BETHLEHEM, Pa. — A significant warmup is set to take hold across the Lehigh Valley this weekend and intensify into next week, bringing the region its first sustained stretch of summerlike heat of the season, according to the National Weather Service.
Forecasters say Friday will mark the last notably cool day for the foreseeable future, with highs in the mid-60s to near 70 degrees under a mix of clouds and sunshine.
Conditions will turn warmer Saturday and Sunday as a strong upper-level ridge builds across the eastern United States, supported by high pressure offshore and a developing southwesterly flow, the weather service said.
High temperatures are expected to reach the upper 70s to low 80s Saturday, followed by mid to upper 80s Sunday inland.
A stray shower or thunderstorm cannot be ruled out late in the weekend, but most of the period is expected to remain dry, forecasters said.
Turning up the heat
By Monday, the heat is expected to intensify further, with widespread upper 80s and pockets of low 90s possible across eastern Pennsylvania.
The hottest stretch is expected Tuesday into Wednesday, when some inland areas could reach the mid-90s and the region may flirt with record high temperatures.
However, forecasters caution that the setup does not strongly support both extreme heat and oppressive humidity developing at the same time.
In its forecast discussion, the weather service noted:
“In terms of overall heat impacts, the current forecast has the urban corridor flirting with heat advisory criteria by next Tuesday into Wednesday, but that said, this particular setup doesn’t look exceptionally favorable for both very high heat and humidity.
"Through Tuesday, mixing should keep dewpoints from getting too high. Evapotranspiration will be limited due to ongoing drought and ocean temperatures remain cool.
"Long story short, it is still quite early in the season for high dewpoints to combine with high heat. By the time these numbers creep up by Wednesday, clouds and showers/storms may help knock temperatures down some.”
'Like a flip of a switch'
Even so, heat impacts may still be significant due to the duration and intensity of the warm spell, especially in urbanized areas where temperatures will hold in the upper 80s to mid-90s for multiple days.
AccuWeather forecasters emphasize the sharp nature of the transition from recent cool conditions:
“It will feel like a flip of a switch across the Northeast starting this weekend, with temperatures jumping from springlike levels to midsummer territory.
After a chilly stretch, this will be a noticeable change, especially with temperatures running 5 to 10 degrees below the historical average across parts of the interior Northeast and Midwest so far this month.”
While the weather service suggests humidity may be somewhat limited early in the warmup, AccuWeather notes that moisture will still increase as the heat builds, straining air conditioning systems during the hottest afternoons.
“Millions of air conditioners will be turning back on, with temperatures expected to push above 90 degrees in parts of the mid-Atlantic early next week,” AccuWeather said.
“RealFeel Temperatures could approach 100 degrees for a few hours in some locations due to the combination of heat and sunshine.”
A cold front is expected to arrive late Wednesday, bringing the potential for showers and storms and finally easing temperatures back toward seasonal norms heading into late next week.
