Forecasters: You'll feel a big difference as fall weather starts to settle in

• Heat and humidity are exiting the region, just in time for fall
• The autumn equinox officially arrives Saturday, Sept. 23
• The long-range outlook calls for a stretch of dry weather and seasonal temps

BETHLEHEM, Pa. – Just days away from the official start of fall, forecasters say the Lehigh Valley will see a long stretch of dry weather and seasonal temperatures ahead.

It comes after temperatures ran 4.1 degrees above average the first 12 days of the month, including a four-day stretch in the 90s from Sept. 4-7.

Now, fall-like weather is on the horizon, with mostly sunny skies and highs generally in the 70s, which is several degrees below normal for this time of year.

More importantly, forecasters say surface dew points will generally be in the 50s as we finally lose that warm and muggy air mass that had been draped over the region.

When is the first day of fall?

There are officially less than 10 days left of summer, with the autumn equinox arriving at 2:49 a.m. on Saturday, Sept. 23.

The date varies slightly year to year, but is usually Sept. 22 or 23. On rare occasions, it can also fall on Sept. 21 or 24. It not only marks the period where the growing season begins to end, but temperatures drop and days become shorter than the nights.

The Lehigh Valley will lose about 2 minutes and 39 seconds of daylight on average through the remainder of the month following the equinox. By Sept. 30, sunrise will take place close to 7 a.m., while sunset will be at 6:45 p.m.

Overnight lows fall off

“We have a big trough settling into the region and cooler temperatures coming into the region,” EPAWA meteorologist Bobby Martrich said in his latest video forecast.

Martrich flagged the lower humidity as “something everybody likes” and noted a string of days with highs in the low to mid 70s ahead.

Overnight lows will also fall off into the low to mid 50s across the Lehigh Valley.

Last September, the area saw its first overnight lows in the 40s on Sept. 16, then temperatures pushed back above average until the first day of fall arrived.

A perfect leaf-peeping forecast?

The timing of this year’s peak fall foliage could depend on how the rest of this month shakes out, temperature-wise, LehighValleyNews.com’s Molly Bilinski reported this week.

“If we have an abnormally warm September, then it’s going to be delayed,” said Ryan Reed, a program specialist with the Pennsylvania Department of Conservation and National Resources. “If it cools down really nicely — as you might expect, through history — then, you should expect it to be a pretty normal season in terms of timing.

“It’s a little too soon to tell, but I would say that’s a good baseline,” Reed added.

The Valley generally peaks in mid-to-late October, but the weather over the next few weeks could give clues to further narrow down timing.