This week on Science Behind the Forecast, learn how pop-up thunderstorms form s LPM’s Bill Burton talks with meteorologist Tawana Andrew.
This transcript was edited for clarity and length.
Tawana Andrew: We’re talking about a stereotypical part of our summer weather.
Bill Burton: Something that can pop up out of nowhere-and it’s got me hungry for popcorn. We’re talking about pop-up thunderstorms. What do we need to know?
TA: It’s very easy to forecast the possibility of those storms, but predicting exactly where and when a pop-up thunderstorm will occur is a lot more difficult. You kind of have to be a magician to do it, basically. On a summer day, you have plenty of moisture, plenty of heat available to form clouds and to fuel thunderstorms. That energy and fuel are most plentiful in the hottest part of the day, which is usually the afternoon, hence the afternoon pop-up storms that we typically see.
Sunshine heats the ground, warming the air right above the Earth’s surface, and some areas will heat more than others. Asphalt is going to heat a lot more than grass, and concrete is going to heat a little bit more than a park will. That differential in heating creates boundaries where air begins to rise and form clouds. Warmer air in general will hold more moisture, and that warm rising air provides plenty of fuel for a cloud to form, and then eventually a thunderstorm. We just watch how temperatures rise, and that continued heating creates those cumulonimbus clouds, aka thunderstorm clouds.
BB: You’ve got to have that energy to make all of this happen, right?
TA: Right. That’s why you tend to see more of those pop-up storms on those hotter days, especially those hot, muggy days. On some days, cumulus clouds are kind of like popcorn kernels. They need the right amount of heat and energy to pop into a thunderstorm.
BB: You have my attention.
TA: I figured I would. Once the storm’s updraft reaches a level in the atmosphere where it can no longer rise, the air begins to cool. The raindrops become too heavy to continue upward, and eventually the rain will fall. You will have that cooler air rushing towards the ground, creating gusty winds at the surface. But just like in a bag of microwave popcorn, some of those kernels never pop. They’re just kind of stuck there staring at you. While others will fire into delicious popcorn or not so delicious thunderstorms with heavy rain, gusty winds, lightning, and small hail.
BB: So the ones that don’t pop, they just sort of dissipate?
TA: They kind of just stay there as pretty cumulus clouds, and eventually fade once we lose the heating of the day. The heating of the day is a big part of this because once the sun sets, the lack of heat removes the storm’s fuel, and then those storms will all dissipate. Before we get to that point, sometimes the storms will just rain themselves out, and then you just end up with a muggier afternoon. But yeah, summer pop-up storms are a typical part of summer weather. And hey, we just have to keep an eye on the radar as we head through the summer months, and keep an eye on those temperatures too.
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