San Jose pollen forecast — Willow Glen neighborhood
Pollen Today
Today (20 September) pollen in Willow Glen, 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 | 28/100 |
| 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 | 35/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | Low | 4/100 | |
| Ragweed (Ambrosia) | High | 70/100 |
Local Environmental Conditions
Willow Glen is a silicon Valley with valley oak, ornamental cherry, and grass lawns. Spring pollen season is robust from March through May; oak and olive are major sources. Valley topography traps pollen on hot, still days.
Willow Glen tracks San Jose's broader pollen pattern, with acacia and oak appearing from January before olive takes over and peaks through February and March. Grass pollen builds through March and April, and weed pollen lingers into early autumn once grass season ends. The region's Mediterranean pattern keeps winters mild and wet, springs pollen-heavy, and summers largely pollen-free.
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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 ambrosia at high levels, artemisia at low levels, grass at moderate 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 artemisia and grass 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).
