It seems to me that you are feeding ListContourPlot a simple matrix of speed values. This way the frame labels will only note the position within the matrix. To get more meaningful frame labels you should give a list (not a matrix) of triples {pressure, latitude, speed} or whatever. Compare the labels:

ListContourPlot[Table[Sin[i + j^2], {i, -1, 2, 0.1},
  {j, 0, 3, 0.1}]]
ListContourPlot[Flatten[Table[{j, i, Sin[i + j^2]},
   {i, -1, 2, 0.1}, {j, 0, 3, 0.1}], 1]]

As for adding lines on top of the contour plot, I would recommend Epilog:

ListContourPlot[Table[Sin[i + j^2], {i, 0, 3, 0.1}, {j, 0, 3, 0.1}],
 Epilog -> {Line[{{-20, -20}, {20, 20}}]}]

It appears to be a problem of PlotRange. When you Show more than one plot, the overlay will use the PlotRange of the first plot. Also, if gLEV2 is last, it will sit on top of the previous lines and make them invisible underneath. Place gLEV2 first in the list:

Show[gLEV2,lineLONGRA, lineTRKGRA, lineTURGRA]

Otherwise, use Epilog within ListContourPlot. By the way, there is no need for Show when only one Graphics is inside: Show[Graphics[lineLONCUR]] is the same as Graphics[lineLONCUR]