  With Hubble Space Telescope Wide-Field Planetary Camera 2 observations of the
Cygnus Loop supernova remnant, we examine the interaction of an interstellar
cloud with the blast wave on physical scales of 10^15 cm. The shock front is
distorted, revealing both edge-on and face-on views of filaments and diffuse
emission, similar to those observed on larger scales at lower resolution. We
identify individual shocks in the cloud of density n~15 cm^-3 having velocity
v_s~170 km/s. We also find the morphologically unusual diffuse Balmer-dominated
emission of faster shocks in a lower-density region. The obstacle diffracts
these shocks, so they propagate at oblique angles with respect to the primary
blast wave. The intricate network of diffuse and filamentary H alpha emission
arises during the early stage of interaction between the cloud and blast wave,
demonstrating that complex shock propagation and emission morphology occur
before the onset of instabilities that destroy clouds completely.
