Originally Posted by zturncutter
I wonder if it's because of your elevation of 18 feet while for instance North Cranberry to the north of you is @ 43 feet. I have noticed that your low temps are similar to mine even though I am further inland. My elevation here is 44 ft.
Lower areas are more prone to having colder air settling in. But ground moisture and surrounding bodies of water will help keep an area from freezing. Example is water front canal property in my area that generally doesn't freeze. One of the Methods I used when I had my Nursery was to water heavy before an expected freeze. Water holds heat longer than air. As the air gets colder it sucks the Heat out of water and stays just a hair warmer. In a light frost, running overhead irrigation help keep ornamental plants from Freezing. As the weather gets colder the irrigation water freezes and burns the Plant with soft leaves. Hard leave plants are more resistant to freezing, but the hard leaf soft leaf is not always universal with Freezing. Some plants are more cold hardy than others.