Joe Keith runs to his truck as it rains in Collinsville July 19. MIKE SIMONS/Tulsa World
Those who have lived in this area know the summer climate: It’s hot and it’s dry.
This summer is no exception, other than that it may be a little hotter and a little drier than usual. After last summer, this marginally-worse-than-average summer just seems like a vacation.
But just because it’s our dry season doesn’t mean it’s completely void of rain. It does happen, but the storms we see are usually different than storms we would see in the spring.
That’s what happened last week. Dark clouds on Thursday brought rain to the Tulsa area, but they exploded and dissipated, meandered generally in one direction, but kind of aimlessly. Those are different from typical spring storms, which strengthen and move with purpose.
Colloquially, they’re called
popcorn storms. The isolated storms explode quickly on radar, are generally unorganized kernels of big, white clouds that dissipate quickly.
Technically, it’s an air mass thunderstorm. Karen Hatfield, meteorologist with the National Weather Service office in Tulsa, tells me that it’s all about how they are formed that distinguishes the popcorn storms from typical spring storms.
“Springtime storms usually develop in response to a boundary of some sort (a front, dryline, outflow boundary, etc.), an upper level storm system, or a low level jet. In the spring, there is typically enough shear (wind speed variation) in the atmosphere to give storms time to develop and persist before they dissipate, and therefore, their severity is usually a little easier to determine with more lead time.
Thermodynamically forced storms in the summertime, however, develop in response to a hot, humid atmosphere with little in the way of dynamic forcing. Daytime heating allows temperatures to reach the "magic" convective temperature (the temperature at which low level air can rise without being "stopped" before becoming a thunderstorm), which is why they are typically tied to the diurnal heating cycle (i.e. - develop during the afternoon and dissipate with sunset).”
Make sense? Cool.
Look at these two screen shots I took from the radar on my phone. On the left are popcorn storms about three weeks ago. On the right is a line of severe thunderstorms associated with a dryline moving across Texas and Oklahoma earlier this spring.
It’s hard to tell on a screen shot but with movement, the storms on the left were disorganized and slow, with movement that is atypical of springtime storms. On the right was an organized squall line of fast-moving severe thunderstorms.
That’s something else that makes summer storms different: Typically, they are below severe limits. While they may have strong downbursts winds and small hail, it’s usually not enough to issue warnings.
Because the storms tend to form quickly, die off and merge without the observable dynamic factors associated with spring storms, they can be hard for forecasters to predict where they will form.
“There is usually very little shear in the atmosphere during a typical summertime situation, causing storms to both move very slowly and collapse very quickly; this latter point is what makes it difficult to gauge their severity and lead times are typically smaller,” Hatfield told me.
On July 13, a cluster of storms with those properties came through the area. An example of their isolated nature can be seen in rainfall totals: Tulsa International recorded 0.08 inches of rain that day, while Tulsa Riverside Airport recorded 0.92 inches. That’s a wide difference between the two that aren’t that geographically far apart.
For people in the Jenks area, that rainfall can be a boon, especially when it is so dry. But these storms are so isolated they won’t do much to bust the drought. Temporary relief at best will be sucked up into the atmosphere the next day when temperatures climb back to 100.
There is a strong chance of rain Thursday and Thursday night. Right now it’s at 50 percent, which is one of the highest chances of rain I’ve seen so far this month. It will be associated with a cold (HA) front plunging south thanks to a weakened high pressure system that typically keeps storms north of us.
