00:00Well, the severe threat is escalating across much of the Midwest here, not just this evening in the
00:06upper Midwest, but especially on Tuesday. We're most concerned about Tuesday, but a tornado watch
00:11has been issued for areas around Minneapolis and into parts of Wisconsin. Severe thunderstorm watch
00:16continues southeast of Chicago through northern Illinois into parts of Indiana and extreme southern
00:22and southwestern Michigan. So let's take a look at this here. We're going to look at a few of our
00:26maps, and then we'll jump over to the computer models just to give you a little more context in
00:32why we're forecasting what we're forecasting. So through this evening and tonight, our risk area
00:39here highlights much of the upper Midwest, places like southern Minnesota, far northern Iowa into
00:45southern and central, really central Wisconsin, with a moderate risk, large hail, isolated tornadoes.
00:50There is a tornado watch box out for much of that area, and then a severe thunderstorm watch also
00:55is in effect for area south and southeast of Chicago as well. And tonight's risk zone includes
01:00Minneapolis and Rochester, Minnesota, Eau Claire, Wisconsin, Madison, Wisconsin, with that hail,
01:06isolated tornado, and wind gust threat. That's the concern in the short term. In the short term,
01:12as we look at the models here, this is being driven largely by a disturbance that has been emerging
01:17across the upper part of the plains, the northern plains. That short wave here is going to be
01:24lifting up into parts of the Midwest. And even in advance of that, there has been some extra noise
01:30here among weaker vorticity maximum. Vorticity is a measure of spin in the atmosphere. And if you're
01:37northeast of one of them, we're dealing with an area where there's going to be extra lift in the
01:42atmosphere. That coupled with warmth and humidity near the ground, colder air upstairs, they all work
01:47together to produce these severe weather events. But take a look at Tuesday. This is when a stronger
01:53short wave emerges. And this is tied to what was once that California storm system. You can see it's
02:01a chunk of vorticity tied to a big lobe of energy over the interior northwest. And it can be also
02:07attached to that trough in a large scale fashion, attached to the California low pressure system.
02:13That's what ejects across the Rockies and reaches the plains. And if you're east of that,
02:18that's where you have more lift in the atmosphere here tomorrow evening and tomorrow night.
02:22So that's all a big concern. And then that carries through the Midwest into Wednesday,
02:26but it weakens a bit as it does that. So when we look at the forecast printouts here from the
02:33computer modeling for precipitation, you can see some heavy thunderstorms in the upper Midwest here this
02:38evening and tonight, even near Chicago. And then in a Tuesday, that expands. We're looking at a lot
02:43of snowmelt coupled with this. There's some deep snow on the ground up in northern Michigan.
02:47So stream and creek flooding will be a concern as this all moves through that area as well. But a
02:51new episode late Tuesday breaks out. And again, in this depiction, they look kind of similar.
02:57But overall, the storms here that I'm highlighting, they're going to be a little more aggressive.
03:02And I'll show you why here in a minute. Again, it's partly fueled by that jet stream energy coming
03:09across the southern Rockies and entering the plains from what was once that California storm.
03:13But when we look at instability, convective available potential energy, it's an acronym,
03:18CAPE, we call it. And this is the current set up here this evening, where we have relatively strong
03:23CAPE, not off the charts, but moderately strong amounts of fuel, warmth and low level humidity
03:30under high up there in the atmosphere under some colder air aloft. That contrast between the warmth
03:39and humidity at the ground and colder air aloft allows for these parcels, these bubbles of rising
03:46and lifting air to continue to rise if they're more buoyant and warmer than surrounding air.
03:51You'll notice on Tuesday, some of the modeling, especially the, here's the NAMM, that produces some
03:57pretty more, slightly more impressive CAPE into the Midwest on Tuesday afternoon and into the
04:03evening through Chicago. Here's the European model. Today, modest. Tomorrow, similar, but again,
04:10somewhat more significant wind energy aloft. It's the GFS that produces a slightly stronger signal
04:17compared to today, where it's a little bit more meek in areas near Chicago. It increases in Chicago.
04:22But another thing to look at is this energy helicity index. So this is combining CAPE, but it's also
04:30accounting for something called helicity. If you picture maybe a spiraling football and you trace
04:36the path that the, maybe the laces take, this spiraling fashion. And here we're looking at how there is
04:44some extra wind shear and helicity in the low to mid levels of the atmosphere, especially low levels of
04:50the atmosphere here. And when you combine twisting of winds with height, they give us extra helicity
04:55and also that lift in the atmosphere. You can see that we're highlighting areas where there's
05:01some helicity out there, some tornado potential in Southeast Kansas, Northeast Oklahoma today.
05:06But tomorrow, the Chicago area steps into view here. Here's another depiction, the NAMM today,
05:11tonight, and then tomorrow it ramps up near Chicago, the third biggest city in the country.
05:15So that's a concern. Because of that, I'm going to go back to our maps. We are highlighting for
05:22Tuesday, a high risk. That's three out of four on the AccuWeather four tiered severe threat index
05:28for areas around Eastern Iowa, Southern Wisconsin, and far Northern Illinois, including Rockford and
05:34Chicago. So here we have our severe threats in this meter fashion, wind and hail, a high risk of those
05:41concerns in parts of the Midwest, and a medium risk of tornadoes. That's pretty significant.
05:46Let's take a look at our in-house model and how it depicts things for Chicago. A high risk of
05:52wind
05:52and hail. Here we are pressing pause at 8 p.m. We don't want to take the specifics, specific placement
05:58of these thunderstorms too literally, but we do see the message here. Near and south of Chicago,
06:04the risk is significant here. And then also up to the Northwest, the risk is significant. And then
06:09through the overnight hours, we're going to have storms of probably a different character move
06:12through the area with heavy rain and a flood threat then as well. So here it is again, as we
06:18go through
06:18the evening. So the Tuesday evening into the overnight timeframe, we have big concerns for Chicago.
06:23After that, the storm threat is still present in a large area for Wednesday, but it comes down a notch
06:30here as overall the Jetstream Energy aloft for Wednesday. It's still present, but the amount
06:39of CAPE is a little bit more limited. And again, the Jetstream Energy will be driving some severe
06:45threats even into midweek. But Tuesday is the bigger day we're most concerned about.
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