S-Corporations and Partnerships had a deadline of March 15th this year to file their returns or request an extension.  However, because of Winter Storm Stella, which hit portions of the Northeast and Mid-Atlantic, the IRS granted affected businesses an additional 5 days to do so.

Business taxpayers who were victims of the storm, and unable to file their tax return by the due date of March 15, can request an automatic extension (by filing the usual Form 7004) on or before March 20, 2017.  Important tip if filing Form 7004 by paper: eligible taxpayers taking advantage of this relief should write “Winter Storm Stella” on their Form 7004 extension request.  However, the fastest and easiest way to get an extension is still to file this form electronically.

Source: Winter Storm Extension: Many Businesses Have Extra Time to Request A Six-Month Extension