Digital BW, The Print

I have recently started printing with the UT2 inkset and for the most 
part I'm very happy with the results. I made a printer profile with 
Pantone ColorVision scanner and it seems to work pretty well. I have an 
image of lightning that I shot with my modified infrared camera that I 
would like to print black and white. When I try to print the image it 
comes out with narrow bands radiating from the lightning to the dark 
sky. On the screen its a nice smooth transition, but on the paper its 
very noticable transitions. When I print it with color inks it comes 
out smooth like on the screen. Any suggestions would be greatly 
appreciated.
Brian