Gusty Winds, Rain Expected in San Diego County
KPBS Midday Edition Segments / May 15, 2019
Gusty winds will buffet the San Diego County mountains and deserts Wednesday ahead of a low-pressure system that will bring a chance of rain throughout the region on Thursday, according to the National Weather Service.
Speaker 1: 00:00 Forecasters say San Diego is in for another spring storm tomorrow and what's turning out to be an unusually rainy may and northern California is already getting rain. The first of three storms forecast through the beginning of next week. California's May rain is being set in motion by yet another atmospheric river. Moving in across the Pacific rain is generally a good thing for the state, but we don't really have the ability to prepare for it or use it. I Uc San Diego research project is trying to change that journey. Me as Dr Marty Ralph, research meteorologist at scripts and director of the center for Western weather and water extremes and Dr Ralph, welcome to the program.
Speaker 2: 00:40 Thank you.
Speaker 1: 00:41 Now could you start by reminding our listeners what and atmospheric river is and why it happens?
Speaker 2: 00:48 Yeah, that must be river is essentially a river in the sky, but it's water vapor being blown along by the wind rather than liquid. You don't want a river on land. They tend to be a a couple hundred miles wide and a couple thousand miles long and they can transport massive amounts of water vapor horizontally. Something like 25 Mississippi. If Water in this vapor
Speaker 1: 01:10 now we've felt some atmospheric rivers already this winter. Can you remind us what they were and what they did to California?
Speaker 2: 01:18 Oh yeah. We had a very active winter of a atmospheric river, a storm sit in California. Uh, some were actually a very, very strong and we've developed a scale for them now and those from one to five and we had a couple of 10 glory for storms this winter, which are the ones that can really produce hazards, some plots in the light.
Speaker 1: 01:41 So what can we expect this time?
Speaker 2: 01:43 This one is unclear yet the forecast is still, I was variable, but it could be as much as a category to a r n central and northern California. Yesterday's forecasts had it coming into even San Diego's category too. But today's forecast has got it. Stay in Fargo north.
Speaker 1: 02:02 You noticed that meteorologists in California haven't had an adequate way to describe the intensity of these atmospheric rivers storms. Tell us about that.
Speaker 2: 02:12 Yeah. Covered over the last 15 years or so. Uh, how important is that in the free quivers our to our water supply and to flood the first thing we really come down with the big crowd for the West Coast or from atmospheric rivers and that became the type of uh, finding that became well known in the public and you on meteorologist on TV and the like. So when we started seeing atmospheric rivers coming in the forecast that was the natural yaks and that was this good. This is going to make a big flood, but the reality is the weaker they are are not really likely to produce major flooding, but they can produce very beneficial water supply.
Speaker 1: 02:48 And so what does your new scale indicate?
Speaker 2: 02:51 We have a scale that goes from one to five and a category one and two a ours. Those are mostly beneficial. Okay. It hits right at the end of the big storm. It's already caused flooding is going to have some problems, but most of them are going to be largely providing additional water supply, which most people know we need when we're getting up to category four or five, which we refer to as the major Ar. Those are largely associated with hazards. So some of the major flooding we have in California this year was associated with [inaudible] for ars and uh, some of the big historical flooding on the west coast. No category four category five ours.
Speaker 1: 03:31 How long has California Been Affected by atmospheric rivers? I mean, is this a new phenomenon?
Speaker 2: 03:37 The phenomena has been around forever. It's a natural part of how the atmosphere works. If you go to anywhere in the mid Atlantic, the globe atmospheric rivers account for, you know, something like 90% of the horizontal water. They pretend support for the curves. So they're really where the water vapor is moving along horizontally and you're feeding into storms and they've been around forever,
Speaker 1: 03:59 so they've been around forever. But are, are there, they increasing in frequency here in California
Speaker 2: 04:06 there are changes anticipated time when it was warmer it can hold more water vapor and this was when the water vapor in the air, it can produce more per foot. The patient
Speaker 1: 04:17 is this phenomenon unusual to have in May?
Speaker 2: 04:20 They're not uncommon. They don't happen every year. If I look back over the last 10 years or so, about every other year on average will have any ar two
Speaker 1: 04:30 now, Doctor Ralph, your center studies, Western weather and water extremes. What other kinds of extremes are you studying?
Speaker 2: 04:39 Well, we're working on the summer months to him as well. Uh, you know the summer rains would come to Arizona and southern California Yukon in the light and heavy winter. Smos are also a key topic of our interests and those often come know him. Atmospheric rivers, storms, which produced about 40% of the average snow pack this year, each year. Those are the main types of storms are working on the ones who really impact our water.
Speaker 1: 05:06 A couple of meteorologists working with the San Diego gas and electric. Um, a couple of years ago came up with a scale rating Santa Ana wind events. I wonder what is the purpose of these scales? What, what do they tell us? What should they be telling us when we rate wind events or when we rate atmospheric rivers?
Speaker 2: 05:28 These skills really help in terms of raising situational awareness. Situational awareness is something, uh, individual fab. When you're looking ahead in time, like a day or a week, if you have a sense that there's a potentially potent storm coming a few days out or actions that you might be able to take to prepare for that you going, the forecast isn't perfect. So for example, in emergency management and emergency response, if they have or where there's a risk of living against storm a few days out, they may start pre positioning equipment and people, you know, to deal with the flooding that might occur and that prepositioning helps reduce response times and improve, you know, outcomes for, uh, emergency, uh, response. This situational awareness, uh, aspect is very important in many areas. And for the west coast, we really haven't had, uh, a way to distinguish the storms that are really going to be potentially potent from those that are less. So, uh, we've had detailed forecasts, have you precept in one spot or wasn't there, whatever. But it's all encapsulated now in this atmospheric river concept. Much like when it comes to hurricanes, there's flooding or storm surge, there's tornadoes, there's high winds when there's a hurricane warning. All of those details are sort of, people are alerted to the fact that those things to happen.
Speaker 1: 06:52 Yeah. Atmospheric River that's headed our way though this week. Looks like it's going to be beneficial so far.
Speaker 2: 06:57 Absolutely. It was probably a year to have the rainy season extended, uh, helps shorten the fire weather season and, uh, you know, helps keep the vegetation feel fresh.
Speaker 1: 07:08 I've been speaking with Dr Marty Ralph Research meteorologist at scripts, director of the center for Western weather and water extremes. And thank you so much. Thank you.
Speaker 3: 07:19 [inaudible].