I was in Kearney the first week in March this year for some work. I had
time to do some crane viewing before and at sunrise, and another time near
and at sunset. I was early for the migration and there were still tens of
thousands of cranes and snow geese. A good place for viewing is Alda
Road South, about 8 miles east of Kearney. During the day the cranes are
all over the fields everywhere and flying around, but at sunrise and sunset
there is a mass flight which is spectacular. There is a lot of local
information about where to go. Also, the day I arrived it was almost
80deg, and two days later in the morning it was 6deg.

Here are a few pictures: https://flic.kr/s/aHBqjBfZcS

I flew in and out of Omaha, which is a three hour drive to Kearney. It
was more reliable than flying into Kearney and trying to rent a car.
Alaska Air has a nonstop flight from Seattle to Omaha.

Hope this helps - Jay