The 12-month period used to measure precipitation totals in the southwestern U.S. runs from Oct. 1 to Sept. 30 of the following year, and there's a very good reason.
00:00But first, it may sound a little unorthodox, but we actually just hit reset on the odometer for our California rain gauges on October 1st.
00:11This is the beginning of the new water year, so what's the deal with the water year?
00:15And why don't we just tabulate rainfall in the southwest from January 1st to the end of December?
00:20Well, the water year is a 12-month period of time that makes the most sense for measuring precipitation totals.
00:25In the southwestern U.S., most of our rainfall and mountain snow comes in between October and the month of April, tapering off into May.
00:34Then we get really dry for a long time.
00:37So this is almost like the way we measure snowfall by winter instead of by calendar year because it wouldn't make sense to hit reset right in the middle of the active time.
00:46Take a look at Los Angeles here.
00:48We see the overwhelming majority of our rainfall between October and March, tapering off into April, and then it just shuts down.
00:56So this is why, for water resource managers and also for the general public, it really makes the most sense to kind of hit start on October 1st.
01:04Here's San Francisco, even way up the coast here into central California.
01:08We get the overwhelming majority of our rainfall every year, beginning in October, and especially November through March, tapering off into April, and then it drops to almost nil through the middle of the summer.
01:21This year, we're starting off pretty well.
01:23We've had really good wet seasons.
01:26Two and three years ago, we've done pretty well, and the reservoirs are actually doing pretty well with a nice surplus here.
01:32And even last year, we did okay with rainfall.
01:35So there's this little bit of a surplus in most of the piggyback when it comes to rainfall into late this week.
01:40And this weekend, we have an increase in showers and thunderstorms with a little help from the tropics.
01:45And as we get deeper into the wet season, we're going to see more of these atmospheric river events.
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