Redwood City pollen forecast - today, tomorrow and the week ahead
Pollen Today
Today (20 September) pollen in Redwood City 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 mugwort will increase; grass and 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 | 56/100 |
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 | 45/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | Low | 8/100 | |
| Ragweed (Ambrosia) | High | 68/100 |
Local Environmental Conditions
Redwood City's parks and the San Francisquito 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 Peninsula hills and the San Francisco Bay shoreline contribute substantial grass and tree pollen, while prevailing westerly winds carry marine air that can periodically disperse pollen across the city.
Redwood City's pollen season opens with acacia and tree pollen from January in the mild San Francisco Peninsula climate. Oak follows through March and April, with grass peaking through April and May. The San Francisco Bay position means onshore westerly winds frequently disperse pollen, while the Peninsula hills contribute substantial grass and tree pollen under offshore conditions. The dry summer largely suppresses mid-season pollen across the city.
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Pollen forecast neighborhoods 1 neighborhood
Frequently Asked Questions About Pollen in California
Is pollen high in Redwood City right now?
On 20 September 2026, overall pollen levels in Redwood City are high. Ambrosia is the main contributor to airborne pollen, while grass remain at lower levels
Will pollen levels change in Redwood City tomorrow?
On 21 September 2026, pollen conditions in Redwood City will be different from today, with ambrosia at high levels, artemisia at low levels, grass at moderate levels
Is pollen expected to decrease in Redwood City this week?
According to the five-day outlook, ambrosia and grass pollen levels are expected to gradually decrease, while artemisia pollen will increase, suggesting mixed conditions later in the week.
Which pollen types are currently active in Redwood City?
On 20 September 2026, Ambrosia is the dominant pollen source in Redwood City. grass are also present but at lower levels. artemisia are not currently active.
When is pollen season in Redwood City?
How often is the Redwood City pollen forecast updated?
The Redwood City pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in Redwood City 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 Redwood City 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 Redwood City, 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).
