Gas prices in Iowa have increased around 20-cents a gallon in the last 24 hours. Gail Weinholzer, spokesperson for Triple-A Iowa, says unleaded regular fuel is averaging $3.76 a gallon statewide.

“That is 16-cents more than the national average and 23-cents higher than this day last year,” Weinholzer says. Iowa normally has gas prices well below the national average. The sudden rise in gasoline prices across the Upper Midwest is blamed on the closing of two refineries for major repairs.

Weinholzer says the two closed refineries are located near Chicago and are among the biggest in the U.S. One is owned by BP and the other by Exxon Mobile. The refineries are not expected to restart operations until after Memorial Day.

“We probably won’t see price relief until the middle of June at the earliest and perhaps as late as the Fourth of July,” Weinholzer says. “Once a refinery restarts, it takes a while for them to ramp up production.”

It’s not unusual for a refinery to schedule maintenance during the spring or fall switch to new blends of gas, according to Weinholzer.

“What is irregular is that two refineries would close for such an extended period of time,” Weinholzer says. “However, you have to keep in mind that they are owned by two different companies so they don’t sit down, put their calendars side by side, and decide when their respective refineries need to have their maintenance work done.”

Because the refineries are both located in the Chicago area, the price spike in limited to Iowa and surrounding states. “In fact, of the top 10 states in the country for average price, six to seven of them are in the Upper Midwest and Upper Great Lakes region,” Weinholzer says.

She expects gas prices in Iowa will climb even higher by Friday. But, Weinholzer believes prices will remain below $4 a gallon.