There's no alert, but you can find updates here: https://www.southwest.com/air/flight-schedules/index.html They usually post the next schedule extension date shortly after an extension occurs. Currently the site says "We are currently accepting air reservations through June 5, 2018. On November 2, 2017 we will open our schedule for sale through August 12, 2018. This date is subject to change! Please check back frequently."
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