00:00May is typically synonymous with severe weather in the plains and parts of the Midwest.
00:05We have had, generally, a near-normal tornado season to this point.
00:11Recently, things flared up quite a bit early in the season.
00:14They quieted down a little bit for the past few days, past week or so.
00:18We've had a couple of brief tornadoes in parts of Florida.
00:21But we're ramping back up in through the end of the weekend and into early next week.
00:25Monday is the day we're most concerned about.
00:27Now, let's take a look at what is going on in the short term.
00:30Friday, we do have some strong storms reemerging into the plains.
00:35And overall, we're concerned about damaging wind and hail for the most part.
00:39The limited tornado risk not quite hitting the threshold that would put us in a spot where we're going to
00:45explicitly list it on the bullet points.
00:47But you're going to notice, as we get into the weekend, the risk is going to begin to escalate.
00:53We have the risk for isolated tornadoes mentioned, damaging wind and hail.
00:56So what's going on here as we step into the next few days?
01:00And why are we highlighting Saturday with a medium risk compared to Friday?
01:04And what goes on on the other side of that?
01:06Things escalate more for Sunday and Monday.
01:08Let's take a look at the models.
01:10This is the motivation behind our forecast here, at least among other things.
01:15Here, we're going to go about 20,000 feet up into the atmosphere, about four miles up.
01:20This is the 500 millibar map, and it's a pretty good general kind of benchmark for the middle of the
01:28atmosphere, at least in the troposphere, the lowest quarter of the atmosphere.
01:33And by volume, that's where most of the weather takes place.
01:36So overall, as we look at the colors here, you can see these bright colors.
01:41These are areas of spin in the atmosphere.
01:44Vorticity is the fancy word for that.
01:47And you can see the flow.
01:48These lines are squeezed together here.
01:51These are thickness lines.
01:52Kind of generally, when the atmosphere is warm, warm air expands.
01:56So we have higher thicknesses when it's cold.
01:59The atmosphere restricts and constricts, and we have lower thicknesses.
02:03So it kind of characterizes the nature of the atmosphere.
02:05You can see these little wind situations here.
02:07Wind barbs indicating the wind speed in knots at that altitude.
02:13So that's the general idea.
02:14But keep in mind, when you see these bright colors, these are little disturbances.
02:19Some of these little sharp disturbances.
02:22Then you see more organized areas with brighter, more vivid colors coinciding with larger troughs.
02:29Sagginess here in the thickness lines.
02:32And those troughs are a little bit more aligned with storm systems.
02:36As you're east of one of those troughs, you're going to have more lift in the atmosphere.
02:39So here's the idea.
02:40A couple of these weak disturbances scoot through the plains over the next day or two, Friday into Saturday.
02:46You can see a slightly more organized trough, even though it's low amplitude.
02:51It's not very deep.
02:52Lifting in through parts of Nebraska on Saturday.
02:56East of there, I'm going to go back to our map here for Saturday.
03:00That's why we're forecasting, if I were to superimpose that trough, again, it's kind of oriented like this.
03:07Early in the afternoon, like this into the night, moving in that fashion.
03:11Areas east of there are where we will see extra lift and extra wind shear, twisting of winds with height.
03:19And that's why we're talking about severe weather on Saturday in that area.
03:22Let's go back to the modeling, and here you can see the overall forecast of where precipitation will occur.
03:28This would be Saturday evening, Nebraska, into Saturday night, moving into eastern South Dakota.
03:33So that's where we're concerned about severe weather here on Saturday evening and Saturday night.
03:37But again, that trough, it's kind of a concise one.
03:41It's well-defined Saturday night.
03:43There it is.
03:44But it's not a very broad trough like what we're seeing out there in Idaho.
03:48Let's go to Sunday.
03:49You can see another one.
03:51This one, a little bit broader, a little bit beefier in a similar area.
03:57And it's a little closer to the core of this broad, long-wave trough moving in through southern parts of
04:05the Great Basin.
04:06So Sunday evening, we become a little more concerned about this storm system.
04:11And you can see it's dynamic.
04:12Look at the west side.
04:13Look at the snow there, accumulating snow in Wyoming, parts of the high ground of Utah, in the interior west,
04:19facing some mountain snow.
04:21Our forecast for severe storms on Sunday, it's kicking up a little bit of a notch here from Saturday.
04:27We introduce the mention of isolated tornadoes.
04:30And remember, it's a little more of a beefier trough.
04:35And Sioux Falls and Sioux City, Omaha, Lincoln.
04:39We're looking at damaging wind, isolated tornadoes, and hail on Sunday.
04:43So Saturday, we've got one threshold.
04:46Sunday, another.
04:47Let's go back to the models.
04:49And we want to go upstairs to see what's going on in the upper-level flow.
04:53And look at this.
04:53Now, the true long-wave trough, the parent system here across the west.
05:00Kind of the granddaddy of them all among this sequence of storms, is going to be moving east.
05:04And as the base of that long-wave trough enters the plains, there's a short wave.
05:10So long-wave, big-picture pattern.
05:12But there's also this little short-wave trough that rounds the base.
05:17Here it is on Monday.
05:19Again, Nebraska is kind of hosting that.
05:22And that's going to amplify the whole trough.
05:26And when it amplifies it in such a way that it gives it more of a northwest to southeast tilt,
05:32that's a negatively tilted trough.
05:33That more aggressively leads to lift in the atmosphere.
05:36So what's that do for our forecast?
05:38Well, here we are.
05:39We're looking at a large area with a moderate risk.
05:41And we suspect, we suspect on Monday, we're going to eventually add somewhere in here,
05:46somewhere in here, a high.
05:48Now, I don't want to commit specifically yet.
05:51We want to, you know, discuss this over the next few days, continue to track the models
05:55and so forth.
05:56But Monday is the day we're most concerned about.
05:58And a few other ways of looking at things.
06:02We're looking at CAPE, convective available potential energy.
06:05This is that contrast between warm, humid air near the ground and much colder, drier air
06:09aloft.
06:10That gets those updrafts going.
06:11There's Friday.
06:14Saturday, kind of a similar magnitude.
06:16Sunday, maybe a step up for Omaha.
06:19Monday, now we're talking about some of these red zones here.
06:23We're getting up around 4,000 joules per kilogram.
06:25And more areas around Kansas City and maybe east of there, beginning to sit up and take
06:31notice.
06:31And when it comes to the significant tornado parameter, we also become concerned about the
06:36risk for tornadoes, not just in the southern plains, but also all the way up into parts
06:40of Iowa.
06:41So that is your forecast feed for now.
06:43Again, the severe threat is going to be escalating Friday, Saturday, Sunday, and Monday.
06:49Stay with us here on the AccuWeather Network.
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