WRF Version 3.3.1 was released on September 22, 2011.

WRF Version 3.3.1

Bug Fix for Morrison Microphysics Option (posted 11/16/11)

Problem: A bug was introduced in V3.3.1 in Morrison microphysics scheme. The bug affects cloud ice fallspeed, and hence cirrus lifetime and radiative forcing. The effect of the bug is less in shorter simulations, but significant in terms of high cloud cover and LW radiative forcing in longer-term climate runs. This bug is not present in V3.3 and earlier.

Solution: Edit phys/module_mp_morr_two_moment.F, and change line 1289 to

AIN(K) = (RHOSU/RHO(K))**0.35*AI

or download the routine.