Severe storms in the Great Lakes area and extreme heat in the Plains this week are actually directly related. AccuWeather's Bernie Rayno breaks down how that connection works.
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00:00 The threat for nocturnal storms increases this week in parts of the country.
00:04 These are thunderstorms that happen after the sun goes down, which can make them even
00:07 more dangerous.
00:08 Bernie Rayno takes a closer look.
00:10 Well, in our weather-wise segment tonight, we're talking about nocturnal thunderstorms.
00:15 It's a fascinating process.
00:18 Unfortunately, it produces lots of weather, damaging winds and also flash flooding.
00:22 We saw that during the overnight period last night across Michigan and Ohio.
00:27 We're going to get it again tonight, and it always occurs on the northern side of heat.
00:32 It depends where your upper-level high is located.
00:34 Now, the last 24 hours, that high has been across Oklahoma.
00:39 What happens is you build the heat, you build the heat all afternoon hours, and then that
00:44 heat is transported on the northern side of high pressure northward.
00:49 Then that heat continues to come northward, and then when it intersects where you have
00:53 northwesterly flow aloft, that's where the showers and thunderstorms occur, because what's
00:58 happening?
00:59 That northwesterly flow aloft is bringing cool air down.
01:02 So, warm at the surface, cold air aloft, same situation you get during the afternoon when
01:07 you get the heating of the sun, right?
01:09 It's just a different process.
01:10 Now, here's how it works.
01:12 Typically, we don't get these thunderstorms in the afternoon.
01:14 You know why?
01:15 Because the sun's out, it's warming the cloud tops or warming the upper atmosphere, and
01:20 you don't have a big enough temperature difference between the surface and aloft to get the instability
01:24 to produce the thunderstorms.
01:26 But then what happens at night?
01:27 You lose the sun, you continue to bring that northwesterly flow down, right?
01:31 Bringing in the cool air aloft, you don't have the sun, you start cooling the upper
01:36 levels, but then here comes the heat that builds up during the day.
01:38 That makes for a very unstable environment, and then the showers and thunderstorms blossom.
01:43 They tend to peak after midnight.
01:46 But then what happens in the late morning?
01:48 Well, the sun comes out.
01:49 You start heating the cloud tops.
01:51 You start warming things.
01:52 You use that temperature difference, and then the clusters of showers and thunderstorms
01:56 dissipate.
01:57 That's the life of these nocturnal thunderstorms.
02:00 And as I mentioned, with all the heat that's trying to come northward and eastward across
02:04 Ohio and Pennsylvania, look for another cluster of thunderstorms late tonight across parts
02:09 of Pennsylvania and New York State.
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