Looks like my ol' pal Dot-tailed Whiteface (Leucorrhinia intacta).

Thank you! I've been using an online digital library of maine dragonflies as my research guide, but the picture there only showed one yellow spot, not the several like in my photo. I double checked my other pictures, which included a side shot, and there is indeed a white face which I didn't notice before. Now that I've searched other pictures of this skimmer, I've found several others showing the line of yellow spots. Is there a regional explaination for the variation? Is it more likely that this is a female? Thanks for your help again!

Yes, the males eventually turn all black with just the one yellow dot.