WTF? First class mail over 13ozs.
IS Priority Mail:
General Information
First-Class Mail is the least expensive, most immediate option for mailing postcards, letters, and large envelopes 13 ounces or less. First-Class mail over 13 ounces is called Priority Mail®.
Prices based on shape and weight
First-Class Mail is closed against inspection. (The United States Postal Service® may open mail classes other than First-Class Mail to determine if the proper postage was paid.)
Estimated delivery time is two (2) to three (3) postal business days and begins on the date postmarked. In some instances (short distance between ZIP Codes™), it is possible for delivery to occur in one day. First-Class mail is not a guaranteed service. Delivery by a specific date at a specific time is not available.
Not sure if it applies but read the last bulleted question on this page:
http://tinyurl.com/27tj69z