Earthrotates with 15° that longitude. Ideally, then, there shouldbe 24 significant civil time zones of equal width each of which representingone hour that time. The element Meridian serves as the main meridianfor the initial time zone. Every 15th level of longitude native thePrime Meridian is a main meridian because that a time region (15°, 30°,45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°,165° and also 180° east and also west native the prime Meridian). Eachtime zone theoretically extends 7.5° come the east and west that its centralmeridian, with some variation because that political reasons. Time area tothe eastern of the prime Meridian experience later on time 보다 that in ~ the PrimeMeridian, conversely, time zones to the west the the element Meridian experiencesearlier time than at the element Meridian...this includes the united States.

If friend were situated in the U.S. Eastern typical Time (EST) Zone, friend wouldbe close to 75°W longitude (5 times 15). At any kind of 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 climate by 5 hours.For example, noon in Greenwich (1200) is just 7 am EST. Come reduceconfusion, every times need to be express in the 24 hour time format, suchthat, 8:45 A.M. = 0845 and 1:15 P.M. = 1315. Because that a map the the worldtime zones on the U.S. Marine Observatory net site, click onto:


For a bigger map: Time ar Map


Since the collection and exchange that weather information is the internationalconcern, usage of a single global time device is required so every weatherobservers about the civilization can take dimensions at the very same time. Again, we use GMT, UTC, or often,a single letter, Z, phonetically dubbed "Zulu" to recognize the Greenwich time zone (centered on theGreenwich element Meridian). The time provided on all weather maps isgiven together Z-time, the time it is at the element Meridian.

By worldwide agreement, surface ar weather monitoring times space minimally0000 Z, 0600 Z, 1200 Z and also 1800 Z, with upper air dimensions at 0000Z and also 1200 Z every day. In the U.S., surface observations are taken hourly(at the optimal of the hour). Radar an introduction charts are also hourly at 35 minutespast the hour. Fronts space analyzed on maps every 3 hours, 0000 Z, 0300Z, and also so forth.

You deserve to use the table below to convert Z or GMT to your regional U.S. Time.The numbers in the table stand for the number of hours we are earlierthan the moment at the element Meridian.

Time ZoneStandard Time (hrs)Daylight to save Time (hrs)


Whilemost the the United says observes Daylight saving Time during the summer(early march through at an early stage November), UTC stays fixed and does not adhere come a "summerschedule". Therefore, you will have to readjust the time through one hour duringsummer. As an example, during the summer, the citizens in the U.S. EasternTime zone will lag Greenwich by only 4 hours, through 0800 EDT = 0700 EST= 1200 Z. Right here in Arizona, we carry out not usage Daylight saving Time, so us are constantly 7 hours earlier than GMT. Below is an example image mirroring a satellite cloud photo with a jet currently wind overlay. In the upper right edge of this map it states 00Z 23 AUG 2009. This time/date rubber stamp is midnight in Greenwich for this reason to figure out what time this remained in Phoenix, we have to subtract 7 hours and adjust the day if necessary. Individually 7 hours takes united state to the so late afternoon hour of 5 p.m. On 22 AUG 2009. Many start students room tricked into thinking the 00Z Sunday is ~ above Sunday. This is no the situation in the joined States. As soon as it turned come Sunday in Greenwich, England (time on this map), it to be still Saturday afternoon in the U.S., and specifically 5 p.m. Right here in Phoenix.


Two essential Z time you will certainly run into are 0Z (5 p.m. Phoenix) and also 12Z (5 a.m. Phoenix). Usual Z times are likewise 18Z (near noon in the U.S.) and 6Z (near midnight in the U.S.) it is always important come look at the moment stamp on one image very first before interpretation. If you room making a forecast, this will avoid you native interpreting old data.

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Suppose the you would like to know the present time as maintained bythe master Clock at the U.S. Navy Observatory in Washington, DC. So getyour clocks or the town hall ready and then accessibility the current time from theTime business Department at

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The following image reflects a Z-time converter the was developed by the national Weather Service. Source:


Example Z-time questions and answers

1. Convert the adhering to times from central Daylight Time in the U.S. To Z time.