Iowans need to start paying more attention for the sound of an oncoming locomotive — especially if there aren’t train tracks nearby. Today is the start of Tornado Awareness Week. National Weather Service officials want to educate Iowans about one risk of living in this part of the Midwest.Brenda Brock is meteorologist-in-charge of the National Weather Service office in Johnston, near Des Moines.While Iowa averages 35 tornadoes a year, there were 59 twisters last year and more than 70 the year before. Two Iowans were killed by tornadoes in Harrison County last year, the first twister deaths here in 13 years. There were also 28 injuries reported — the average is 29 injuries a year.Already 18 Americans have been killed by tornadoes this year — though no twisters have yet hit the Hawkeye State. Brock says they’re most likely during the months of April, May and June.