Glendora pollen forecast - today, tomorrow and the week ahead
Pollen Today
Today (20 September) pollen in Glendora is high; grass and ragweed are high; mugwort is low.
Pollen Tomorrow
Tomorrow (21 September 2026) ragweed remains high, 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) | High | 70/100 |
| Willow (Salicaceae) | None | 0/100 |
| Mugwort (Artemisia) | Low | 20/100 |
| Ragweed (Ambrosia) | High | 70/100 |
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) | Moderate | 50/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | None | 0/100 | |
| Ragweed (Ambrosia) | High | 55/100 |
Local Environmental Conditions
Glendora's San Gabriel Valley foothill California setting features walnut, coast live oak, and blue gum eucalyptus as the main tree pollen sources, with exposure varying between the San Gabriel Mountain foothills chaparral residential areas and the more built-up commercial corridors along Route 66. The San Gabriel River corridor provides locally significant green space, while the Southern California Black Walnut woodland on the hillsides contributes a distinctive native pollen source and the mountain backdrop creates downslope Santa Ana wind conditions.
Glendora's San Gabriel Valley foothill setting produces a season opening in January with olive and walnut before grass from surrounding land peaks through March and April. Mugwort extends exposure into September, while the foothill setting means slightly higher temperatures than in coastal cities and the San Gabriel Mountain backdrop concentrates pollen under downslope Santa Ana wind conditions throughout the season.
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Frequently Asked Questions About Pollen in California
Is pollen high in Glendora right now?
On 20 September 2026, overall pollen levels in Glendora are high. Grass is the main contributor to airborne pollen, while ambrosia and artemisia remain at lower levels
Will pollen levels change in Glendora tomorrow?
On 21 September 2026, pollen conditions in Glendora will be different from today, with ambrosia at high levels and grass continuing to decline
Is pollen expected to decrease in Glendora this week?
According to the five-day outlook, artemisia, grass, and ambrosia pollen levels will increase later in the week.
Which pollen types are currently active in Glendora?
On 20 September 2026, Grass is the dominant pollen source in Glendora. ambrosia and artemisia are also present but at lower levels.
When is pollen season in Glendora?
How often is the Glendora pollen forecast updated?
The Glendora pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in Glendora 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 Glendora 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 Glendora, 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).
