M3 appears to be a hazy patch halfway between Arcturus and Cor Coroli, about one sky arc minute in diameter.  Moon has not risen, so that made it easier to spot.  By defocussing the binoculars a little, I made other stars in the field the same size as M3, and picked one of similar brightness (circled).  The star I picked turned out to be HIP66725 of magnitude 6.21.  To check my estimate, M3's "official" magnitude is 7.0 (all magnitudes and other info from Starry Night Pro 5.8.2).  In binoculars, I find it easily as one star on a nearly-isoceles triangle a little longer but narrower than a full moon.  The two stars are HIP66725 (mag. 6.21) and HIP67028 (mag. 7.09). M3 appeared to be a white fuzzy patch with a noticeably bright center. None of its stars could be resolved. The dimmest star seen in the field is HIP66498, magnitude 8.56 (diamond). Arcturus got a halo around it about 22:10EDT, and stars in the field became harder to see. The mist disappated some in a few minutes. Transparency went from about 4 to about 3 and back to nearly 4.