San Jose pollen forecast - today, tomorrow and the week ahead
Pollen Today
Today (20 September) pollen in San Jose is high; ragweed is high; grass is moderate.
Pollen Tomorrow
Tomorrow (21 September 2026) grass remains moderate, ragweed remains high, mugwort at low levels.
7-Day Trend
Over the next week grass and mugwort will increase; ragweed will decrease.
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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 | 33/100 |
| Willow (Salicaceae) | None | 0/100 |
| Mugwort (Artemisia) | None | 0/100 |
| Ragweed (Ambrosia) | High | 62/100 |
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 | 39/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | Low | 4/100 | |
| Ragweed (Ambrosia) | High | 69/100 |
Local Environmental Conditions
San Jose's valley floor vegetation, anchored by Alum Rock Park and the Guadalupe River corridor, features oak, ash, and walnut as the main tree pollen sources, with exposure varying between these green areas and the more built-up city centre. Surrounding Santa Clara Valley farmland and the oak woodland of the Diablo Range and Santa Cruz Mountains contribute substantial grass and tree pollen when winds blow from the east and south.
San Jose's pollen season opens with acacia and tree pollen from January in the mild Santa Clara Valley climate. Oak and walnut follow through March and April, with grass peaking through May and June. The flat valley setting allows substantial farmland grass pollen to accumulate, while the surrounding Diablo Range and Santa Cruz Mountains contribute oak and grass pollen when winds blow from the east and south.
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Resource Hub
Pollen forecast neighborhoods 80 neighborhoods
Sports venues in San Jose 1 sports venue
Popular Local Routes 1 route
Frequently Asked Questions About Pollen in California
Is pollen high in San Jose right now?
On 20 September 2026, overall pollen levels in San Jose are high. Ambrosia is the main contributor to airborne pollen, while grass remain at lower levels
Will pollen levels change in San Jose tomorrow?
On 21 September 2026, pollen conditions in San Jose will be different from today, with grass at moderate levels, ambrosia at high levels, artemisia at low levels
Is pollen expected to decrease in San Jose this week?
According to the five-day outlook, ambrosia pollen levels are expected to gradually decrease, while grass and artemisia pollen will increase, suggesting mixed conditions later in the week.
Which pollen types are currently active in San Jose?
On 20 September 2026, Ambrosia is the dominant pollen source in San Jose. grass are also present but at lower levels. artemisia are not currently active.
When is pollen season in San Jose?
How often is the San Jose pollen forecast updated?
The San Jose pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in San Jose 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 San Jose 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 San Jose, 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).
