BETHLEHEM, Pa. — With a roadmap toward spooky season, the Lehigh Valley’s weather looks to match the fall decor now blanketing stores across the region.
After a brief return to the heat and humidity on Monday — with highs in the upper 80s and low 90s expected — a cold front moving north to south will eject that heat in short order, forecasters say.
- The Lehigh Valley will see temperatures in the upper 80s and a heat index near 90 on Monday
- But a cold front will quickly eject the heat from our area
- Afterward, Canadian high pressure is likely to have a big influence on our weather
“It’s going to kick that ridge [heat dome] out and send it back and retrograde it back to the southwest, and we’re going to have a lot cooler temperatures tomorrow,” EPAWA meteorologist Bobby Martrich said in his latest video forecast.
EPAWA's 8/21 and week ahead outlook, covering:
— Bobby Martrich | EPAWA (@epawawx) August 21, 2023
■ Hotter temps today with ridging over the region
■ Dry cold front keeps it cooler Tuesday onward
■ Precipitation holds off until the end of the weekhttps://t.co/kCCmgIdqsT
And it won’t just be for a day or two.
The government’s Climate Prediction Center suggests temperatures below average through the end of the month and beyond.
A different kind of Canadian influence
Throughout the spring and summer, wildfire smoke has spilled from Canada into the United States and made air quality hazardous for millions.
Monday could even see more of that vertically integrated smoke high in the atmosphere across the Mid-Atlantic region, especially south of our area.
But soon, we’ll see a different kind of Canadian influence on our weather.
A Canadian high — or a North American high — is a large, weak semi-permanent atmospheric high-pressure center produced by the low temperatures over northern Canada.
"A little unorthodox for this point in August."EPAWA meteorologist Bobby Martrich, describing the upcoming pattern of cooler temperatures
In summer, the Canadian high usually is intermittent and occasionally provides cool, dry air into the central and eastern United States.
It’s what we can expect later this week.
“Winds are going to shift to the north and you’ll know," Martrich said of Monday’s frontal passage. "You’ll feel the refreshing air coming in.”
But describing the temperatures later in the week — after yet another cold front moves through — he said the air would be “even cooler” with temperatures in the mid 70s for highs by Sunday.
“A little unorthodox for this point of August,” he said. “You still expect to be very much in the heat and humidity … [but] it’s going to be generally cooler and pleasant temperatures.”
Tropical interests could change things
While the cooler pattern looks locked in, there’s a lot going on outside of the region that could influence our weather in the coming weeks.
The National Weather Service said there’s better agreement from deterministic guidance that Canadian high pressure will build southward from Ontario.
“With that said, would not bet the farm on the model consensus holding this far out, especially given any potential curve balls that could possibly result from any number of tropical interests in the Atlantic,” the NWS forecast discussion said early Monday.
“[But] the Canadian high pressure looks rather strong for this time of year, with most areas likely staying below 80 whether it rains or not.”
The National Hurricane Center is monitoring at least five disturbances, including one in the western Gulf of Mexico and three named tropical storms — Emily, Gert and Franklin.
A fifth disturbance located in the eastern tropical Atlantic also has a decent shot at cyclone formation, the NHC said early Monday.
