Winter is finally behind us, which means it's time for spring allergies. From the millions of missed workdays each year, to the booming allergy drug industry, to the spring allergy capital of America—here are a few things you might not have known about allergy season. (Davin Coburn/The Washington Post)

Goodbye, polar vortex. Hello, pollen vortex.

It turns out that this brutally cold, miserably long, snowfest of a winter did more than wreak havoc on the bundled Mid-Atlantic masses. It also caused elms, cedars and other trees that typically flower early in the year to hold off for warmer weather.

Now, with more springlike days finally in the forecast, those trees are poised to pollinate alongside oaks, cottonwoods and pines, as well as some grasses. The result could mean a perfect storm of pollen in coming days — and an especially miserable stretch for allergy sufferers.

“Grab your Kleenex,” said Susan Kosisky, chief microbiologist at the U.S. Army Centralized Allergen Extract Laboratory. “It’s coming.”

Every day on the roof of Kosisky’s lab in Silver Spring, two small greased rods spin through the air, collecting pollen particles. She said that over the past 15 years, the average daily measurement for the first week in April has been about 353 grains per cubic meter of air. That figure can spike to more than 4,000 at the peak of the allergy season.

A delayed wallop of pollen is on the way

Earlier this week, the reading stood at 109 grains per cubic meter, well below average.

That meant temporary good news for many allergy sufferers, Kosisky said. But it also suggested a tidal wave of pent-up pollen could be coming our way as the area heads toward the height of allergy season later this month. In fact, by Friday, the decent weather already had sent pollen counts climbing.

[READ: 10 tips for surviving a severe allergy season]

“As soon as we get four to five days of sunshine in a row, we’re going to see the buds on the trees explode and people are going to be really suffering,” said Clifford Bassett, medical director of Allergy & Asthma Care of New York.

“If it warms quickly, everything is going to pollinate at once,” said Estelle Levetin, a professor of biology at the University of Tulsa who studies airborne allergens.

“Trees, grasses, weeds, even mold spores,” Kosisky said. “In our area, there is something for everyone.”

Soon, the cars and sidewalks that have been covered in snow through much of the winter (and into spring) could be coated in a familiar yellow-green dust. And many people will be trading in winter coats for runny noses, itchy eyes and uncontrollable sneezing.

Abstract oak tree pattern at Gunpowder Falls State Park near Baltimore, Maryland. (iStockphoto)

The danger of a shorter but more intense allergy season, specialists say, is that it could overwhelm immune systems, triggering potentially serious health issues.

“It’s more than just a nuisance for some people,” said Sally Joo Bailey, assistant professor of allergy and immunology at Georgetown University. “On some really bad days, if you have pollen allergies, you could have a severe asthma attack. When your nasal area gets inflamed because of allergies, it doesn’t just stop there. It can get into your lungs.”

Experts say people with allergies can take measures to lessen their contact with pollen, including using central air conditioning rather than opening windows, wearing sunglasses when outdoors and washing their hands frequently. In addition, doctors say patients who know they have spring allergies can begin taking antihistamines before the worst of the season arrives.

This year’s cold-induced pollen delay in the Washington area seems like an anomaly, but it could be part of long-term weather fluctuations affecting allergy seasons everywhere.

Scientists have documented that in many parts of the world, the allergy season starts earlier and lasts longer each year, potentially because of climate change. Researchers have theorized that the more carbon dioxide in the atmosphere and the warmer the temperatures, the more plants produce flowers or food, which means more pollen.

The spring ragweed allergy season has lengthened by up to 27 days since 1995 depending on where you are in North America, according to research by the Agriculture Department published in the Proceedings of the National Academy of Sciences in 2011.

Higher latitudes are warming faster than those closer to the equator and are seeing proportionally longer pollen seasons, according to that study. For instance, in Saskatoon, Saskatchewan, the season was 27 days longer than the usual 44 days, while in Minneapolis, it was 16 days longer than the usual 62 days. By contrast, the effect in places such as Texas was minimal.

Lewis H. Ziska, a plant physiologist with the Agriculture Department’s crop system and global change laboratory and the study’s lead author, said the data his team has collected since then is consistent with the previous findings.

He said that this year’s long, frigid winter is especially intriguing to scientists because one of two extremes could happen: “It could be everything happening all at one time. In that case, there will be records for pollen count set. Or the damage to plants could be severe enough that you may not get much of a pollen season at all.”

Mark Scarupa, an allergist at the Institute for Asthma & Allergy, a medical practice in Montgomery County, agrees that it’s difficult to predict the severity of any allergy season. “Like the weatherman, we can get it wrong pretty bad,” he said.

Still, he said that in more than a decade of private practice, he has never seen an allergy season begin as late as this one. But like other local specialists, he said he expects that when pollen counts spike this spring, so will the number of patients seeking help.

“We have every expectation in the next week or two,” he said, “that we’re going to be flooded with people.”