Lehigh Valley weather: Threat of severe storms with large hail and high winds returns to forecast (UPDATE)

Severe weather outlook July 29, 2021

Severe weather outlook July 29, 2021, includes much of the Lehigh Valley.National Weather Service

UPDATE: Tornado watch issued across Pa. and N.J. as storms approach

With a warm front rising from the south destabilizing the atmosphere and a cold front bringing storms from the northwest, there is a threat for severe weather on Thursday afternoon into the evening, forecasts show.

The region at greatest risk was moved north on Thursday morning to include the much of the Lehigh Valley and a piece of Warren County and then down toward Philadelphia, the Storm Prediction Center said.

EPAWA Weather Consulting meteorologist Bobby Martrich tweeted just after 9 a.m. that he didn’t agree with the move.

“I’m telling you there’s going to be a day where the SPC agrees with me,” he wrote. “Today is not that day. Instead (they) are expanding the enhanced risk farther to the NE. Don’t think I can endorse this.”

Martrich earlier said the northern boundary of the risk area should be closer to Philadelphia.

An area that reaches from the Valley down into Maryland is labeled an enhanced risk for severe weather, the Storm Prediction Center said. Enhanced is the third level of the five-unit scale. The rest of the region -- including northern Northampton County -- is at a slight risk, which is second on the scale, with level five being high risk.

The National Weather Service in its Lehigh Valley forecast said “some storms could be severe, with large hail, damaging winds, and heavy rain”. The Mount Holly, New Jersey, office’s forecast discussion also spoke of a tornado risk.

Martrich said the same line of storms brought 80 mph winds and tennis ball sized hail to Wisconsin.

But with cloudy skies dominating in eastern Pennsylvania -- there likely will be rain in the morning -- the risk of severe weather in the Lehigh Valley could be lessened, Martrich said in his morning forecast video. He sees the greater risk closer to Philadelphia and into South Jersey as the line moves northwest to southeast. The line could feature supercell thunderstorms and the possibility of tornadoes, he added.

If early Thursday were mostly sunny, it would be a different story in the Valley, he said. The clouds could “keep a lid on severe weather ... preventing all hell from breaking out,” which would be a more likely scenario if the sun were out to heat things up, he said. The high temperature isn’t expected to break 80, the weather service said.

But the situation remains “fluid”, Martrich said, so people should keep an eye out for watches and warnings as the day moves along.

At the moment, the weather service only has a hazardous weather outlook, which cautions about the potential of flooding. Up to an inch of rain could fall, the weather service said, but that could change depending on where the storms pop up.

And, once we get through all this, a couple of beautiful summer days are on the agenda, forecasts show.

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Tony Rhodin can be reached at arhodin@lehighvalleylive.com.