Effects of the Underlying Surface
Cold fronts are often depicted on surface analyses as straight lines but this is not necessarily true. The surface front is actually a three-dimensional structure that is affected by numerous physical processes. Among them are frictional effects due to differences in the underlying surface that can slow or increase the speed of the front on local spatial scales. This means that the front could be depicted as a line straight when passing over uniform terrain with uniform ground cover. Over varying terrain or varying ground cover the front will meander to some degree. The current data-sparse surface network in many areas does not lend itself to identifying such non-linear paths, but Doppler radar has the resolution to do it.
In the image above, note how the cold front does not form a straight line, but seems to surge in some places while holding back in others.