A 'tremendous amount of rain' inundates the Lehigh Valley, with a parting shot expected Monday

BETHLEHEM, Pa. — Swaths of the Lehigh Valley were inundated by heavy rainfall on Sunday, leading to flash floods and prompting water rescues.

The rainfall neared 5 inches in parts of the area, including Tatamyin Northampton County, which saw 4.91 inches.

A flash-flood warning was declared by the National Weather Service for the Allentown, Bethlehem and Easton areas through 11:30 p.m. Sunday.

The NWS reported 2.35 inches of rain at Lehigh Valley International Airport, while nearby stations on the Ambient Weather Network, including one off Bridle Path Road in Bethlehem, reported 3.50 inches.

The northern tip of Palmer Township had 4.31 inches, one observer reported.

Nazareth also was hard hit, with the intersection of South Broad Street and Jancy Boulevard closed by flooding, with water rescues reported.

How it happened

EPAWA meteorologist Bobby Martrich said Sunday’s heavy rain was caused by a “convergence boundary” that set up in the area.

“If you were along that boundary or just north of it, you got smoked yesterday,” he said in his latest video update, highlighting areas closest to the Interstate 78 corridor.

A convergence boundary, or convergence line, is a band of clouds that remains fairly stationary and can produce large amounts of rain across a relatively small area.

“There was a pretty nasty line that just sat here and sat here and sat here,” he said.

But nothing compared with what happened in parts of Connecticut, which experienced a “1,000-year” rain event, meteorologists said, or an event that has just a 0.1% probability of occurring in any given year.

Data from the weather service late Sunday showed nearly 10 inches of rain in the town of Monroe in Fairfield County, with Middlebury in New Haven County getting 9.55 inches.

A ‘parting shot’ on Monday

A secondary cold front moving toward the region will bring a parting shot Monday afternoon and evening, forecasters say.

The front will help to instigate another round of showers and storms, but should be moving along much faster than they did on Sunday.

“We had the cold front yesterday that brought the scattered showers and thunderstorms and a tremendous amount of rain in some areas, and other areas are like, ‘What rain?’” Martrich said.

“The flood watches that were up from the National Weather Service for 3 to 4 inches wasn’t great for everywhere, but for the areas that got hit hard, it certainly verified."

Isolated severe storms will be possible again Monday, with damaging winds the main threat.

“It will be ushering in the cooler air for the next couple of days, and some very pleasant conditions are coming in,” Martrich said.