The actual advisory from the FAA is:

ATCSCC Advisory
ATCSCC 111 DCC 11/13/2026 NATIONAL GROUND STOP
MESSAGE:  	

EVENT TIME: 13/2053 - 14/0400
DUE TO EXTRAORDINARY CIRCUMSTANCES AND FOR REASONS OF SAFETY.
ATTENTION ALL AIRCRAFT OPERATORS, BY ORDER OF THE FEDERAL AVIATION
COMMAND CENTER ALL AIRPORTS ARE GROUND STOPPED. ALL DEPARTING
TRAFFIC SHOULD REMAIN GROUND STOPPED UNTIL FURTHER NOTICE. INBOUND
INTERNATIONAL FLIGHTS WILL BE MANAGED ON A CASE BY CASE BASIS. 

EFFECTIVE TIME:  	132054 - 140430
SIGNATURE:  	26/11/13 20:54  

Source: https://www.fly.faa.gov/ois/oisedit/adv_oisedit_dis?number=111&day=11132026&gdp=-1&gstop=196093

Beyond that, all I've seen so far is:

Markwayne Mullin, the secretary of homeland security, says Trump administration officials blamed a telecommunication outage but said they did not know its cause and that it would “take some time” to fix the issues grounding flights.

per NYT's reporting: https://www.nytimes.com/live/2026/11/13/us/ground-stop-nationwide-flights-faa/d2ae2ce1-ac6b-59ad-ad8d-daef4e181b34

Edit (longer quote further down from Mullin):

Markwayne Mullin, the secretary of homeland security, blamed the ground stop on a telecommunication outage but said Trump administration officials did not know the cause, adding that it would take an extended period of time to fix the issues. “This isn’t going to just be resolved and turned around within the hour,” he said. “This is going to take some time.”