Forecasters: Heavy rain, cooler air on the way

Residents of the Lehigh Valley who enjoyed a brief return to warmer temperatures will see the calendar and the season flip to fall later this week.

An October-like air mass will sweep through the region, bringing heavy rain and rumbles of thunder, meteorologists say. Flash flooding is possible late Tuesday into Wednesday.

Following another day or two of cloudy and muggy weather, the focus will turn to a slow-moving cold front expected between Tuesday night into early Thursday.

According to Empire Weather, which provides localized forecasts for The Morning Call, most moisture will remain to our west on Tuesday. There likely will be a few showers during the day, perhaps with a rumble of thunder, before the system becomes more organized.

On Tuesday night, it ’s possible the Valley will see the front slow, and possibly even stall over the the region. This could lead to several inches of rain with localized flash flooding.

Beyond that, the forecast gets tricky. Empire Weather says one scenario would have a lull in precipitation, and then a second wave of heavy rain on Wednesday night. Another scenario is more progressive, with all rain being out of the area earlier Wednesday as the region starts to dry out.

By the end of the week, heating demands will start to ramp up as a second cold front crosses the region.

According to the National Weather Service, temperatures could be 5 to 10 degrees below normal by Friday. Daytime highs will be in the low 60s, with overnight lows in the 40s.

The amplified jet stream pattern is expected to bring intense heat to the west and chilly air to the east as October kick offs. High temperatures next week will not exceed the mid to low 60s.

The Climate Prediction Center puts the Lehigh Valley at a 60% to 70% chance of below average temperatures through Oct. 7.