Gilroy pollen forecast - today, tomorrow and the week ahead
Pollen Today
Today (20 September) pollen in Gilroy is high; grass and ragweed are high; mugwort is low.
Pollen Tomorrow
Tomorrow (21 September 2026) mugwort remains low, ragweed remains high, grass 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) | High | 51/100 |
| Willow (Salicaceae) | None | 0/100 |
| Mugwort (Artemisia) | Low | 2/100 |
| Ragweed (Ambrosia) | High | 65/100 |
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) | Low | 2/100 | |
| Ragweed (Ambrosia) | High | 65/100 |
Local Environmental Conditions
Gilroy's parks, including Christmas Hill Park and the Uvas Creek corridor, feature oak, eucalyptus, and introduced trees as the main pollen sources, with exposure varying between these green areas and the more built-up city centre. Surrounding Santa Clara Valley farmland and the Diablo and Santa Cruz Mountain foothills contribute substantial grass and crop pollen, while the valley setting channels prevailing northwesterly winds and marine air from the San Francisco Bay.
Gilroy's pollen season opens with acacia and tree pollen from January in the mild Santa Clara Valley climate. Oak follows through March and April, with grass peaking strongly through April and May from the surrounding agricultural valley. The valley setting channels prevailing northwesterly winds and marine air from San Francisco Bay, while surrounding farmland and the Diablo and Santa Cruz Mountain foothills contribute substantial grass and tree pollen.
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Frequently Asked Questions About Pollen in California
Is pollen high in Gilroy right now?
On 20 September 2026, overall pollen levels in Gilroy are high. Grass is the main contributor to airborne pollen, while ambrosia and artemisia remain at lower levels
Will pollen levels change in Gilroy tomorrow?
On 21 September 2026, pollen conditions in Gilroy will be different from today, with artemisia at low levels, ambrosia at high levels and grass continuing to decline
Is pollen expected to decrease in Gilroy 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 Gilroy?
On 20 September 2026, Grass is the dominant pollen source in Gilroy. ambrosia and artemisia are also present but at lower levels.
When is pollen season in Gilroy?
How often is the Gilroy pollen forecast updated?
The Gilroy pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in Gilroy 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 Gilroy 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 Gilroy, 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).
