Commonsense Legislative Exceptional Events Reforms Act of 2014 - Amends the Clean Air Act to revise the requirements for regulations that govern the review and handling of air quality monitoring data influenced by exceptional events. (The Environmental Protection Agency [EPA] may exclude monitored exceedances of the National Ambient Air Quality Standards from consideration when designating an area as nonattainment, redesignating an area as nonattainment, or reclassifying an existing nonattainment area to a higher classification if a state demonstrates that an exceptional event caused the exceedances.)

Requires the criteria used to determine if an exceptional event was demonstrated to be specific in order to minimize the discretion of the EPA in approving or disapproving the demonstration.

Requires the EPA to make a determination within 90 days after the submission of a petition by a state of an exceptional event demonstration. Considers the demonstration approved if the EPA does not make a determination by that deadline.

Requires a determination to be based on a preponderance of the evidence and to accord substantial deference to the findings of the state exceptional event demonstration. Establishes an appeal process for reviewing a disapproval of a demonstration.