Average temperatures this August in Iowa have recently been cooler than usual because of a more active air current called the jet stream.
Over several days in the last week, cloud cover and rainfall kept daytime temperatures at most five degrees cooler than the average of 71 across the state, according to the state’s Climatology Bureau.
State Climatologist Justin Glisan says the jet stream dipped, resulting in lower temperatures.
“When you have the jet stream behavior – when you have a more active pattern like this, you do get cooler air that filters into the region,” Glisan said.
Glisan says around this time of year the average overnight low is 61 degrees, but temperatures were slightly below that as well. High temperatures will be back in the 90s in some parts of the state as early as Saturday.
Features in a more active jet stream can also cause temperatures to swing back and forth, Glisan said.
From May to July this year, the jet stream was further north than normal, bringing lots of rain to northern Iowa. The rain missed southern Iowa, which has been in a drought.
“These low-pressure systems are like boats in the stream,” Glisan said. “Depending on where the stream flows, that’s where the boat goes.”
But as fall approaches, the more active jet stream will move further south, creating “a better distribution of rainfall,” he said.