Pollen: Blame thunderstorms?

Rain ordinarily is the pollen-sufferer's best ally. To torment, pollen needs to fly, and rain is a wing-clipper.

Yet for the second consecutive day, the official tree-pollen count was "very high" in the 24-hour period that ended Tuesday morning.

In his daily blog, Dr. Donald J. Dvorin, allergist at The Asthma Center and the National Allergy Bureau's counter, said that despite the downpours they generated, those thunderstorms late last night might have been a factor.

Thunderstorm winds can lift and throw pollen about chaotically, he noted, and lightning can trigger "further anomalies" in the release of pollen.

As for the previous day's count, which covered the 24-hour period ending Monday morning, the pollen evidently defied the rain.

For those who track those online pollen forecasts, the counts for the last two days underscore the limits of their predictive abilities.

We noticed last week that the pollen.com forecast for Philadelphia called for pollen in the "low-moderate" range on Sunday and "medium" for Monday.

That made sense given the weather forecasts for a rainy Sunday and showery Monday. The "very high" results affirm that rain isn't the only agent.

Nailing pollen forecasts has proved to be an elusive pursuit for a variety of reasons. The atmosphere, everyone's favorite nonlinear chaotic system, is a clearly a driver, and dry, breezy days are best for flight.

But embedded in that capricious fluid's variability are the unpredictable rhythms of reproduction. Pollen is a tree's way of sowing the seeds for future generations.

Experts point out that trees appear to expend more reproductive "effort" from year to year.

Thus, the overall volume of tree pollen can vary radically from one year to the next, complicating forecasting and trend-spotting.

For example, based on asthma center data, the volume of tree pollen in 2008 was triple what it was in 2007.

Dvorin, who has been doing the counting for 30 years, has said he believes that overall volume has been increasing.

Three decades isn't a huge sampling, and not enough to draw conclusion about trends and whether any trends are related to worldwide warming.

What is known for now is that for the allergic, rain won't not necessarily stop the sneezing.