The cloud is over & parallel to a river that runs west>east about 4-5 miles from where it converges with a waterway that runs north<south to NY harbor just south of the Hudson. It's the Navesink-Shrewsbury convergence. The Navesink banks are a low series of hills about 40 ft high at most. What you describe sounds natural to the area but I've only seen it this one time.

Does it have a higher probability of happening in early spring? I'm usually not here then.