Average gasoline prices have jumped for a second straight week as oil prices have climbed back above $60 a barrel. New sanctions on Iran's oil are making it more difficult for those barrels to reach the market, tightening supply. Also, a major winter storm that sent temperatures plunging is also likely to impact refineries, causing disruptions and reducing output. Diesel prices have jumped as colder weather boosts demand for heating oil. Gas Buddy says it expects both gasoline and diesel prices to rise in the week ahead. Average gasoline prices in Minnesota have risen 6.4 cents per gallon in the last week, averaging $2.69 a gallon. The national average price of gasoline has risen 7.6 cents per gallon, averaging $2.84. The national average price of diesel has increased 7.8 cents compared to a week ago and stands at $3.54 per gallon.