Worst of tree pollen season may be over

On Thursday, the tree pollen spiked to 2871 grains per cubic meter, as astonishing level unsurpassed since 2010. The good news for allergy sufferers? It may now be on the way down.

Weekend levels dropped off significantly from Thursday’s count (measured Friday morning).  The counts for Friday, Saturday, and Sunday (measured Saturday, Sunday and Monday morning)  each took big steps back according to Susan Kosisky, director of the U.S. Army Centralized Allergen Extract Lab. Friday’s count was 1,969, Saturday 425,  and Sunday 283.

The drop in temperatures following a cold front Friday played a helping hand in the drop off, Kosisky said.

The cause of Thursday’s spike

The combination of warmth, wind and sun Thursday that followed relatively cool conditions prior triggered the huge tree pollen onslaught late last week.

“Everything was pent up due to the colder temps,” Kosisky said.

But the pollen exploded once Thursday’s southerly breeze kicked in, the sun burst out, and temperatures shot up to near 80.

“When it gets up to near 80, it’s optimal for pollen and when you get the wind, it can really open things up,” Kosisky said.

Kosisky explained pollen is released from little sacks (known as anther sacks) that dry and crack more easily when it’s warm and sunny.

“If it’s windy, it just facilitates the pollen being carried long distances,” Kosisky said.

If there’s any consolation for allergy sufferers, the Thursday count may have been this year’s peak, with declining levels looking ahead, Kosisky said. There’s only so much pollen for the trees to release.

“I kind of feel that might be the high count,” Kosisky said. “Once it’s blows, it’s done for the season.  There’s just not much left.”

Although they may have peaked locally, Kosisky said we should continue to see some high levels into early May.

“Some later-pollinating trees to include hickory and walnut will be flowering soon, and I suspect there are plenty of abundant pollen producers such as oak and pine around to keep those levels high,” she said. But the good news is that “the trees have really started to leaf now, which assists in obstructing the pollen from being released so easily into the air.”

By the second half of May, levels should more radically wane.

“In the past we usually see tree count levels really starting to drop off the 3rd week in May where daily average counts drop to about 50 grains/cubic meter of air,” she said.

If Thursday’s 2870 count was this year’s peak, it occurred close to prime time.  The last week of April is the average period for peak tree pollen in Washington but there is considerable year-to-year variability.  Last year, due to unusually warm weather early in the season, the peak occurred on March 28.

 

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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Jason Samenow · April 22, 2013