Update. It has been raining south of Albany, NY for the past week at night. This evening it is clearish (Jupiter and Arcturus visible) and the fireflies are no longer flashing.
http://hymfiles.biosci.ohio-state.edu/projects/FFiles/frfact.html
"If you live in the United States, west of about the middle of Kansas, you are not apt to have the flashing type of fireflies in your area. Although some isolated sightings of luminous fireflies have been reported from time to time from regions of the western U.S., fireflies that glow are typically not found west of Kansas. The reason for this phenomenon is not known."