San Francisco pollen forecast — Building 1 neighborhood
Pollen Today
Today (20 September) pollen in Building 1, San Francisco is moderate; ragweed is moderate; grass is low.
Pollen Tomorrow
Tomorrow (21 September 2026) grass remains low, ragweed remains moderate, mugwort at low levels.
7-Day Trend
Over the next week mugwort and ragweed will increase; grass 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) | Low | 12/100 |
| Willow (Salicaceae) | None | 0/100 |
| Mugwort (Artemisia) | None | 0/100 |
| Ragweed (Ambrosia) | Moderate | 30/100 |
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) | Low | 24/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | Low | 6/100 | |
| Ragweed (Ambrosia) | Moderate | 43/100 |
Local Environmental Conditions
Here, just outside the immediate area, a mix of coast live oak and bay laurel trees, oak in particular a notable spring allergen source. Located within easy reach, this area has a green space of mown lawn and planted trees, both feeding into local grass and ragweed counts. Local readings for the surrounding area tend to follow this same general pattern.
Average temperatures range from about 10°C in January to 18°C in August, and most of the 564 mm annual rainfall falls in the cooler months around January. Pollen activity typically picks up as temperatures climb out of the January low, from around February onward.
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Frequently Asked Questions About Pollen in California
Is pollen high in San Francisco right now?
On 20 September 2026, overall pollen levels in San Francisco are moderate. Ambrosia is the main contributor to airborne pollen, while grass remain at lower levels
Will pollen levels change in San Francisco tomorrow?
On 21 September 2026, pollen conditions in San Francisco will be different from today, with grass at low levels, ambrosia at moderate levels, artemisia at low levels
Is pollen expected to decrease in San Francisco this week?
According to the five-day outlook, grass pollen levels are expected to gradually decrease, while ambrosia and artemisia pollen will increase, suggesting mixed conditions later in the week.
Which pollen types are currently active in San Francisco?
On 20 September 2026, Ambrosia is the dominant pollen source in San Francisco. grass are also present but at lower levels. artemisia are not currently active.
When is pollen season in San Francisco?
How often is the San Francisco pollen forecast updated?
The San Francisco pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in San Francisco 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 Francisco 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 Francisco, 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).
