there is some debate as to the legality of this declaration. the relevant law says the emergency has to have "actually occurred" instead of being expected
(1) The provisions of this section shall be operative only during the existence of a state of emergency (referred to in this section as "emergency"). The existence of an emergency may be proclaimed by the governor or by resolution of the legislature, if the governor in his proclamation, or the legislature in its resolution, finds that a natural or man-made disaster of major proportions has actually occurred within this state, and that the safety and welfare of the inhabitants of this state require an invocation of the provisions of this section;
Yes, seems like it is something that you declare in response to a disaster, not in order to prevent one. Perhaps the disaster is the state of policing in the US.