Heavy rain and melting snow prompted the National Weather Service to expand the flood watch's reach.
A flood watch already in place for parts of Pennsylvania and New Jersey has been expanded to cover portions of Northampton and Warren counties, the National Weather Service said Wednesday afternoon.
The watch is in effect through Thursday afternoon for a region encompassing east-central Pennsylvania and northwestern New Jersey. The watch had originally been issued for a region that included Lehigh, Upper Bucks and Hunterdon counties.
Small streams, not rivers, at risk of flooding in Valley
"The combination of melting snow and periods of heavy rain is likely to produce low-lying, poor-drainage flooding later this afternoon and evening," Wednesday's announcement by the weather service states. "Minor to moderate river flooding is likely tonight and Thursday across portions of the Raritan and Passaic basins of north-central New Jersey.
"Road closures are possible later today into Thursday in poor drainage areas and near flood streams, especially in the proximity of the Interstate 78 corridor."
A step below a warning, a flood watch means there is potential for flooding based on the latest forecasts, the weather service says.
In addition to the rain, also exercise caution for patchy dense fog, If you encounter fog, reduce speed & use low beam headlights
-- NWS Mount Holly (@NWS_MountHolly) February 3, 2016
Weather service meteorologists advise continuing to monitor forecasts through Thursday: "If you live in areas prone to flooding, be prepared to take safe, evasive action should flooding develop."
Wednesday's heavy rains are due to a strong low pressure tracking Wednesday afternoon from the Great Lakes into Quebec, the weather service says. A cold front behind the system is forecast to slowly push through the flood-watch region Wednesday night and be off the coast Thursday morning.
"The combination of rain and melting snow will produce flooding in poor-drainage areas," the watch reads. "It's also becoming more likely that flooding will occur along a number of streams and rivers as well."
Beyond the rain, partly sunny skies are forecast Thursday with a high of 47 at Lehigh Valley International Airport. Sun and highs in the low 40s, with nighttime lows below freezing are forecast through Saturday.
Kurt Bresswein may be reached at kbresswein@lehighvalleylive.com. Follow him on Twitter @KurtBresswein. Find lehighvalleylive.com on Facebook.