Conditions right tonight for frequency skipping in the NE US

This evening I flew from Buffalo, NY, down to Cleveland, over to
Binghamton, NY, and back home to Syracuse for an Angel Flight. Total time
in the air was probably 3 hours just before sunset.

At first I thought something was wrong with my Garmin GNS430 radio because
I kept hearing numerous pilot-side communications, but no ATC. This
happened on the Buffalo departure frequency, the Erie, PA, approach, and
the Cleveland approach frequencies.

Just after departing Cleveland, I heard this again, but this time I caught
a check-in. The pilot mentioned Chicago Center and it finally became clear
to me that I was hearing pilots from 600 to 1,000 miles away.

Is this phenomenon called skipping? What causes such a large outbreak of
this, high clouds or something else? A very interesting evening, as it was
occurring on just about all of the center and approach frequencies that I
was monitoring.


--
Peter