San Marcos pollen forecast — San Elijo Hills neighborhood
Pollen Today
Today (20 September) pollen in San Elijo Hills, San Marcos is high; ragweed is high; grass is moderate; mugwort is low.
Pollen Tomorrow
Tomorrow (21 September 2026) ragweed remains high, grass declining, mugwort no longer expected.
7-Day Trend
Over the next week grass, mugwort, and ragweed will increase.
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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 | 35/100 |
| Willow (Salicaceae) | None | 0/100 |
| Mugwort (Artemisia) | Low | 8/100 |
| Ragweed (Ambrosia) | High | 68/100 |
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 | 25/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | None | 0/100 | |
| Ragweed (Ambrosia) | High | 59/100 |
Local Environmental Conditions
Located near this part of town, this area has coast live oak and sycamore grow along the bank, contributing some of the season's tree pollen. Located close to this spot, this area has forest where coast live oak and madrone make up much of the canopy, driving local spring pollen counts.
Average temperatures range from about 11°C in January to 26°C in August, and most of the 334 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 Marcos right now?
On 20 September 2026, overall pollen levels in San Marcos are high. Ambrosia is the main contributor to airborne pollen, while grass and artemisia remain at lower levels
Will pollen levels change in San Marcos tomorrow?
On 21 September 2026, pollen conditions in San Marcos will be different from today, with ambrosia at high levels and grass continuing to decline
Is pollen expected to decrease in San Marcos this week?
According to the five-day outlook, artemisia, grass, and ambrosia pollen levels will increase later in the week.
Which pollen types are currently active in San Marcos?
On 20 September 2026, Ambrosia is the dominant pollen source in San Marcos. grass and artemisia are also present but at lower levels.
When is pollen season in San Marcos?
How often is the San Marcos pollen forecast updated?
The San Marcos pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in San Marcos 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 Marcos 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 Marcos, 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).
