  We present optical observations and 2D hydrodynamic modeling of an isolated
shocked ISM cloud. H$\alpha$ images taken in 1992.6 and 2003.7 of a small
optical emission cloud along the southwestern limb of the Cygnus Loop were used
to measure positional displacements of $\sim$ $0 \farcs 1$ yr$^{-1}$ for
surrounding Balmer dominated emission filaments and $0\farcs025 - \farcs055$
yr$^{-1}$ for internal cloud emission features. These measurements imply
transverse velocities of $\simeq$ 250 km s$^{-1}$ and $\simeq$ 80 -- 140 km
s$^{-1}$ for ambient ISM and internal cloud shocks respectively. The complex
shock structure visible within the cloud indicates that the cloud's internal
density distribution is two phased: a smoothly varying background density which
is populated by higher density clumps. We present model results for a shock
interacting with a non-uniform ISM cloud. We find that this cloud can be well
modeled by a smoothly varying power law core surrounded by a low density
envelope with a Lorentzian profile. The lack of sharp density gradients in such
a model inhibits the growth of Kelvin-Helmholtz instabilities, consistent with
the cloud's appearance. Our model results also suggest that cloud clumps have
densities $\sim$ 10 times the ambient ISM density and account for $\sim$ 30% of
the total cloud volume. Moreover, the observed spacing of internal cloud shocks
and model simulations indicate that the distance between clumps is $\sim$ 4
clump radii.
