A flood watch is in effect until 2 a.m. Tuesday for Lehigh and Northampton counties, according to the National Weather Service.
Scattered and potentially strong thunderstorms could drop an inch of rain as a warm front moves through the Lehigh Valley. The flood threat is heightened because local streams and rivers are already high.
A chance of rain will continue Tuesday with a forecast of cloudy skies and a high of 82.
Showers and storms are also possible Wednesday and Thursday.