We are in the heart of one of the region's most underrated aesthetic seasons. The late-day light playing upon the tree tops is ever more spectacular. The still-bare branches are showing off their architecture, limbs subtly colored with swollen buds.
With last week's cold snap a fading memory, temperatures will soon nudge toward 60, the winds will blow moderately - and those trees will become a source of torment to countless allergy sufferers.
The Inquirer plans to resume publication of daily pollen counts on the weather page Thursday, and my daily blog will deal with them as well.
But sensitive noses are aware that tree-pollen season already is under way.
How bad will it be this year?
You're welcome to check out all the online pollen forecasts, but be warned that they are trying to get a handle on two of the most elusive forces on Earth: weather and sex.
We can say with certainty that the region's trees will eject mass quantities of pollen into the air as part of their annual lovefest from now to mid-May. The details are another matter.
As many as 100 species of trees send out the homely grains, some so tiny they are invisible to the naked eye. If they land on the ground, under the right circumstances they will become trees. If they land in the nose of an allergy sufferer, they will become annoying.
This I can say from long, personal experience. Doing research in an otherwise quiet library archive I can recall having a sneezing fit that qualified as disturbing the peace. Once, while watching a play in a small theater, I sneezed so many times that the person next to me kindly asked me to leave.
That was my wife - one of the robust majority who remain blissfully unaffected by the private lives of trees. For them, pollen is harmless.
But for an estimated one million people in the Philadelphia region alone, for reasons no one can figure out, the immune system views a pollen grain as a mortal enemy. It sends out a special antibody when the airborne allergen lands on the mucous membranes lining the nose. When the antibody comes in contact with a pollen grain, it fights back with an inflammatory chemical such as histamine.
The result? In an onomatopoeia: Ah-chooooo!
It is impossible to say when an individual's torment will start.
Some folks started complaining two weeks ago, said Donald J. Dvorin, an allergy specialist and the region's official pollen counter for the American Academy of Allergy, Asthma, and Immunology. It is his counts that appear in The Inquirer.
The pollen count estimates the number of pollen grains that would pass through a refrigerator-sized parcel of air during a 24-hour period.
The counting itself is labor-intensive and complicated.
Dvorin, who is in private practice at the Asthma Center, places what are called Burkhard Traps - devices that capture pollen on a glass slide - on roofs in Center City and Cherry Hill. He examines the slides under a microscope every weekday morning.
The counts are a day old when they reach print - rough ranges will be posted earlier, at www.asthmacenter.com - but they still give a decent indication of the state of the season.
Based on the counts from past years, the trees will get serious about propagation this week. But the seasonal kickoff can vary. In 1998, the party didn't get going until late March. In 2000, it was in full swing by the middle of the month.
Another variable is the so-called reproductive effort. Some years the trees go all-out, and in others they bide their time. In 1999, for example, the counts indicated that local trees ejected twice as much pollen as they had the previous year.
Again, no one is sure why. Estelle Levetin, a biology professor at Tulsa University in Tulsa, Okla., thinks it has something to do with weather conditions in the preceding seasons.
Levetin has been studying pollen for 27 years. She has tried her hand at forecasting ragweed - its turn comes in late summer - but feels overmatched by trees, which are far more complex than the humble weed.
Pollen forecasts are only as good as weather forecasts, and those get weaker the further in advance they are attempted.
As a rule, warm days with winds from 13 to 17 m.p.h. are ideal for transporting pollen. But what if the trees are not in the mood? What if it rains?
A sudden shower will wash pollen out of the air. Humidity is also a factor in pollen movement: the drier the better.
"There's such a variability that it is amazing," said Dvorin. The private Asthma Center, which has offices in Center City and five other locations on both sides of the river, has eschewed pollen predicting entirely.
"I, personally, have little faith in the pollen forecasting," agreed David Shulan, an allergy specialist in Albany, N.Y.
Yet even the forecasting sites would concur on one point: The season is upon us.
Let the sneezing begin.
Health & Science Blogs
Anthony R. Wood's climatic comments: http://go.philly.com/weatherornot
Sandra Long's experience as an African American woman with breast cancer: http://go.philly.com/sandra
Contact staff writer Anthony R. Wood at 610-313-8210 or firstname.lastname@example.org.