California's rain season is short-term pain for long-term gain

AccuWeather

Bernie Rayno analyzes the drought areas in California and the small window California has for rain in the winter months.

Transcript

00:00You always hear me say when it comes to California, and especially rainfall, short-term pain,

00:08because of always the risk for flooding, for long-term gain, keeping the drought at bay.

00:15That's what that term means. And in California especially, and really across much of the West,

00:21where we continue to have a large population living in areas where you don't get enough rain,

00:27water is as precious as gold. That's why we focus so much on the drought monitor that show us where

00:35things are dry. And in California, it's a little tricky. Let me show you the latest drought monitor.

00:40So if you would take this verbatim, you would say, well, Southern California is in a drought here.

00:45You do have some moderate to severe drought in Southern California, no problems really in

00:51Central California. And quite frankly, where you see the areas that are dry, that is not drought.

00:56However, it's not the only metric we look at when looking at California. I think the most

01:02important thing here is how are the reservoirs doing? The two biggest reservoirs in California are these,

01:14Shasta and Oroville right now. And you can see that these reservoirs are fine. In fact,

01:25compared to historical average, they're running above normal in Shasta, near normal in Oroville.

01:30But all the other ones as well, from Folsom down toward Castiac, we actually have plenty of water

01:35given the historical averages. Now, that does not mean you need to stop conserving. That's not what I'm

01:43getting at. But right now, there is not a water shortage in California. There just isn't. I don't

01:50really care what it says on the drought monitor. We have plenty of water for now. Unfortunately,

01:56California is susceptible to droughts. And here's why. You have a short window, a very short window

02:03to pick up your rain in California. Here's the average rainfall per month in California. And you'll

02:10notice this. Basically, from May through September, let's even be generous, in October,

02:16you don't get any rainfall. 99% of your rainfall in California happens in the winter months will

02:23start as early as October. But October, November, but especially December, January, February, and in

02:30the March. But if you include October here, those months you average about 13 inches of rain, a little

02:37over a foot of rain. And then you will not get a drop of rain for the rest of the year. That's why

02:43we concentrate so heavily on what happens during the wintertime. Now, in Southern California,

02:50you go through long stretches where you don't get any rain. But when it does rain, it generally pours

02:57and you have to worry about flash flooding. And that's exactly my concern moving forward here with

03:03our system. Let me show you the setup here as we look at the satellite here this morning. I'll put this

03:08into motion. And again, you've got the upper level low off the California coast right here. Now,

03:14you see all these clouds? You're already getting some rain and wind across Central and Northern

03:19California. Now, if this upper low would be moving this way, I would be worried about flooding in San

03:25Francisco, in Sacramento, and much of Northern California, but it's not going to. In fact, what

03:31it's going to do is it's going to be moved south. It's going to be pushed south by all of this.

03:36You see these clouds up in here in the Gulf of Alaska? That's going to take this upper low

03:41and ram it southward where it's going to meet up with this. Look at this tropical moisture coming

03:46northward. Here's a Hawaii, but off to the south and east, you've got this feed of moisture coming

03:51into Southern California with this upper low. And that's one of the reasons why I think it's going

03:56to pour. Let me show you what the pattern is going to look like here. We're going to look at the

04:00American model and the European model, and they're both aligned on what this upper low does.

04:06Take a look at it. Here we are for this evening. I'm going to play this through. This is the

04:10European model. Watch what it does. Let's go through Friday morning, Friday evening, and then

04:16Sunday, Saturday morning, Saturday afternoon. Look at this upper low, the way it's, I'm going to stop

04:21it right here. 7 a.m. Saturday morning, European, American, European, American, European model,

04:28American model. They're both the same. How about Sunday afternoon, European, American model,

04:33both the same. This is an ideal setup for heavy rain in Southern California, and here's why.

04:38You've got the upper low off the Southern California coast, but notice these black lines

04:43here. They're coming in from the west-southwest. You could even see the wind barbs coming in out

04:48of the west-southwest. So all of that tropical moisture with the upper low is getting rammed northward

04:55in the Southern California. And armed with the knowledge of how the topography works in California,

05:01you could see why I'm so worried about the heavy rain. In fact, let me zoom in. Look at what's going

05:08on here. Here we go. This map illustrates it. Los Angeles County, Orange County, San Diego County.

05:15You see these mountain ranges in here? Look how they face. Yeah. They face off to the west-southwest

05:21here. And with that, what's happening is you're taking all of that moisture and you're ramming

05:28it northward into these mountains. Now, there's going to be heavy precipitation to begin with,

05:32but because of that mountain range, you're going to get that precipitation to enhance because of the

05:39increased upward motion from what we call orographic lift or upsloping, that air being forced to rise

05:47along the west slope of the mountains. And what happens is you get more precipitation and it gets

05:52even heavier. Now, we're already looking at rain in Northern California and Central California

05:59from what started last night, but even in the Friday here. Most of California gets at least an

06:04inch, if not two inches of rain. But even tonight into tomorrow, you're going to start seeing rainfall

06:09amounts in Southern California, about a half inch to an inch. That's going to cause some travel delays,

06:14but it's not going to cause any flooding. But once that upper low gets off the Southern California

06:20coast, when? Friday night and Saturday. Look what happens. Look what happens here. Look at the

06:26rainfall here in the LA basin, two to four inches. And in the upslope areas and the mountains to the

06:31north and west, there could be over six inches of rain here. Some spots will get a double-digit

06:35rainfall. And when you add all of the rainfall that we're going to see with this storm, you can easily

06:41see five to six inches of rain. And that's about 20 to 30% of the winter rainfall. That's a big deal

06:50on the feed.

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