Early hot temps to subside, official says

On Wednesday, temperatures surpassed 90 degrees in Cape Girardeau.

According to the National Weather Service, it was the earliest 90-degree day since 2012; not just for Cape Girardeau, but also for other cities in the region.

Sean Poulos of the National Weather Service (NWS) Paducah, Kentucky, office remembered the oppressive and unseasonable conditions from a decade prior.

Although Poulos has been a meteorologist with NWS for nearly eight years, he couldn't feel the unusual heat until he mowed the lawn after his workday Wednesday.

"It was uncomfortable. I definitely worked up quite a sweat. It felt more like the middle of July or August than it did May 11th," Poulos recalled.

Exactly what's causing the weather is harder to say. Right now, Poulos explained, there are dramatic windcurrents some 20,000 feet above ground that aren't necessarily evident below.

"Miles above the surface, basically, and they have kind of dug down like a funnel," Poulos said.

These powerful forces have drawn air from the Gulf of Mexico farther north than usual, up into Southeast Missouri and beyond.

"The air that would typically be in the southern U.S. has been brought up into our area, even as far as the Great Lakes," Poulos said. "So, areas that don't typically see 90-degree weather this early in the season are now having it. They are feeling what has typically been southern weather patterns."

Poulos said the meteorological term for this culprit is "upper-level ridge." He said the ridge has "centered overhead" and is "very unseasonably strong for this early in the season."

"It's pumping out this weather, allowing a dry air mass to create temperatures into the 90s. That's not unheard of for May, but for this early it's rather uncommon," Poulos said. "Usually we don't see this type of air mass get settled into the area until maybe Memorial Day."

The discomfort of heat and extra waterings in the garden aren't the only things the unusual heat can generate, though. Severe weather events can be more likely under a condition meteorologists refer to as "instability."

According to w1.weather.gov, "Instability is a prerequisite for severe weather -- the greater the instability, the greater the potential for severe thunderstorms."

"Warm air typically does create more instability. Especially as the humidity increases and you get moisture in that warm air, the instability increases as well. When we have this type of air mass, which does seem to be occurring a little bit more frequently, that does seem to result in stronger thunderstorms which, may in turn, develop tornadoes," Poulos elaborated.

Derechos, large wind events potentially more destructive than a tornado with winds stronger than a hurricane's, are similarly common in late spring and summer, when high pressure weather systems are most likely. Derechos ravaged areas of Missouri in July of 2018 and April of 2020.

For the moment, however, isolated thunderstorms are the extent of what has been predicted for this weekend, with temperatures expected to fall back into the 80s next week.