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Environment & Science

Lehigh Valley weather pattern will be sunny and pleasant before an onslaught of heat

Weather pattern
This graphic shows expected high temperatures on June 10 and expected high temperatures on June 19.

BETHLEHEM, Pa. — "If you’re not a fan of the heat and humidity in summer, I have a couple days this week that are going to be your days,” EPAWA meteorologist Bobby Martrich said in his Monday video forecast.

But Martrich cautioned that Mother Nature would flip the script in a big way later in the week.

“We do have some other days this week that are not going to be your days,” Martrich said, offering insight of what’s ahead — with hints of the region’s first heat wave in the long-range outlook.

Reinforcing cold front kicks things off

After a beautiful weekend, Martrich said a reinforcing cold front will result in cooler conditions hanging around the Lehigh Valley over the next couple of days.

“We’re going to have lower temperatures in the 70s and lower humidity [Monday], and that’s going to be the same case here for Tuesday,” he said.

A mixture of clouds and sun will accompany this reinforcing shot of cooler air, with a loss of daytime heating in the evening resulting in overnight lows in the mid-50s across the area.

But once we get past that, we’ll have temperatures start to rebound on Wednesday, Martrich said.

When to expect ‘peak heating’

Looking ahead, all indications continue to point toward a significant warmup by the end of the week and beyond as ridging starts to build into the region.

A ridge is defined as an elongated area of relatively high atmospheric pressure, and a broad region of sinking air or a deep, warm air mass will both lead to ridging.

And since air often is sinking within a ridge, it tends to bring warm and dry weather.

That’s what we can expect by the end of the week, Martrich said, with Friday likely to be a day of “peak heating,” when temperatures push into the 90s across most of the area.

“For the areas that have not reached 90 so far this year, you might do that by the time we get to Friday,” he said.

Then we’ll await a cold front punching through that could bring shower and storm activity Friday night that will bring lower humidity and more comfortable conditions.

Heat wave ahead?

8 to 14 day temperature outlook
This is the 8 to 14 day temperature outlook from the Climate Prediction Center. Temperatures are expected to soar in the Mid-Atlantic and Northeast before the official start of summer arrives.

Looking ahead to next week, Martrich said he believes we’ll have “a really hot stretch going for much of the work week.”

The National Weather Service also is indicating a significant warmup that could bring the first heat wave of the year.

The NWS defines a heat wave as a stretch of abnormally hot weather generally lasting more than two days. In the Mid-Atlantic and Northeast, the 90-degree mark is the unofficial threshold for most areas.

“I think we’re getting into a summer pattern very solidly heading into next week and even after that,” Martrich said.

The summer solstice officially arrives Thursday, June 20. Early indications are that temperatures could be in the 90s when the season officially kicks off.