The Pollen Count: How Weather Conditions Affect Seasonal Allergies

As I sit here writing this week’s blog post, I continue to hope that *writing* about springtime will mean that actual springlike weather conditions will occur outside my (deceptively) sunny window. Now that it is April, seasonal allergies are in full swing for many, even up into the northern parts of the United States where full leaf-out is still a few weeks away (see our blog post on phenology for more information on that). Although most of us allergy sufferers are fully aware that there is a seasonal pattern to allergies, it is less commonly known why some seasons are just terrible, while others aren’t as bad.

Let’s start with a little bit of background on what is commonly known as ‘the pollen count’. Did you know that the American Academy of Allergy, Asthma, and Immunology (AAAAI) has a branch called the National Allergy Bureau which is entirely devoted to reporting levels of pollen and mold spores? This group is largely staffed by volunteers who use air sampling equipment to report levels at 84 stations across the United States. These samples are examined under a microscope to obtain actual measurements of what is present in the atmosphere each day.

Microscopic view of ragweed pollen. Courtesy AAAAI/NAB.

This data is displayed in an easy-to-read graphical display for each location where the pollen count is measured. If the counts are very low at a particular site (such as very early in the spring), the display is not available that day. You can see here that as of today’s writing, there are very high concentrations of several types of tree pollen in the Pittsburgh, Pennsylvania area, although grasses and weeds were not present. Grass pollen counts tend to increase later in the spring, while trees peak during the early spring.

Pollen counts for Pittsburgh, PA on 4/3/2019. Courtesy AAAAI/NAB.

One can also click on the ‘View Calendar of Data’ link to see trends in the daily pollen counts at each site. Below is the March 2019 calendar for Atlanta, Georgia. This site, being located in the Southeast, is farther ahead in the allergy season than those sites in the Northeast US.

Calendar of pollen counts for Atlanta, GA for March 2019. Courtesy AAAAI/NAB.

The actual ‘pollen count’ is a different product than what many companies produce, which is a pollen forecast. Both parameters can be useful. The actual pollen count is reflective of what is currently in the air on any given day, and looking at the trends on the calendar can help allergy sufferers prepare or alleviate symptoms by taking allergy medications. The pollen forecast is exactly what it sounds like – similar to a weather forecast, pollen forecasts generally use parameters such as pollen counts from prior years and current weather forecasts to estimate what pollen counts will be in the coming days. Just as with weather forecasts, there are numerous companies which produce pollen forecasts.

This week’s pollen count forecast for Atlanta, GA. Courtesy The Weather Channel.

Back to the original question: how do the weather conditions affect pollen levels? Generally speaking, dry and/or windy conditions tend to increase pollen counts, while rain can remove some of the pollen from the atmosphere, offering a temporary respite for those with allergies. Seasonal weather trends also matter. For example, rain during the late summer or early fall can actually increase tree pollination and result in higher pollen levels the following spring ( The faster the onset of spring weather conditions is, the more severe and rapid the onset of allergy season is. For example, here in the northeast, last spring finally we saw some mild conditions in late April after a very cold and snowy March. That resulted in many trees putting out buds and leaves at a rapid rate as the weather quickly warmed, and the onset of allergy symptoms was quick and severe for many of us. This year, March has been less snowy with seasonable, and even below normal, temperatures. Thus, while the trees have buds, the pollen counts have not increased as dramatically as they had by this time last year.

Finally, the effects of our changing climate on pollen counts and allergies is currently an area of study. The Allergy and Asthma Foundation of America (AAFA) reports that pollen season increased in length by between 11 and 27 days between 1995 and 2011 across the United States. The results of a survey of allergy specialists’ views on the health affects of climate change can be found here. Most specialists recommend that sufferers monitor pollen counts and begin taking their medication before the onset of symptoms to minimize the allergic reaction, as well as avoiding exposure to outdoor allergens on days when the pollen count is very high. Of course, consult with your doctor or specialist to determine the best ways to manage your particular seasonal allergy symptoms.

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