It happens only once, an explosion of pollen every spring.

This explosion we're talking about is the explosion of pollen when decks and cars become covered in a greenish yellow.

"It'll happen sometime around early April through May, the 3-4 weeks when we have, pretty much everything blooms at the same time," James Long, an instrument technician with the Air Pollution Control Bureau in Chattanooga, said.

During winter, everything is dormant, which means the initial burst of pollen is right around the corner.

Pollen counts are observed first thing in the morning at the bureau. An instrument called a Rotary Rod sampler turns on every 10 minutes and spins for a minute.

Steven Langston, an instrument technician at Air Pollution Control, said, "this collects pollen on it. There is some grease we put on there, so when it spins, it collects the pollen."

Langston takes observations every morning at 8:00 am. He then carefully adds the counts under a microscope. He says the pollen explosion should happen in the next week or two. In his 20 years of experience, he says he's noticed trends like lower pollen counts 24 hours prior to rainfall.

"When the explosion happens, it's usually a couple of days before it rains, and it's as if the trees know if it's going to rain or not, and when is the premium time to release pollen," adds Langston.

A few things could be happening here. Humidity levels tend to be higher with approaching low-pressure systems. Unless there is a dry, warm day, pollen may not be released because it would be a waste, especially on a day with no wind.

Cathy Jones, Air Control Monitor says don't fret, though, if you start to see pollen in the next week or two.

"If you see a lot of pollen on your driveway, it may be pollen it's so big it's not respiratory," says Jones.

She adds respiratory issues occur from the microscopic pollen that we're seeing now, such as pine.

Counts look lower on Thursday when it will rain, while sunshine and a drier weekend should bring pollen counts back up for Easter Egg hunts this weekend.

Have a weather-related story idea? Feel free to email Meteorologist Brittany Beggs.