The Mississippi River is known as the Middle Mississippi from the Upper Mississippi River's confluence with the Missouri River at St. Louis, Missouri, for 190 miles (310 km) to its confluence with the Ohio River at Cairo, Illinois. The Middle Mississippi is relatively free-flowing.
As Hopper notes, eight major U.S. airlines offer free cancellation for tickets purchased at least seven days in advance: Delta, United, US Airways, JetBlue, Southwest, Spirit, Frontier and American (in American 's case, you'll hold your ticket instead of purchasing it).
Cancelled flights. Where your flight is cancelled, you are entitled to a choice of: Refund of the cost of your ticket within 7 days or; Re-routing to your final destination at the earliest opportunity or; Re-routing at a later date at your convenience, subject to availability of seats; You may also be entitled to compensation.