Powering America for Tomorrow Act - Amends the Federal Power Act to direct the Federal Energy Regulatory Commission (FERC) to designate one or more regions within the Eastern Interconnection and the Western Interconnection to be represented by specified regional transmission planners.

Sets forth application and approval procedures for regional transmission planners.

Prescribes: (1) a regional transmission plan design, and (2) a regional transmission planning process.

Requires the federal power marketing administrations and transmitting utilities in a designated region to integrate their transmission plans with the regional transmission plans required under this Act, and to otherwise participate in a regional transmission planning process.

Directs FERC to require that: (1) all regional high voltage electric transmission cost allocation processes and methodologies adhere to a clear and consistent set of specified regulatory principles, and (2) regional transmission planners coordinate planning across regional boundaries within an Interconnection.

Authorizes a regional transmission planner, as part of a plan submitted to FERC, to identify regional transmission projects required by, and consistent with, the public convenience and necessity.

Directs FERC, in issuing a certificate of public convenience and necessity, to give substantial deference to any proposed finding of public convenience and necessity in the plan submitted by a regional transmission planner.

Excludes from review for any environmental assessment or environmental impact statement required under the National Environmental Policy Act of 1969 any proposed finding by a regional transmission planner of public convenience and necessity with respect to a regional transmission project.

Retains state exclusive authority over the siting of any transmission facility that is not a part of a regional transmission project.

Specifies federal siting authority with respect to any transmission facility identified as part or all of a regional transmission project for which a certificate of public convenience and necessity has been issued.