There have been too many occasions recently that the U.S. has been flying its flags at half-staff. According to USA.gov’s page on the American flag, the U.S. flag flies at half-staff when the nation is in mourning. These periods of mourning occur by Presidential proclamation.
The Wisconsin Department of Military Affairs has a page on Flag-Lowering Orders in Wisconsin. Not only does it give the current flag status and explain under what situations the flag is lowered, it also lists US and state flag lowering proclamations going back to 2009.