The atmosphere might be primed for another spell of mayhem Thursday in the Philly region, forecasters are warning, with a potential for strong storms — this time more widespread — and an outside chance of a tornado.
It is even possible that the region might see the official debut of the National Weather Service’s new “destructive” designation, freshly added to its storm warning lexicon.
“I can’t rule it out” said Michael Silva, a meteorologist with the weather service office in Mount Holly. ”We’re expecting a fairly strong outbreak in the afternoon.”
Said Bob Smerbeck, senior meteorologist at AccuWeather Inc.: “The potential is there.” He added that in this case, damaging storms could be widespread, as opposed to the more highly localized outbreaks of recent weeks.
The government’s Storm Prediction Center has the entire region under an “enhanced risk” of severe storms, the primary threat being wind gusts approaching 60 mph, with a slight chance of a tornado.
The forecasts, however, come with more than the usual assortment of caveats, meteorologists cautioned. The wild cards include that stubborn atmospheric smoke.
The air-fouling smoke has resisted various thunderstorm rinse cycles and continues to layer a milky film, and at times sun-obscuring clouds, across the skies. The National Centers for Environmental Protection are forecasting another smoky invasion Thursday.
As the wildfires have persisted in the Pacific Northwest, so have the upper-level jet stream winds that have been exporting it toward the Atlantic Coast. “This summer the weather patterns just seem so stagnant,” said William Gallus, an atmospheric scientist at Iowa State University who in recent weeks has seen more smoke than he would have cared to.
By shaving a few degrees off the temperatures, the smoke might subtly reduce the surface heating that launches warm air high into the atmosphere and detonates thunderstorms. However, he adds, solar heating isn’t the only storm-triggering mechanism.
Smerbeck suggested that the smoke is about to meet its match locally. Philadelphia will remain tantalizingly close to a warm front while a storm approaches from the northwest with an attendant cold front, he said.
The contrasting air masses are likely to blow up storms that would be intensified if the sun manages to break through during the day, he said, the smoke notwithstanding.
“The air is going to be very, very juicy,” he said, and might be ripe to spawn “supercell” thunderstorms, and possibly a tornado.
After the front sweeps through, the aftermath will be a taste of September. Saturday’s highs in the low 80s would be normal for a Sept. 8.
In addition to a refreshing air mass, the region also should see quite a refreshing change overhead — a deep blue, smokeless sky.
“I think you’re going to see it this weekend,” said Smerbeck.