A Climate Scientist’s Guide to the Oregon Coast

Transcript

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This is The Connection, a Dirty Freehub podcast connecting gravel cyclists to where they ride through short stories about culture, history, people, places, and lands.

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I’m Benjamin Purper, and today we are talking about weather watching the Oregon coast. It’s an amazing place to ride a bicycle, but how do you pick the right time of the year to ride? Can you ride in cooler seasons? Today, we’re talking with Dr. Paul Leuketh, an Associate Professor of Weather and Climate Science in the Department of Geography at Portland State University. Dr. Paul Leuketh, thanks for coming on. Thanks for having me. So first off, tell us a bit about yourself and your research.

Dr. Paul Loikith – Portland State University

Yeah, so I consider myself a weather and climate scientist. My background is in meteorology and climate science, so I’m interested in the atmosphere and how it works, both at the shorter weather time scales and the longer climate time scales. A lot of the research that I’ve been involved with involves the intersection of those two timescales. So looking at what the drivers of, in particular, extreme and impactful weather events are from the atmospheric side of things, and then understanding how they are manifested across long time periods, so climate time periods. And then another interest is how those drivers can help us understand how the frequency or intensity or the character of these extreme and impactful events may change under global warming and climate change.

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And so one of the things you study is this big type of storm called atmospheric rivers, right? And so is that something you’re really watching as a big hazard for the future?

Dr. Paul Loikith – Portland State University

Well, certainly it’s a hazard for the present and it’s been a hazard in the past and it will be a hazard in the future as well. So atmospheric rivers are really important parts of storms that affect us in the winter, the fall and the winter, particularly here in the West. But they’re important all across the world in the mid latitudes, at least both the northern and southern hemisphere. So when it comes to understanding heavy precipitation in the West, other things associated with storms like strong winds or perhaps heavy snowfall in the mountains, atmospheric rivers are really important. target of study. They’re important target of forecasting too in the short term if you just operationally want to know what’s going to happen within the weather forecast time period too. Weak and short-lived atmospheric rivers are generally considered primarily beneficial and those we don’t worry about so much except they might ruin your outdoor activity because they cause it to rain or snow. But when we get to the more uncommon but very intense, very long-lived atmospheric rivers, they’re capable of producing tremendous amounts of precipitation, especially in the west over mountainous terrain. So the coastal mountains of California, Oregon, Washington, the Cascades, the Sierra, and almost all extreme precipitation events in the west are associated with an atmospheric river. On the flip side, though, it’s important to remember not all atmospheric rivers are associated with extreme precipitation events. So they’re extremely important for our water supply, for building snowpack, ending droughts, preventing drought. But then when there’s too intense and they produce too much precipitation, that’s when we get problems with flooding and debris flows and landslides.

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OK, so these storms can be really beneficial for the environment, but they can also ruin a visit to the coast then if you happen to get caught in one, right? They can. So how far in advance should people be watching if they’re going to plan a visit or a ride on the Oregon coast somewhere? When should they start looking out for a storm that could be on its way?

Dr. Paul Loikith – Portland State University

A broad rule of thumb for weather forecast interpretation is that the further you go into the future, the more uncertain the forecast is. So you can always have more confidence if an atmospheric river is in the forecast for the 2 to 3 to 5 day time period than if it’s in the 7, 8 or 9 day time period. But these are really large systems. They’re well captured by the computer models that forecasters use. And so we can get a generally pretty good idea that at least somewhere in the region may experience a storm like this at the seven-day time frame. And as we get closer to the event, then the details start to emerge in exactly where the most intense precipitation is going to be or the biggest impacts are going to be comes into focus as we get closer and closer. But I’d say not too many of these storms sneak up on us within a seven day time frame. It can happen. It happens less and less as forecasting gets better. Beyond seven days, there’s still some information we can gain. Beyond 10 days, things get much more uncertain.

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So what role does geography play in this? Is there a big difference between the north part of the Oregon coast versus the south?

Dr. Paul Loikith – Portland State University

Probably not a very significant difference, but there is a difference. So that’s a gradient. You can think of it as a gradient from north to south. So if you average out all the numbers, you would see a difference between northern Oregon and southern Oregon, but it would be pretty small. The big difference is when we’re looking at, like, Washington and Oregon versus central and southern California. So it really depends on where the storms are. land, what path they take. Sometimes it’s perfectly dry and pleasant in the Northwest and Southern California is getting pounded by heavy rainfall. So it really depends on where that storm track sets up.

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What about wind? What should cyclists in particular know about wind on the Oregon coast and how to predict if it’s going to maybe disrupt their ride?

Dr. Paul Loikith – Portland State University

Yeah, so like with rainfall or snowfall, we have really good weather forecasts for wind. So we should be able to get a pretty good idea within a reasonable time frame of if a wind event is going to occur. They do sometimes coincide with atmospheric rivers. Atmospheric rivers are typically associated with storm systems that produce wind. But you can get wind without an atmospheric river as well. Here in Oregon, some of the worst winter wind we get, at least in northwestern Oregon, is dry and cold, not coming from the ocean. But if you’re on the coast, then it’s the other way around. It tends to be with storms coming from the ocean. So these hazards would be well-represented in weather forecasts.

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Where should people go for reliable forecasts? Some people might just open up the weather app on their phone, right, and say, oh, it’s going to be this. It’s 20% chance. I should be fine. Is there a more thorough source they should be looking at?

Dr. Paul Loikith – Portland State University

National Weather Service is a great resource and it provides a lot of information for free. There’s even forecast discussions that you can read. The experts will explain why they’re forecasting what and what they’re looking for and what the uncertainties are, what the range of possibilities are. So that’s a really great resource. There are other commercial sites that provide really detailed and accurate weather forecasts. The phone app to use a little bit of caution because it’s not always clear where the apps are getting their information. Some phone apps seem to just get direct output from some computer model that hasn’t had any human or expert intervention. And so you’re just getting a symbol that’s based on some literal thing from a computer. You probably want to make sure the forecast you’re getting has had some human eyes on it to make sure that they’re taking into account all the different forecasts and different computer models rather than some sort of algorithm that just grabs something and puts it on your phone.

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Say someone in maybe Portland or Bend is planning a trip to the coast to cycle or just to visit, and they’re planning further out than seven days. What would you say is the safest bet for month of the year, season of the year, to not get caught in a storm out there on the coast?

Dr. Paul Loikith – Portland State University

Well, summer is definitely better than winter. Even in June when we can get rain in the coast range, it tends to not be terribly stormy. So if you don’t mind the risk of getting a little wet without really hazardous storms. I would say May through September is a pretty safe bet. The likelihood of really bad weather increases as you go later into September, and it decreases as you go later into the spring. So the middle of summer is probably the safest bet. It rarely rains. It’s also rarely hot near the coast, so weather’s pretty good. And then on either side of that, you’re probably more likely than not to have reasonable weather. As you go into November, December, January, that’s when things are much less likely to be benign. But we do get nice weather in those months too. So you just have to keep an eye on the forecast.

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So your research focuses a lot on climate change and how the sort of frequency and intensity of all these storms is changing or is going to change. Can you give us a kind of broad overview of what you’re seeing and what people need to know about what the future is going to look like on the Oregon coast?

Dr. Paul Loikith – Portland State University

So at this point, it’s unclear if we’re seeing any real trend in frequency or intensity of extreme rainfall along the coast that emerges from the noise or the background variability in weather. In particular, in the Northwest, there’s really no evidence of any major change at this point. What we are seeing is things getting warmer, although in the wintertime, when the storms are active, the warming trend is much less than we’ve seen in the summertime. Summer, increasing summer heat is really a big thing that we’ve seen across the entire West. That’s really clear. But thinking about atmospheric rivers and storms, it’s not quite so clear. There’s some evidence that with more warming further into the future, really high-end rainfall events will become more intense. The rest of the events that aren’t as high-end might not shift too much. They would look a lot like they do now, just be a little bit warmer. And another thing that we will likely see is atmospheric rivers carrying more moisture. The ability of the air, the amount of moisture that the air can hold is proportional to its temperature. So as it gets warmer, it can hold more moisture. All things equal, then it could rain more, but things aren’t always equal. So it gets a bit complicated there. So we’re pretty confident atmospheric rivers will have more moisture in a warmer climate. They’ll be larger in a warmer climate. And we might see more intense extremes at the high end, but we haven’t seen that emerge in the observations at this point. Atmospheric rivers and winter rainfall in the West is extremely variable from year to year to year. And we go through periods of drought. We go through periods of floods. We have back and forth all the time, which makes it difficult to look at the record and say, oh, there’s clearly something happening, because you just see lots of ups and downs all the time. And having that long range view of things is really important when trying to put into context, say, two winters ago in California, how does that compare to previous? previous years or in the past because there have been other really intense years. So that’s all to say, current state, we don’t see a lot of obvious changes happening, but the future there likely will be some change as warming continues.

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All right, Dr. Paul Luketh, thanks for joining me. I appreciate it. Thanks for having me.

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