O'Fallon pollen forecast — Gettysburg neighborhood
Pollen Today
Today (20 September) pollen in Gettysburg, O'Fallon is high; ragweed is high; grass is moderate.
Pollen Tomorrow
Tomorrow (21 September 2026) grass declining, ragweed declining.
7-Day Trend
Over the next week grass, mugwort, and ragweed will increase.
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Pollen Risk
Today - 20 September
| Pollen species | Level | Value |
|---|---|---|
| Alder (Alnus) | None | 0/100 |
| Birch (Betula) | None | 0/100 |
| Hazel (Corylus) | None | 0/100 |
| Cypress (Cupressaceae) | None | 0/100 |
| Grass (Poaceae) | Moderate | 26/100 |
| Willow (Salicaceae) | None | 0/100 |
| Mugwort (Artemisia) | None | 0/100 |
| Ragweed (Ambrosia) | High | 51/100 |
Tomorrow - 21 September
| Pollen species | Level | Value | 7-Day Trend |
|---|---|---|---|
| Alder (Alnus) | None | 0/100 | — |
| Birch (Betula) | None | 0/100 | — |
| Hazel (Corylus) | None | 0/100 | — |
| Cypress (Cupressaceae) | None | 0/100 | — |
| Grass (Poaceae) | Low | 13/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | None | 0/100 | |
| Ragweed (Ambrosia) | Moderate | 37/100 |
Local Environmental Conditions
Gettysburg — Water here is bordered by hazel and willow, both notable sources of wind-borne pollen, some 451 meters to the edge of the area. Here, a short 215 meters out, woods composed largely of oak and birch, a combination tied to sharp spring pollen spikes. Here, at around 489m distant, parkland with regularly mown grass and planted trees, both sources of grass and ragweed pollen.
Water-edge hazel and willow are usually the first allergenic trees active here, topping out well before most other trees start releasing pollen, around February and March. The nearby oak and birch stands take the lead as spring progresses, topping out in the April-to-May stretch. Grass pollen takes over next, building to a peak around June, followed by ragweed's own peak stretch from mid-August into October.
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Pollen forecast neighborhoods 4 neighborhoods
Frequently Asked Questions About Pollen in Illinois
Is pollen high in O'Fallon right now?
On 20 September 2026, overall pollen levels in O'Fallon are high. Ambrosia is the main contributor to airborne pollen, while grass remain at lower levels
Will pollen levels change in O'Fallon tomorrow?
On 21 September 2026, pollen conditions in O'Fallon will be different from today, with ambrosia, grass continuing to decline
Is pollen expected to decrease in O'Fallon this week?
According to the five-day outlook, ambrosia, artemisia, and grass pollen levels will increase later in the week.
Which pollen types are currently active in O'Fallon?
On 20 September 2026, Ambrosia is the dominant pollen source in O'Fallon. grass are also present but at lower levels. artemisia are not currently active.
When is pollen season in O'Fallon?
How often is the O'Fallon pollen forecast updated?
The O'Fallon pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in O'Fallon come from nearby or far away?
Studies show that most pollen exposure (often 70–90%) comes from nearby sources, such as local trees and vegetation. A good pollen forecast therefore depends on accurately representing local vegetation. Pollen can travel long distances, but this usually matters only early in the season or during specific wind events.
Are pollen levels in O'Fallon based on measurements or forecasts?
Pollen data is often misunderstood. Most "pollen levels" are not real-time measurements, but forecasts.
Direct pollen measurements are typically delayed by 1-2 days because they require manual analysis. To show current conditions in O'Fallon, modern forecasts combine recent measurements, weather data, and information about local vegetation.
This allows us to estimate pollen levels for today and the coming days, not just report the past.
Airmine’s atmospheric monitoring platform was developed with support from the European Space Agency (ESA)’s Business Applications and Space Solutions (BASS) team, using satellite and Earth observation technologies to improve emissions monitoring.
Understanding the Scale
The 0–100 scores represent risk levels, not direct measurements of pollen or air pollutant concentrations. Higher scores indicate higher risk. Pollen and air quality use different thresholds.
Pollen
| None | 0 | No or negligible risk of exposure. Pollen/mold exposure is expected to be minimal. |
| Low | 0-25 | Low risk of exposure. Small amounts of pollen or mold spores may be present. |
| Moderate | 25-50 | Moderate risk of exposure. Pollen/mold exposure is expected to be noticeable. |
| High | 50-75 | High risk of exposure. Elevated pollen/mold exposure is expected. |
| Very High | 75-100 | Very high risk of exposure. Pollen/mold exposure is expected to be at or near its highest levels. |
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Get 15-day pollen forecasts with morning, afternoon and evening detail, plus 5-day air quality forecasts. Explore interactive pollen risk maps, estimated pollen season start, route profiles and a symptoms diary.
Features and forecast availability vary by region. Currently covering Europe, the contiguous US, southern Canada, South Africa, Australia, Indonesia (Java & Bali), Brazil, Paraguay, Uruguay and the Buenos Aires area.
Developed with support from the European Space Agency (ESA) Business Applications and Space Solutions (BASS).
