Why the weather has led to a rapid increase in allergies
If you stepped outside today to enjoy the noticeably warmer weather, you likely noticed two things: temperatures in the mid to upper 70s and a sudden, aggressive case of itchy eyes or a stuffy nose. While the sky over Mid-Missouri remains clear, we are currently in the middle of a large atmospheric event that you can't see, but you can certainly feel.
As we reach the final full day of winter, the transition into spring isn't just a date on the calendar; it's a biological explosion triggered by specific meteorological thresholds. This is why it feels like a peak allergy day in the middle of May, even though it is still March.
Meteorologists and botanists track a metric called accumulated growing degree days. This measures the amount of heat that has built up over time. After the bitter cold we experienced earlier this month, the sudden surge into the upper 70s has acted like a biological "on-switch" for Missouri's native trees.
Specifically, we are seeing a process called anthesis. This is the exact moment when the reproductive parts of the plants, like the cones on local cedar and juniper trees or the buds on elms, fully expand to release their pollen. Since we jumped from freezing temperatures to nearly 80 degrees in such a short window, these trees aren't releasing their pollen in a slow trickle. They are releasing their entire seasonal load in a singular, massive "pulse".
It isn't just the amount of pollen that's the problem; it's how the atmosphere is moving it. Today's weather has created the perfect transport mechanism for these microscopic grains. With low humidity hovering around 20-30% today, the air is incredibly dry. When pollen is dry, it is lighter and more "loftable," meaning it can stay suspended in the air for much longer periods. The southwest winds bringing the warmer temperatures are another reason why this is occurring. The wind is acting like a conveyor belt, carrying pollen from the large cedar forests of the Ozarks directly into our neighborhoods.
While it's tempting to think winter is over, today is technically the final full day of the season. Tomorrow morning, the Spring Equinox officially arrives. However, this "pollen pulse" is a classic occurrence of false spring. Missouri's median last frost date isn't until mid-April. This sudden warmth has tricked the vegetation into an early awakening, which could lead to agricultural heartbreak if (and when) we see our next hard freeze. For now, pollen will remain high as long as these south winds and dry conditions persist.
For now, to beat the allergies, keeping windows shut will keep the microscopic pollens from entering. Also, pollen counts are often highest during the morning, but the grains settle as the wind dies down at night. Showering before bed ensures you aren't sleeping in the day's "transport." Finally, wait on washing your car, as these wind conditions paired with the high volume of anthesis will lead to that yellow film on your windshield returning within the following hour.
