  Our main observations are: (i) The effective path length of the $c\bar c$
wave packet, which is produced in the nucleus, grows with the energy of the
produced charmonium. The variation is controlled by the coherence length
$l_c=2E_{\Psi}/M^2_{\Psi}$. (ii) A colorless $c\bar c$ wave packet produced in
$pp$-interaction is a specific linear combination of the $J/\Psi$ and $\Psi'$
states, and interacts substantially weaker that any of its components. The time
evolution of this wave packet is controlled by the formation length,
$l_f=2E_{\Psi}/(M^2_{\Psi'} - M^2_{\Psi})$. Exact formulas incorporating with
these effects are derived. The interplay of the two phenomena results in a
nontrivial energy- and $x_F$-dependence of the nuclear suppression of the
charmonium production in proton-nucleus and nucleus-nucleus collisions and
explains some of the experimentally observed effects.
