Greencastle pollen forecast - today, tomorrow and the week ahead
Pollen Today
Today (20 September) pollen in Greencastle is moderate; grass and ragweed are moderate; mugwort is low.
Pollen Tomorrow
Tomorrow (21 September 2026) ragweed remains moderate, grass declining, mugwort no longer expected.
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 | 28/100 |
| Willow (Salicaceae) | None | 0/100 |
| Mugwort (Artemisia) | Low | 2/100 |
| Ragweed (Ambrosia) | Moderate | 49/100 |
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 | 9/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | None | 0/100 | |
| Ragweed (Ambrosia) | Moderate | 29/100 |
Local Environmental Conditions
Set on rolling farmland in west-central Indiana, Greencastle's landscape is defined by oak-hickory forest alongside sugar maple and farmland crops, the main contributors to seasonal pollen exposure. Exposure varies with proximity to green space versus the more built-up parts of Greencastle. The mix of native and introduced species here is fairly typical for this part of the country.
Pollen season in Greencastle starts with maple and elm in March before oak extends the tree season through April. A grass pollen peak follows through May and June; ragweed extends the season into September. The continental Midwest climate produces a well-defined spring tree peak followed by a strong late-summer ragweed season, a defining feature of the local season.
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Frequently Asked Questions About Pollen in Indiana
Is pollen high in Greencastle right now?
On 20 September 2026, overall pollen levels in Greencastle are moderate. Grass is the main contributor to airborne pollen, while ambrosia and artemisia remain at lower levels
Will pollen levels change in Greencastle tomorrow?
On 21 September 2026, pollen conditions in Greencastle will be different from today, with ambrosia at moderate levels and grass continuing to decline
Is pollen expected to decrease in Greencastle this week?
According to the five-day outlook, grass, ambrosia, and artemisia pollen levels will increase later in the week.
Which pollen types are currently active in Greencastle?
On 20 September 2026, Grass is the dominant pollen source in Greencastle. ambrosia and artemisia are also present but at lower levels.
When is pollen season in Greencastle?
How often is the Greencastle pollen forecast updated?
The Greencastle pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in Greencastle 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 Greencastle 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 Greencastle, 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. |
Get More in the Airmine Pollen app
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).
