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
My room today

My room today

So this is my room

So this is my room

Spring in my yard in Western PA

Spring in my yard in Western PA

my pumpkin patch

my pumpkin patch

Sharing some signs of spring

Sharing some signs of spring

Mystery plant

Mystery plant