Severe thunderstorms are expected later Thursday in Philly. Forget the northern lights, for now.

Some high drama is possible in the skies over Philly tonight, but it won’t be from the northern lights.

The National Weather Service has issued a severe-thunderstorm watch, in effect until 11:59 p.m. Thursday, and a tornado is not out of the question, especially west of the city.

A line of storms, somewhat behind schedule, was advancing eastward and likely would reach the city around 8 p.m., said Sarah Johnson, lead meteorologist at the weather service office in Mount Holly.

Storms arriving later — after sun has done its work of supplying heat energy — are less likely to be severe, she said. Thus the storms would be more likely to focus ferocity to the west, where they would arrive earlier.

The government’s Storm Prediction Center lists a 5% chance of a tornado for Philadelphia, most of eastern Pennsylvania, and areas of New Jersey along the Delaware River. “It’s a possibility,” Johnson said, but the later arrival of the storms would reduce that risk.

In addition, the National Weather Service in Mount Holly says it is possible that conditions might align to incite winds to blow in a corkscrew-like pattern, thus the slight chance of tornadoes, particularly in Chester and Montgomery Counties.

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Meanwhile, a storm watch is in effect for outer space, said Robert Steenburgh, space scientist and acting Lead of the government’s Space Weather Forecast Office, that was the source of the buzz about the potential of seeing the northern lights Thursday night as far south as Philadelphia.

The Space Weather Prediction Center, in Boulder, Colo., reported that a massive solar storm on Monday resulted in a “Coronal Mass Ejection” that was speeding toward earth at about 500 miles a second.

The light display known as the aurora borealis in the Northern Hemisphere is ignited by electrically charged particles from the sun interacting with the earth’s magnetic field, which right now is not aligned favorably for aurora sightings anywhere near Philly, Steenburgh said.

So in this case, the clouds aren’t spoilers: Even the skies were clear, he said, Philadelphia would have “little or no chance” of seeing the aurora.

The undulating curtains of ever-changing light can constitute a surreal, spectacular vision, however they won’t be seen tonight around here.

In addition to the clouds, AccuWeather Inc. astronomy specialist Brian Lada says they likely wouldn’t be visible as far south as the northern Pennsylvania border. However another solar storm and another shot at the aurora is possible on the weekend, AccuWeather says.

Steenburgh said that space center is watching another solar eruption that occurred Wednesday but that is was too soon to know if it would bear auroral fruit.

Lightning is a far-more realistic possibility over Philly Thursday night as the atmosphere is in a state of upheaval.

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Temperatures dropped below freezing on three consecutive days this week, the first time that has happened so late in the season in 40 years in Philly, and it has been exceptionally dry. By contrast, Thursday morning was relatively balmy and the air was swollen with moisture, as evidenced by the heavy dew.

Some showers could break out by early afternoon, however, the nasty stuff is expected to hold off until late in the day or early evening.

This is a developing story and will be updated.