golfyankeesierra -
The radarsignals are reflected by the heavy precipitation in the cells, back to the radar so they never reach the area behind the cells. That means that you'll never exactly know what is behind the first storm untill you passed it.
I don't know what 'bands' are being used these days, but your statement implies "X" Band Radar. Why airliners were ever fitted with 'X' Band, I'll never know. With "C" Band that we had, you could 'see' through cells with no problem.