Gas prices continue to jump as stations make the final change to summer-blend fuels and an increased driving season takes hold. According to a news release from AAA Mid-Atlantic, Friday’s national average price for a gallon of regular unleaded gasoline was $2.41 — three cents more expensive than one week ago, 12 cents more than one month ago and 31 cents more than one year ago. The Kroger on Commonwealth Boulevard has the lowest price in Martinsville at $1.99. The Marathon’s on Commonwealth and on the Greensboro Road were next at $2.05 a gallon. The national average is at its highest level in 19 months, according to AAA.