Philadelphia fire: Smoke from Frankford building fire covers part of Philadelphia skyline

Commuters heading into Philadelphia on Friday morning noticed part of the city's skyline covered by smoke from a massive building fire.

Over 100 firefighters battled a massive fire that sparked inside a multi-story building in the city's Frankford section early Friday morning.

The fire, which is still not under control, reached 4-alarms and sent dense black smoke billowing into the air and across the city. 

FOX 29's Kathy Orr explains that the smoke is being trapped closer to the ground by a weather phenomenon known as a "temperature inversion."

A temperature inversion, Orr explained, is when cold air is trapped in the lower levels of the atmosphere and warmer air rises above.

The smoke plum from the massive fire was substantial enough to briefly pop up on FOX 29 Weather Authority's radar.

The smoke could not only be seen in Philadelphia and surrounding areas, but could also be smelled across the river in Camden.