Weather Blog

Don't trust that calendar -- summer begins Saturday!

Don't trust that calendar -- summer begins Saturday!

Today's weather lesson is on time zones, and how they are messing with Seattle as far as the first day of summer.

Did you fall for the "East Coast bias" and believe that Sunday is the first day of summer? Actually, it begins Saturday night at 10:45 p.m., but of course, that's 1:45 a.m. EDT, and since most of the national media resides there, Sunday is getting all the attention.

Even many calendars are in on the Sunday gig, but that's because they use what amounts to the old Greenwich (England) Mean Time standard, which used to be the official world time location until it moved to France and the official time became known as "UTC" time.

UTC stands for "Universal Time, Coordinated" and while that sounds funny in the same sense as "Weather Outlook, Puget Sound", it was actually a carefully crafted compromise between the English (who wanted "Coordinated Universal Time") and the French ("Temps Universel Coordonné").

So they took CUT and TUC and mashed it to come up with UTC so no one got what they wanted.

Those in the military might have also referred to this as "Zulu" time (don't ask) and even in the field of meteorology, you'll see our forecasting products based on "Z" time, which is the same as Zulu, which is the same as UTC and the old GMT (but definitely not CUT or TUC!)

Anyway, UTC is 7 hours ahead of PDT and that's why all the calendars say 5:45 a.m. Sunday, when it's actually 10:45 p.m. Saturday for us.

So let's go back to weather, which as I mentioned, uses "Z" time as our universal time so we're all on the same page no matter what time zone you are in.

Those of you who read the National Weather Service Forecast Discussion might see forecasting models referenced in this way, as they are issued at 0Z, 6Z, 12Z and 18Z.

The easy way to remember it is that 0Z is the evening model (issued at 5pm PDT) and 12Z is the morning model (issued at 5am PDT.)

But it gets even more confusing when it's 0Z, since that is midnight and actually tomorrow. So a forecast model for, say, 0Z on the 23rd is actually for the evening of the 22nd in Seattle. If only tax forms were that simple.

In summary -- don't fall for the hype! Summer begins Saturday! Enjoy its early arrival!