The U.S. national average retail price for a gallon of gas is above $2.50 for the first time in months, but the spike might not last, motor club AAA said.

AAA reports a national average price for a gallon of regular unleaded gas Tuesday at $2.55, the first time the national average stayed above the $2.50 mark in more than four months.

"Average prices have now increased by 15 cents per gallon in just two weeks," the motor club said in a weekly report, published Monday. "This recent increase has been the product of rising global crude prices, the seasonal switch to summer-blend gasoline and regional refinery issues, particularly on the West Coast."

South Carolina had the lowest state average with $2.28 per gallon. California had the highest price for Lower 48 states with $3.43 per gallon. At one point last year, more than half of all U.S. states had an average price below the $2 mark.

AAA said an improving crude oil market and preparations by refineries to switch to a summer blend of gasoline, which is more expensive to produce, is in part behind the increase in prices at the pump. The deadline to switch to summer gasoline is May 1 and the shift could make prices could up through spring.

"Following the transition to summer-blend gasoline and as refineries complete seasonal maintenance, the national average may return to below $2.50 per gallon, though much of the forecast will depend on what happens with the cost of crude oil," AAA said.

The national average price for Tuesday is still more than $1 below this date in 2014. Oil prices last year fell more than 50 percent, though have recovered somewhat during the first quarter of the year.