B2 stealth bomber sighting...in michigan?

....we were hanging in lake st. clair yesterday (located a few miles
northeast of detroit and a few miles from selfridge ANG). during the
course of the day there were several overhead passes by F16s and an
occasional C130 approaching the base. then i looked directly above
and saw the unmistakeable shape of a B2 heading due south at perhaps
~5000' AGL and the unfamiliar engine whine was clearly audible.

since this was the first time seeing a B2 in person, not to mention in
flight, this was a pretty cool occurrence as it peeked in and out of
the few sporadic clouds as it headed south. VERY COOL!

so then i'm wondering "what the heck is a B2 doing here in michigan at
such a low altitude?" selfridge doesnt really seem like a staging
location for B2 missions and i have no knowledge of any air shows in
the area.

any ideas as to what a B2 might have been doing in this area?