Thursday, October 21, 2010

That Wild, Wacky "Zulu Time"

I've posted a lot of images and referred to specific dates and times in those images this week, more so than I normally do (using computer model guidance anyway), and that has raised a question about "time" from several readers...

Most of their questions/comments go something along the lines of:

"Are you keep saying the model image is valid at 7pm CDT on Wednesday, 10-27-10, when it clearly says on the time stamp on the model image that it is valid Thursday 10-28-10".

To further illustrate their point and my response, please see the sample image below, from my latest post on the upcoming major weather pattern change to take place across the country next week:

While it's true that the day/date stamp on the image says "THU 101028", which decodes to Thursday, the 28th of October, 2010, if you look a little further to the right of the "slash" (/), it says "0000V168".  The "0000" refers to 00:00 Greenwich Mean Time (GMT), also known as 00:00Z (Z being "Zulu" time).

For whatever reason, the global meteorological community chose to use GMT or Z time many years ago when establishing protocols.  For more on Greenwich Mean/Zulu time, see a link here.

Anyway, as you've probably already figured out, 00:00 pretty much universally stands for Midnight, so Midnight on 10-28-10 would actually equate, in the central U.S. time zone, to 7:00 PM (on the 27th).

So, there you go.  I'm not's just that wacky zulu time messing with your head (and mine)!

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