Severe storms are possible in the Philly region Wednesday during the late-day commute
A "squall line" will move through the region, and an isolated tornado "can't be completely ruled out," says a National Weather Service meteorologist.
In what might be viewed as the advancing spring’s “warning shot” to the remnants of winter, strong thunderstorms are possible late Wednesday afternoon and evening in the Philly region, with an outside chance of an isolated tornado.
The government’s Storm Prediction Center has part of the region under a 40% risk of severe storms — defined as those with winds approaching 60 mph — in what has been quite a gusty period.
As for the tornado possibility, while the potential would be greater south of Philadelphia, “it can’t be completely ruled out anywhere,” said Sarah Johnson, the warning coordination meteorologist at the National Weather Service Office in Mount Holly.
What time would the most severe weather occur in Philadelphia?
Some rain is possible earlier in the afternoon with the approach of another cold front, but any stronger storms likely would arrive between 4 p.m. and 8 p.m. in the city, said Dave Dombek senior meteorologist with AccuWeather Inc.
He said wind gusts to 50 mph are possible, downpours could cause some road ponding, and hail isn’t out of the question.
SEPTA advised it would put crews in place to clear tracks should any power lines or trees come down along Regional Rail or trolley lines.
Regional Rail ridership is up about 15%, or about 10,000 commuters during this Flower Show week, said SEPTA spokesperson Andrew Busch. Some of them may not be well-acquainted with the disruptive potential and heavy rain and winds, he added.
In terms of preparation, “We’re throwing as much as we can in terms of staffing,” he said.
He added that ironically, that may bode well for the weather: “The stuff you prepare best for doesn’t happen.”
What’s behind all the gusts in the Philly region in the last few months?
This would be another in a sequence of fronts that form at the boundaries of warm and cold air and air of different pressure, or weight.
The nine days in January and February that featured 40-mph or greater gusts were the most of any January-February combination of the last five years. That had do with frequent presence of high pressure, or heavier air, to the west, and lower pressures to the east, according to Jon Gottschalck, a chief forecaster at NOAA’s Climate Prediction Center. Heavier air naturally moves toward lighter air.
March began Saturday with yet another wind fest, with surprisingly strong gusts to 50 mph.
Statistically, March is the windiest month of the year in Philadelphia as the ambitious spring advances against the waning winter. The upper air retains the chill — it has often snowed with temperatures above freezing this time of year — while the sun’s increasing power is heating the ground. That creates instability and storminess as warm air rises over colder air.
From spring’s perspective, severe weather is “kind of a warning shot” to winter to go back where it came from, said Dombek.
While “you don’t want to close the book” on winter, he added, and late snows are known to happen, its days are numbered.
The storm threat does have an upside for the Philly region
No snow is anywhere in the outlooks, but the region should get a decent rain, perhaps as much as an inch, Dombek said.
Precipitation the last 60 days has been about 50% of normal throughout the region, and drought advisories remain in effect, along with a noticeable puddle shortage.
The climate center’s March 12-18 outlook suggests a possible reversal of the trend, favoring above-normal precipitation.