Millbrae pollen forecast - today, tomorrow and the week ahead
Pollen Today
Today (20 September) pollen in Millbrae is high; ragweed is high; grass is low.
Pollen Tomorrow
Tomorrow (21 September 2026) ragweed remains high, grass increasing, mugwort at low levels.
7-Day Trend
Over the next week mugwort will increase; grass and ragweed will decrease.
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Features and forecast availability vary by region.
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 | 20/100 |
| 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 | 30/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | Low | 8/100 | |
| Ragweed (Ambrosia) | High | 70/100 |
Local Environmental Conditions
Here, a short distance from here, a waterway supports coast live oak and sycamore along its bank, both notable sources of wind-borne pollen. This area, in the surrounding area, has woodland dominated by coast live oak and bay laurel, with oak a leading regional tree-pollen allergen. A park whose lawns and ornamental trees quietly add to grass and ragweed pollen levels; this sits not far from here.
Average temperatures range from about 11°C in March to 17°C in September, and most of the 551 mm annual rainfall falls in the cooler months around March. Pollen activity typically picks up as temperatures climb out of the March low, from around April onward.
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Frequently Asked Questions About Pollen in California
Is pollen high in Millbrae right now?
On 20 September 2026, overall pollen levels in Millbrae are high. Ambrosia is the main contributor to airborne pollen, while grass remain at lower levels
Will pollen levels change in Millbrae tomorrow?
On 21 September 2026, pollen conditions in Millbrae will be different from today, with ambrosia at high levels, artemisia at low levels and grass increasing
Is pollen expected to decrease in Millbrae 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 Millbrae?
On 20 September 2026, Ambrosia is the dominant pollen source in Millbrae. grass are also present but at lower levels. artemisia are not currently active.
When is pollen season in Millbrae?
How often is the Millbrae pollen forecast updated?
The Millbrae pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in Millbrae 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 Millbrae 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 Millbrae, 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).
