Weather/physics question

Weather/physics question

To all you smart people on this list I have a question: I live in northern Virginia, outside of Washington, DC. Last night the temps in my neighborhood dipped to 38 degrees F (I have an outdoor digital thermometer, that is very acturate). I noticed that some roofs and lawns had actual frost on them this morning. How can there be frost if the temp was 6 degrees F, above the freezing point? Respectfully, Flummoxed in Falls Church
Sweet Southern Comfort :)

Sweet Southern Comfort :)

The back garden again.

The back garden again.

Pics of my garden!!

Pics of my garden!!

my wall of rosemary

my wall of rosemary

My jumbled garden

My jumbled garden

Today’s harvest

Today’s harvest