����vlog

Hi there, our meteorologist Trey Fulbright and today we will be talking about hail in central Iowa. We're gonna talk about how it forms. We're also gonna look at how it looks on radar when we're interpreting it. And we're gonna look at some uh state hail frequency and climatology. And then finally, uh answer *** question that I got on one of my Facebook pages last week. Why have we seen so much hail this year? Uh So first off here, we're gonna look at some of the top hail ingredients because I think it's first *** good idea to get on *** good understanding of how hail forms. So that when we look at why we've seen this much this year, uh then we can see these ingredients kind of line up and that'll kind of explain why we've seen so much hail. So one of the first things we look for obviously is *** thunderstorm. You need *** thunderstorm with *** powerful updraft to get hailed. Uh but it's not just any thunderstorm, we have to have *** severe thunderstorm. And in order to get those, we look for three things here, we look for large amounts of potential energy and meteorology. We call this cape and that stands for convective available potential energy of the larger your cape. That's more, more fuel essentially that's available for *** storm up draft to grow and grow explosively. And uh the longer live that storm up draft lasts the more severe it can become next up here. We also look for strong winds aloft but the winds down low near the surface are winds that are typically weaker. We call this speed sheer when the winds increase speed with height but not necessarily change *** lot of direction. What that speed sheer does? It helps to separate your thunderstorm regions. You have *** part of *** thunderstorm where the air currents are going up, we call that the updraft and then the part where the air currents are sinking, that is the thunderstorm downdraft and so speed, she allows for our thunderstorms to be *** little more tilted so that those two regions stay separate when those two regions stay separate. Then the water droplets that are carried up into the thunderstorm cloud can then persist or last *** little bit longer due to the speed sheer that's in place and then they freeze and then that process keeps repeating and allows for those hailstones to form and grow. And then finally, we look for *** very cold atmosphere as well because obviously we want the part of the atmosphere where our hailstones are forming, it has to be below freezing. And so we want *** good portion of the cloud depth to be in that part of the atmosphere where it's below freezing so that hail can accumulate and grow more effectively. So this is kind of *** visual here of how the uh updraft looks that hail formation process inside the thunderstorm. So we have our raindrops that become frozen as they're sweat up by the updrafts. And so as those raindrops move above the freezing level, then layers of ice begin to form around those raindrops. So you start out with *** small hailstone, but then as it encounters more layers of water or more layers of, of water that forms layers of ice. And so eventually those keep growing until your hailstone becomes larger and larger. Uh oftentimes when you see *** hailstone, you might see the rings around it if you cut it in half. And so that's an indication of how many times that hailstone has received *** new layer of water to freeze on it. And then eventually, when our hailstones become too large, when uh the weight of the hailstone exceeds the force of the updraft, then that hailstone falls back down to the surface. And uh that's when you start to feel the impact down low. So obviously, when we have bigger hailstones, that means those hailstones have stayed in the clouds longer and then they've been carried by *** stronger updraft to allow those to persist longer. This is *** look at how hail looks on radar uh on radar when we're looking at hail, one of the first things we look at is reflectivity that basically shows how strong or how intense is an echo being portrayed on the radar. So we look for obviously these more intense colors on here where you see some of the reds, pinks, uh blues and whites on our radar system here at K C C I, it's color coded for pink, uh gray, black and white to show some of the stronger returns. All this simply means is that the radar is detecting very large targets and targets that are highly, highly reflective. Well, hail is larger than *** raindrop. So it's gonna be much, uh it's gonna show up much more easily and it's also reflective as well, especially if it's coated in *** layer of water. So it sends *** really strong signal back to the radar. And that's why we see these very bright colors uh when we're looking at it on radar and then you'll note here extending off to the southwest of this thunderstorm here, uh this region of this that looks like precipitation, uh that's not precipitation though, that is an artifact of hail. And we call that *** hail spike or *** three body scatter spike. The reason why we call it that is because as the uh radar beam sends energy out and it hits the hail storm or hits the hailstone, there's so much energy that's being brought back to the radar, that part of that energy gets deflected down to the ground, back up to the hailstone and then it goes out in another direction. That's why we call it *** hail spike because that energy is being deflected in three different ways there. So that's one of the ways we look for hail on radar. And there are *** whole lot of other tools and uh uh products that we use behind the scenes here as well to really infer and uh confirm if there's hail actually occurring. Now, let's talk about hail climatology here in central Iowa. We'll look at hail reports by month and this data goes back to 2003. I downloaded this uh data from the central Iowa region here, roughly the middle third of the state and as obvious and obviously, as one would expect our peak hail months here are during the spring, April May and June with June coming in as the having the highest number of hail reports since 2003. So we are definitely not out of our severe storm season just yet. And then ultimately, those reports start to slide back down as we move closer to the end of the year. Now, we'll look at hail reports by year here and you can see the numbers here can fluctuate depending on how active our severe storm season is. Ranging anywhere from as low as 41 reports of severe hail in 2016 to as much as 396 reports back in the very active year of 2004. And, uh, you can see some of our more active years, uh, come when we have, when we have *** little bit more favorable pattern for severe weather and times we'll look for La Nina, which is basically *** cooling of the East Pacific Sea surface temperatures that can kind of enhance the jet stream and create *** little more favorable environment for severe storms around here. That's one of the things we look for, maybe for an active year, but there are *** whole lot of other factors as well that can drive these numbers and these reports up. So we'll look at hail reports by county here. This is across the state. And as you would expect, most of the hall reports that come in are obviously over some of our more populated counties here over Polk and story counties uh with fewer reports outside of that region. But if you were to kind of uh take out those uh more populated counties here of central Iowa, you would see kind of *** general trend to have more hail reports over our western and northern counties. Again, if you, if you just kind of excluded all the, if you took out that population bias, you would see more, more hail reports generally again in our western and northern zones, then we'll also look at the largest hail observed by county and remember these reports go back to 2003. So out of the data set that we have available here, uh hail reports go back to 2003 and you can see the two largest reports of hail to come in for our region here. 22 reports of 5.5 inch in diameter hail here which is bigger than softballs, it's bigger than grapefruit. Uh We had *** report of that in Story County and one in Hancock County. Both of those came on the same day as *** matter of fact, back in 2004. So as I mentioned, 2004 was *** very big hail year here across the state. And now let's talk about why have we seen so much hail this year? Well, go back to what we talked about early on the ingredients that we need for hail storms to form. And then we'll look at some of our most active severe weather days so far. If you remember, we had that big event on March 31st, that was part of *** large scale severe weather outbreak, including multiple tornadoes that uh tore through the eastern half of the state and then down into the deep south, uh April 4th, just *** few days later, that was *** really big hail event. And then here recently May 7th, very large hail went across parts of Jasper and the Palaic counties here. Those were two of our harder hit areas. But what was common on all these days that drove up our hail reports so far this year. Well, one of the things uh that we saw the storm mode that day featured super cell thunderstorms. Super cells are some of the most powerful thunderstorms with the most uh prolonged updrafts and they're also rotating. And in the super self thunderstorm, you need an environment that has *** lot of speeds here. Remember we talked about speed here uh where the wind speed increases with height in the atmosphere and allows your storm to kind of stay up uh to uh to tilt and then have the updraft and downdraft region separated. And so that allows for more residents time for your hailstone to stay within the cloud and to grow and get more layers of ice on it to become larger. So we have that going for us on all of these events and then uh looking at more the fuel or the background picture in terms of uh the the available energy in the environment, we have lots of that as well. We had lots of cape on those days and also something else to note, looking at observations, looking at data from weather balloons launched nearby. Uh we had *** dry middle level of the atmosphere and that's very important when we're talking about hail formation because when the middle levels of the atmosphere are dry, that allows for it to cool faster. So, uh we had *** very low freezing level on *** lot of these days as well. So as the hail uh moved up into the clouds, it had *** large region where it was below freezing in the clouds. So the ice, so the water droplets could last longer and essentially grow into more and larger stones. So that's kind of *** look at how we get hail and why we've seen much hail so far. This year, we've had *** lot of the ingredients favoring hail storms here across central Iowa. So I hope you enjoyed this weather brief and, uh, continue to stay up to date as we move through the core of our severe weather season here with K C C I.