State Climatologist Dr. Justin Glisan

Kay Henderson

Heat, heavy rain, severe weather. We've had it all recently. We'll talk about our weather, climate and the outlook with State Climatologist doctor Justin Gleason on this edition of Iowa Press.

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For decades, Iowa Press has brought you political leaders and newsmakers from across Iowa and beyond. Celebrating more than 50 years on statewide Iowa PBS, this is the Friday, July 17th edition of Iowa Press. Here is Kay Henderson.

Kay Henderson

I think we've all heard that saying, it's not the heat, it's the humidity. But maybe it's both right now. Our guest today will walk us through some of the weather that we're having and the records that may have been set. Dr. Justin Glisson has been with us before at the Iowa Press table. He holds degrees in meteorology and atmospheric sciences. He was a research atmospheric scientist at Iowa State University before he was hired in 2018 to be the state climatologist. Welcome back to Iowa Press.

Justin Glisan

Always nice to be here. Thank you.

Kay Henderson

Joining our conversation is Erin Murphy, Des Moines bureau chief for The Gazette in Cedar Rapids.

Erin Murphy

Justin, I don't have the data on this. I just have the anecdotal evidence. But Kay is right. It is both hot and humid. We're hearing a lot of people talk about the corn sweat. Is that first of all, is that a real thing? Is that a scientific term?

Justin Glisan

It is.

Erin Murphy

And is that what's going on right now?

Justin Glisan

Yes. Corn sweats are the bane of my existence this time of year. Yes, it's evapotranspiration of any crop or tree leaf. Anything that's green emits water vapor. Now, when we talk about how humid it's been, it's the moisture from the Gulf. We have billions of gallons of water vapor coming from the southern states up into the upper Midwest. You think about corn sweats or the amount of water vapor that's put off by crops, about 40,000 gallons per acre per day. When you're talking about billions of gallons of water vapor from the Gulf, it's much of a 3 or 4 orders of magnitude below. It can add two, three degrees to the dew point. But when your temperatures are in the 90s and your dew points are already up in the 70s, it's not really going to matter really.

Erin Murphy

We are all victims of looking at things in the micro and not the big picture. We're very much in the in the now. Is this stretch that we're in now pretty normal for this time of year?

Justin Glisan

You know, the longevity of this stretch. And we've had two heat domes build in that have given us these warm temperatures. You look at the year to date temperature average, we're about three degrees above average. That's pretty warm for an annual temperature. This doesn't help. Having these higher dew points, though, does help at least mitigate some moisture stress on corn and beans as we're going through pollination for corn. Given how dry conditions are in north central and northwest Iowa, these higher dew points, while oppressive for humans and livestock out there if you're working outside, there's a silver lining there for in terms of crops. Yeah.

Erin Murphy

All right. And the farm bureau is going to ask more about the crops later. But I wanted to, you mentioned the term heat dome. That's an interesting thing that's going on right now, too. Tell us more about that, what that is and how it's impacting us.

Justin Glisan

So in the meteorological parlance, it's a warm core, high pressure. And warm core, meaning it's a very warm, stable feature in the atmosphere that persists. Being so stable, it takes a lot of energy to push it off. So when that heat dome sets up, you get two things occurring. You get southern flow into it under the dome. But you also have downward motion in that high pressure, which compressionally heats the air as well. So you're having two sources of external heating that produce these very warm temperatures. But also with the gulf being wide open, you're getting moisture underneath of it. Think of a pot of boiling water, everything underneath that boiling underneath that, the top on the on the pot is stable. And then you get steam on the outside. That's where we see the ring of fire. And this is where we see thunderstorms or disturbances moving along that heat dome. And this is where we get those substantially heavy rain events that we've seen recently.

Kay Henderson

Well, I was going to ask about the Thunderdome.

[Laughter]

Justin Glisan

Two men enter, one man leave.

[Laughter]

Kay Henderson

Exactly. So there was some flash flooding in central Iowa recently. And one of the things about it that's interesting is that these are not storms that are moving at a normal pace. What is causing these storms to just sit over an area and dump an enormous amount of rain?

Justin Glisan

Excellent point. So no steering flow. Underneath that dome, you don't have steering flow to push these thunderstorms off. These thunderstorms rain out. That rain hits the surface, cools the air. You get a cool cold pull underneath of it. It forces up warm air in front of it. You get updrafts that form. So thunderstorms forming in front of other thunderstorms. We call it training. And with no forcing to push them off, they sit over the same region. They feed off all the moisture that's coming up into the heat dome. And that's where you get two, three, four inches of rainfall over several hours. You look at the past event that we had July 3rd, July 2nd into July 3rd, 8 to 12 inches in 24 to 36 hours over a little portion between here and Ames. Some, you look at the annual exceedance probability. We think of the 500-, 1,000-year flood. That's past parlance. We look at how often these events can occur. 0.01% of the time we get an event like we saw on July 2nd into July 3rd. But we've seen three of those this year.

Kay Henderson

So you talked about past parlance. We've lived through a 500 year flood several times. So is that just sort of passe? We don't use those terms anymore?

Justin Glisan

We're looking more at floodplains, 500 year floodplain, 1,000 year floodplain. I'm from Saint Louis. We talk about the 1993 drought or not drought, the opposite of drought, 1993 flood that was above a 500 year flood. That's why we're using annual exceedance probabilities. These events don't happen often, but they can happen more than once a year. And that's why we're moving away from those terms.

Erin Murphy

There's been flooding, but there's also dry conditions, especially in western Iowa right now. Drought conditions. Real quick, what's leading to that?

Justin Glisan

Northwest Iowa, North central Iowa have missed out on widespread rainfalls through this season. You really have to think back to the 2020 through 2024 drought. Stations across the state missed out on at least one year's worth of rainfall. So when you get into hot and dry conditions, you don't see regular rainfalls. We had a very dry winter, a very dry fall. Those longer term precipitation deficits reemerge. They show us where the driest parts of the state are. North central, northwestern Iowa. So you look at that drought coverage map, about 12% D-1 moderate drought, and then about 30% abnormal dryness, D-0. You look at southern Iowa. We've had a lot of rainfall southern Iowa into central Iowa. But we've been dry over the last 7 to 14 days. That's where we can start to see drought reemerge.

Erin Murphy

And that's specifically to Iowa. If you broaden it out to more regionally, eastern South Dakota and eastern Nebraska are in much heavier drought. Is that something that's coming this way? Does that move that way necessarily or.

Justin Glisan

Not necessarily? That's a that's a good point to say. You look at the high plains and West looks, the map is ugly. East, eastern corn belt been wetter than normal. Now recently we've been drier with this heat dome that's setting in. Drought doesn't pick up and move on its legs. It stays in one area. We look at the south this time of year. If the south is dry, if the south is lacking thunderstorms and they're going through epic flooding down in Texas right now. That moisture gate as it moves north, if it's dry in the southern states, that moisture is extracted as it doesn't get into the upper Midwest. And that's where we get into drought conditions. We're not seeing that right now.

Erin Murphy

Okay. And speaking of that region, I was reading that the Missouri River right now, the flow is significantly low, about half of what it usually is. Tell us what you know about that and the impact that's having.

Justin Glisan

Yeah. So think of barge traffic. More barge traffic on the Mississippi side versus the Missouri side. But the upper basin of the Missouri River is very dry. And we had a lack of snowmelt from winter season. Lack of snowmelt, precipitation deficits, very low flows. And that's where you start to get into problems.

Kay Henderson

I'm wondering if we're approaching some sort of record in the number of severe thunderstorms and maybe the number of tornadoes that have struck in Iowa so far this season.

Justin Glisan

We're about 70 tornadoes year to date. We should be about 42. So we're definitely above average. But we think of 2024, over 130 tornadoes during that season. Record severe weather for much of the upper Midwest in 2024. The observational record here in Iowa, that was the most active severe weather season. So we are above average in terms of severe weather. But luckily we've gotten some rainfall out of that. And if you're not underneath 12 inches of rainfall, it's beneficial rainfall. We've had some crop damage from hail and high winds. We've had one derecho more impactful in Illinois as it formed here in Iowa. But overall, we haven't seen widespread destruction. We haven't seen any fatalities, thankfully. So, yes, it's an active season, but not as active as what we've seen in the past.

Kay Henderson

So let's focus on that derecho for a while. It sort of spun up in Nebraska, and then it did really some significant damage in southwest Iowa, and then it wound up in Illinois, right?

Justin Glisan

Yes.

Kay Henderson

So what can you tell us about that storm and how it would compare to some of the other derechos? I mean, now we've had how many derechos in the past decade?

Justin Glisan

Eight. And you'd have to go back to 2013, prior to the August 10th derecho, which is the record, you know, $13 billion worth of damage here in Iowa. Nowhere near that catastrophic on that derecho. But if you're in that line and you're seeing 80, 90 mile per hour winds. Luckily, it was earlier in the year versus that August 10th derecho when the crop was maturing and standing up in the fields with drought conditions. We had much less damage from that derecho. But we've been in a in a derecho type of pattern. And those heat domes often are the mechanisms that cause those derechos.

Kay Henderson

So again, why has this term become part of our common language when many Iowans had no idea what a derecho was when that one struck in August of 2020?

Justin Glisan

Well, Dr. Hinrichs, back in 1888, termed the the derecho when he was studying tornadic events rotational versus straight line. So it's been in the meteorological lexicon since the late 1800s. But we like to have those sexy headlines, right? Polar vortex, heat dome, ring of fire, derecho. So it's just a way of, of describing weather events in a normal parlance, I suppose. There's also a psychological component to that. When we think about higher straight line winds, more often, we've seen over the last several years. So there's a definition for derecho. It has to meet a certain set of criterion for it to be termed a derecho versus other high wind events.

Erin Murphy

Another one of those terms that's caught fire in the popular lexicon is El Nino. I understand that there's a likelihood we might see one this season and could have impacts reaching into next year. Tell us about that.

Justin Glisan

Definitely. So this has the potential to be a very strong El Nino event. We've had strong El Nino events going back, records starting in 1950, so 1982, 1983, 1997, 1998, 2015 into 2016. So when you look at those strong El Nino events, El Nino is part of a broader pattern in the Pacific called ENSO. The El Nino Southern Oscillation, which is a multidecadal climate pattern in the Pacific. So when you're looking at the phase of El Nino or La Nina has a much higher correlation to weather behavior in the cold season. So right now, the southern hemisphere is in winter. They're seeing broader scale impacts from this potentially strong El Nino. More droughts, more floods, more intensity of extreme events. Whereas in the northern hemisphere summer, it's dictated by mesoscale or thunderstorm driven rainfall. So we're not really seeing the fingerprints of El Nino right now. Where we're looking, though, late fall into winter. If this is a historically strong El Nino, it will have implications on weather patterns. Typically, we see cooler and wetter conditions across the upper Midwest late fall into winter, but also drier and warmer winters. Less snowfall. So if this does develop as a strong, very strong El Nino, and there's an 81% chance that it will be a very strong El Nino, this could be the warmest year on record because more cloud cover in the Pacific locks in that global temperature. And that's where we see a global average temperature that's much above average.

Erin Murphy

What's the range of that impact? I mean, obviously we're here in Iowa, but how widespread is are we talking about here?

Justin Glisan

It'll be mid-latitude globally. So you look at more of Pacific basin westerly flow off the Pacific into the northern hemisphere, into the into North American continent and South America as well. Less of an impact as we move into the Atlantic, into Europe, but it will have broad scale impacts in terms of that global average temperature.

Erin Murphy

And I was going to ask you, but maybe you kind of already answered. You know, for those of us who are detached from the science and the data, like you, we kind of think in terms of what year would that compare to? You listed a few that were historically high. And I was going to ask you, which of those might it be? But you said this could be literally the…

Justin Glisan

Yes, this could be the warmest year on record. It probably will be. You think of the last five years, this has been the warmest five year period for the state of Iowa and for many states in the United States. We've been in a warm decade. We think of the 90s as a very wet decade, the 2020s have been a very warm and a very dry decade. So this is you look at the climate system. Are we seeing changes in the climate system? Definitely. We're leaning more warm and wet.

Erin Murphy

What does that mean? What kind of impacts could that mean for us here in Iowa?

Justin Glisan

So when I say warm and wet, a warmer atmosphere holds more water vapor, but it takes more meteorological loading to produce a weather event like the flooding that we just recently saw just north of here, with the 8 to 12 inches. That's because a warmer atmosphere holding more water vapor, you have to force it more. But once you force it, you get a deluge of that water. Looking forward, these heat domes, these high intensity rainfall events, these persistent droughts only increase in the future. State of the art climate modeling shows that with this warmer atmosphere, we're going to see more extremes. Perhaps less cold extremes in winter, but warmer winters. Warmer winters, 3 to 5 degrees warmer than in the 1970s here in Iowa. Less snowfall, less snowpack on the ground, has implications on snow melt into spring, but also drought conditions. If we don't have snowpack on the ground, deeper frost depth, less moisture as we move into spring, impact on crop going through the growing season. As a person at the Department of Agriculture, we look at these things. Climate services looks at the trends that we're seeing. We can run those climate models backwards and produce extreme events, and they do a pretty good job at running backwards and physically realistic solutions in the atmosphere. This gives us confidence that when we look at projections out several decades, what we're seeing is probably going to happen within a range of possibilities. Climate change is not a black or white thin when you look at the climate modeling. That's why we put a range of solutions in there. But within that range of solutions, we know that extremes are going to become more extreme.

Kay Henderson

You mentioned that you work in the Iowa Department of Agriculture. One of the things that happens once a week is that you are an author of sort of a summary of what's happened in the past week, right below crop conditions. So what can you tell us about standing water and some of the areas of Iowa and how that affects crops? It's more detrimental to soybeans, as I understand it, than to corn.

Justin Glisan

Yes. Soybean don't like wet feet is the is the phrase there. Soybeans in general are more drought resistant, more wetness resistant. But if you have several inches of standing water, if you have a saturated soil profile, you're going to lose yields or you're going to lose that crop if you're in standing water. Corn, a little different. We talked, I was talking with somebody who was driving down the diagonal from Marshalltown last week, and they saw water standing up to the tassels on some of this corn. That's not good for crop. So when you're having saturated soil profiles and you're having heat domes building in, right as pollination is happening, you're going to have yield losses. You're going to have a dent into the yield potential, just given that pollination is not efficient. So these weather extremes, the seed companies have done a good job of hybridization to help mitigate some of these stresses. But they're only going to become more impactful. And that's why climate services are here to provide tools to our farmers and producers to help them pick their hybrids before the season starts, or to help them mitigate some of the damages or the extremes that we're seeing in the climate system.

Kay Henderson

I have some friends who lived on the border of Texas and Louisiana, almost at the Gulf of Mexico, and they had mold in their house. So is this going to create mold on the corn, the ear of corn, mold on the pods?

Justin Glisan

Luckily, we haven't seen a reemergence of southern rust, as we talked about last year, because of the second wettest July on record, a very wet end to July. And that was widespread. And also temperatures were anywhere from 3 to 7 degrees above average across the central part of the United States, with anomalous southerly flow off the Gulf. So we see that as a black swan event. And luckily, southern rust doesn't overwinter. So we started off with a clean slate this season. We have seen conditions that support mold. These wetter or these higher dew points and hotter temperatures. But we haven't seen at least southern rust reemerge here. Other fungal types of infections could occur on the crop, but we're not seeing widespread reports of those.

Erin Murphy

Some of our Midwest neighbors right now, especially Minnesota and my people back in Wisconsin, are dealing with wildfire smoke. Is that, do we know if that's coming Iowa's way?

Justin Glisan

Well, if you look at the heat dome, that's one of the positive points of having the heat dome right over us. It's actually filtering the smoke away from us. It's riding along that ridge. So if that heat dome does stay in play, the wildfires that we're seeing in Ontario, we've seen them year after year after year. It's been dry in Canada. It supports fuel for these forest fires. We think about California. Luckily, we haven't seen widespread forest fires there. But we have seen them in Utah, in Nevada. We have to build into our forecasts and our outlooks that we're going to have wildfire smoke in the upper Midwest at some point in the year and in some part of the Upper Midwest, just given the fuels that are growing to support these wildfires. But as of now, that smoke should stay away from Iowa.

Erin Murphy

And is there a reason that it's sitting and thicker the way it is? And again, maybe this is an anecdotal micro thing. Maybe it's not necessarily more so than in the past. But it seems like in recent years when this has happened, it's slower moving, it's less quick to dilute.

Justin Glisan

A lot of a lot of fire up there, number one. So an excess of smoke up there. We're also in a stagnant flow. The heat dome is sitting over us. Think of a rock and a pond or a stream. Everything goes around it. We're not seeing a lot of steering flow to move broad scale planetary features off. So things just sit. And that's where we see the smoke across the portions of the upper Midwest and in the northeastern states.

Kay Henderson

One of the things I've read is that the jet stream, which, you know, when we were kids, we would see these maps on the TV and they would show us where the jet stream was, is getting wavier.

Justin Glisan

Yes.

Kay Henderson

Number one, why is it getting wavier? And what impact does that have on our weather?

Justin Glisan

Yes. So you think of parking in a parking lot in summertime. You put your visor up. Well, the polar ice cap is our northern hemisphere visor. And we're losing that visor. We call it Arctic amplification. That multiyear sea ice is melting. The perennial sea ice that grows on that multiyear sea ice is melting at a faster rate. The extent of that sea ice is being depleted. More ocean open for absorption of solar radiation, so you're melting the sea ice from the bottom up and top down. The Arctic is warming 2 to 3 times faster than the mid-latitudes. We're also warming here. We're about a degree and a half warmer than the end of the 1800s. You relax that temperature gradient between the mid and upper latitudes, or the higher latitudes, slows the jet stream down more apt to form meanders in the jet stream. And that's where we get into more persistent behavior. A proxy year that I've mentioned before, 2018, wettest year on record across the northern third of Iowa. D-3 drought conditions in southeastern Iowa. Jet stream was locked over the upper Midwest. That's where you see the disturbances just keep going. Deprives the southern part of the state of any moisture. And that's where we get into drought. So you'd only have to move 4 or 5 counties north or south to be in one historic extreme or the other. So expect this in the future. And we're seeing it.

Erin Murphy

You mentioned earlier the flash flooding in Texas. Not exactly an Iowa question here, but it's a national story that we're all watching, reading about. From what I understand, some of this is taking place in a very similar spot to last year. Is that a coincidence? Is there something that scientifically says to you that there's an emerging problem there?

Justin Glisan

The gulf is warm. Lots of evaporation off of the Gulf, lots of moisture being supplied to the southern states. We're also in the monsoon time of year for the desert southwest, getting into hill country in Texas. So when you have drier soils that get saturated and then you have a very fast amount of 1 to 2 inch of rainfall, even three inches per hour, the infrastructure number one can't keep up with that if you're in an urban area. But when you're in hill country, it shunts all that water into one basically basin. And that's where we see continuously these historic flash flood events. And again, we're only going to see more in the future.

Kay Henderson

Give us a forecast. I know you don't have a map behind you. Then a little clicker that you can show everything. But what's the, you know, mid range forecast as farmers think about harvesting in September?

Justin Glisan

Sure. So let's look at the short range because I’d like to give people some hope. It looks like the heat dome will dissolve or dissipate into next week. So back into the 80s towards midweek, lower dew point. As we look, as Erin mentioned, with El Nino, it'll have implications on harvest. If you look at the three month outlooks we are trending slightly cooler than average across the upper Midwest to near normal. So law of averages suggesting end of July into August, we could see cooler temperatures across the state and across the upper Midwest. Thinking about analog years of El Nino, when we look at July, August, September, we have seen cooler temperatures in those three events that I mentioned, but also near normal to slightly wetter conditions as well. Now, when we look at mid to late fall, we have seen cooler and wetter conditions. Now this could have implications on harvest. We don't want to get wet that we can't get harvested. But as we see right now, the higher implications from this very strong El Nino event will come in winter time. So it looks like as a growing season in general, when we look at this strong El Nino event, as we move into the middle to the end of the growing season, it should be less extreme and hopefully less stressful for our farmers.

Kay Henderson

Well, we don't have to stress anymore at this table because this edition of Iowa Press has concluded. Thanks for joining us again.

Justin Glisan

Always a pleasure to be here, Kay.

Kay Henderson

Now just a quick programing note. This is the final edition of Iowa Press for this season. We'll be taking a break because next Friday Iowa PBS crews will be in Fort Dodge to bring you the girls state softball tournament. Then after that, Iowa PBS crews will be getting ready to bring you coverage of the Iowa State Fair, something I know many of you watch. We'll be back here at the Iowa Press table on August 28th. For everyone here at Iowa PBS, thanks for watching today.

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