MARY LOUISE KELLY, HOST:
Let's catch up now on a pair of storms slamming the Pacific Northwest this week, causing floods and power outages. One is a phenomenon called a bomb cyclone, the other an atmospheric river. Both are bringing high winds and a lot of rain, from Oregon to California. We're going to zoom into the northern part of California because that is where we have reached Courtney Carpenter, a meteorologist with the National Weather Service in Sacramento. Hi, there.
COURTNEY CARPENTER: Hello.
KELLY: Hi. OK, so an atmospheric river - I'm saying those words, and they sound quite lovely. I gather that these are common and that this particular one is not particularly lovely if you're in its path.
CARPENTER: Yeah. So that's actually a scientific term that we've been using for decades, but it caught wind in the public, and it's a buzzword. So it's basically a big river of moisture up in the atmosphere. And when that combines with a storm system, it brings a lot of rain to the West Coast. So that's typically how we get most of our rainfall for an entire year. Out of several of these storms, this one is just much stronger than we would typically see for this time of year.
KELLY: And I was reading a description somewhere that described it and said, think about the way that water shoots out of a garden hose. It's, like, very strong but kind of narrow. Is that accurate?
CARPENTER: Yes. These are usually narrow plumes of moisture and so they can, you know, hit just one area very hard. This one has stalled out over us, so we are talking several days of very moderate to heavy rainfall over northern portions of California.
KELLY: OK. So we've got that going on, and then I also mentioned the bomb cyclone. What is that?
CARPENTER: It's basically a storm system that strengthens very rapidly. So you can kind of compare it to when we talk about a hurricane strengthens very rapidly. It's a storm system over the Pacific, and it - the pressure in it just drops very low, very quickly, so it becomes very strong, very quickly.
KELLY: Where you are in Northern California, what kind of damage have you seen?
CARPENTER: Mostly from the winds. It's been tree damage along the coasts. Not a lot of wind impacts inland as you get into the Sacramento Valley. As far as rain goes, again, the highest impacts along the coastal areas. We've seen river flooding. We've seen small streams and creeks overflowing. We've had water rescues. Just a lot of water very fast.
KELLY: Water, water, water - is it expected to slow down over the weekend, get worse? What's the forecast?
CARPENTER: Yeah. The worst of the storm is expected to happen through today. We'll see additional light rain and heavy mountain snow into early next week, actually, but kind of the brunt of the storm system is through today.
KELLY: Anything people should keep top of mind as they're preparing for the worst of the storm?
CARPENTER: Yeah. We always ask people to pay attention when they're out traveling. There's going to be a lot of water in places we haven't seen since last winter. You never know if the road is there under all that water, so please, never drive through flooded roads. Do not go around barricades. We see a lot of fatalities from people going around barricades and driving through water. So just pay attention, especially at night when you can't see it, and think twice before you decide to drive through that standing water.
KELLY: I also was reading storms like these are actually vital for the water supply for California. Snow will be gathering in the Sierra Nevada, and you need that moisture. Is there a level on which these storms are actually good for the state?
CARPENTER: Yeah, right. It's that delicate balance. We need these storm systems for our water supply to build our snowpack, so we have water melting down the Sierra in the spring and summer and filling our reservoirs. But what happens is sometimes these storms are a little too strong, and it's too much water too fast, so it can bring some dangerous flooding risks with them.
KELLY: Sounds like it's going to be a busy weekend for you. Thanks for taking a few minutes out of your day to get us up to speed.
CARPENTER: Yeah, thanks for having me.
KELLY: Courtney Carpenter, meteorologist with the National Weather Service in Sacramento, California. Transcript provided by NPR, Copyright NPR.
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