The power of preemption is derived from

n. the rule of law that if the federal government through Congress has enacted legislation on a subject matter it shall becontrolling over state laws and/or preclude the state from enacting laws on the same subject if Congress has specificallystated it has "occupied the field." If Congress has not clearly claimed preemption, a federal or state court may decide theissue on the basis of history of the legislation (debate in Congress) and practice. Example: Federal standards of meat orother products have preempted state laws. However, federal and state legislation on narcotics control may parallel eachother.

they encountered severe weather for which they were poorly prepared.