Use the SGNL parameter stored in the NLDN file to plot
stikes with SGNL < -400 with a '-',
SGNL > 400 with a '+', and values from -400 to
400 with a dot.

Using the result from #3 above, create a gif image for each
hour today. Use a different color for each hour.

You may view the animated GIF
frames output from #5.