Just Google “atmospheric river” and – BAM! – the doom and gloom is in your face:

“Atmospheric river will blast California with heavy rain and snow ‘measured in feet”!

“Risk of significant California flooding”!

“California will be pummeled”!

So what is this big bad “river” in the sky that the meteorologists and their media waterboys keep screaming will be upon us starting this weekend? And must they really make it look as if the sky were, well, falling?

News reports are warning us to brace for both flood-worthy rainfall and a ton of snow in the Sierras. In fact, the wet times have already begun as Winter Storm Helena dumped the first round of heavy mountain snow and rainfall on much of the Western United States.

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Now comes ”the river.” Starting on Saturday and continuing through Monday, the forecasters are telling us, an atmospheric river will deliver even heavier rainfall and rising snow levels, possibly triggering floods that the National Weather Service says could be the greatest we’ve seen in these parts since December 2005.

For most of us, “atmospheric river” seems to be a weather term that came out of nowhere this year and is suddenly on everyone’s lips (and in their hashtags). Look, for instance, at what Daniel Swain of the California Weather Blog just tweeted:

Pretty amazing animation of water vapor transport associated with major #AtmosphericRiver event this week. #CAwx https://t.co/Pw6YTFMB8K pic.twitter.com/ZIMtQNfJai — Daniel Swain (@Weather_West) January 4, 2017

We could not have asked for a clearer picture of what an atmospheric river LOOKS like. But what in the heck is it?

We called meteorologist Brian Mejia with the National Weather Service in Monterey to help us sort it all out:

Q So is the term ‘’atmospheric river’’ a new one for you guys like it is for us laymen?

A It’s not new, I can tell you that. I’m not sure how long we’ve been using it; a couple of decades probably. But it’s something we learn in school and it’s a common phrase in meteorology.

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Q So what’s it mean?

A Typically, you hear the term more on the West Coast because we get these low-pressure systems that transport moisture and water vapor. And if they get deep enough they put out a plume, like plumes of clouds, and we’re now looking at just such a moisture plume being carried out by the storm system and into the heart of California.

Q So it really is a river in the air?

A Yes. The one we’re expecting this weekend is coming from a system that’s kind of just sitting there well off in the central Pacific and it just throws out this plume of moisture, typically from west to east or southwest to northeast. We use the river metaphor because the plume flows like a river and you can see its outline if you loop it in satellite images, being transported by the wind. That’s what’s coming to California this weekend, and it’s bigger than the river that came through earlier this week.

Q So this river will dump a lot of itself on the state?

A We won’t know until it arrives, but we’re looking at trending toward a very, very wet weekend. And it’ll affect the entire state in some way. Southern California won’t get as much rain as the central and northern parts, but there’s definitely the possibility of flooding.

Q Is the Pineapple Express, and I don’t mean the movie, such a river?

A It’s very similar. The Express is a type of atmospheric river, named that because you can see the plume coming from Hawaii into California.

Q How wide can these rivers get?

A They come in different shapes and sizes; some are more narrow bands of moisture, some are pretty thick. This one looks like it’s going to be pretty deep and very wide, which is why most of California will be impacted. We’re talking hundreds of miles wide, so at least half the state will fall within this area of transported moisture.

Q Do you yourself hear more and more people using the term ‘’atmospheric river’’?

A I do. And we’re actually trying to use it a lot in our social-media posts and our interviews because the media loves to use terms that people can understand. And the river is a good term because people can almost see that river in the sky and relate to it.

And what might this river look like once it dumps everything it’s got down upon all us?

Well, have a look:

Credit: NOAA