A plume of moisture is on the way for the Lehigh Valley. Here’s when the heaviest rain could fall.

BETHLEHEM, Pa. – An active weather pattern will ramp up Friday and continue in the Lehigh Valley through the weekend and beyond as a plume of moisture surges into the area, forecasters warn.

There is a marginal risk of excessive rainfall across the region Friday into Saturday as heavier rains over the Ohio and Tennessee Valleys lift northeast, according to the Weather Prediction Center.

• Tropical moisture from the Gulf is being pumped northwestward into the region
• The heaviest rainfall is expected late Friday afternoon through Friday night
• There could be some clearing Saturday afternoon before rain returns Sunday

“It will be able to take advantage of the warm frontal/tropical moisture from the Gulf being pumped northwestward into the Mid-Atlantic,” the WPC’s forecast discussion notes, with expected rainfall totals continuing to increase for the Friday afternoon time frame.
Here’s how the next few days could play out:

Friday

Light to moderate rain eventually will be widespread across the region Friday, but forecasters say instability will contribute to locally heavier rainfall.

“Soils are very dry over the area, but the long-duration rain with heavier rain embedded will likely result in isolated flash flooding, especially in urbanized and poor drainage areas," according to the forecast. "The feed of moisture will be slow to diminish and move northeast.”

NOAA

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Weather Prediction Center

According to the National Weather Service, the progression of rain will increase throughout the morning from south to north. The heaviest rain in the Lehigh Valley looks to occur late Friday afternoon through Friday night, based on the available short-range guidance.

Winds also are expected to ramp up Friday into Friday night, with sustained winds of 15 to 25 mph expected and gusts up to 30 to 35 mph possible Friday night into Saturday morning.

Saturday

Showers and periods of rain “are going to go overnight and into Saturday morning,” EPAWA meteorologist Bobby Martrich said in his latest video forecast.

“I do think there’s an opportunity for some drier conditions here in the afternoon,” Martrich said, with models generally agreeing on the potential for that system to clear out and pull away perhaps after 2 or 3 p.m. in the Lehigh Valley.

“The timing is such that it’s not going to be an all-day washout,” he said.

In terms of rainfall totals, the weather service said we’re looking at a widespread 1-1.5 inches of rainfall through Saturday, “which would be much-needed rainfall considering most of the area has been abnormally dry.”

Sunday

“We are expecting it to be clear overnight Saturday [into Sunday], or at least dry,” Martrich said, but rain will return to the area for much of the day Sunday.

“This system has sped up a bit … and you have an increase in rain chances,” he said. “Showers during the course of the day and then once we get into the evening and overnight there could be some heavier rain involved with this as low pressure moves directly over the region.

“It looks like Sunday is not going to be a good time,” Martrich said.

According to the weather service, the general idea for the long-term is for the unsettled weather pattern to continue through the early portion of next week.