If you have houseplants or tender vegetation outside you may want to cover it or bring them inside tonight, as patchy frost is possible after midnight tonight.
The National Weather Service has issued a frost advisory for the area from 4 to 9 a.m. Tuesday, when temperatures are forecast to drop into the low to mid 30s.
The forecast low for Allentown is 35 degrees.
It has been a relatively mild fall so far, and this would be the first frost of the season.
A frost advisory means a fairly widespread frost is expected. Sensitive outdoor plants may be killed if left uncovered.