(Des Moines, IA) -- Iowa crops and gardens in the Des Moines area and northern Iowa might be at risk. A freeze advisory will be in effect Friday morning in Des Moines metro and southwest Iowa. A freeze warning will also be in effect north of I-80 around Ames. The National Weather Service says temperatures as low as 33 will result in frost formation and it could kill sensitive outdoor vegetation if left uncovered. The NWS has issued the advisory for overnight from 1:00 A.M. to 9:00 A.M. Friday. Unprotected plumbing could also be at risk.