Cathedral Basilica of Saint Joseph, San Jose Mold Forecast - Today, Tomorrow and the Week Ahead
Mold Today
Today (10 October) mold in Cathedral Basilica of Saint Joseph, San Jose is low; alternaria and cladosporium are low.
Mold Tomorrow
Tomorrow (11 October 2026) levels are similar to today.
7-Day Trend
Over the next week alternaria and cladosporium will increase.
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Mold Risk
Today - 10 October
| Mold species | Level | Value |
|---|---|---|
| Alternaria | Low | 11/100 |
| Cladosporium | Low | 18/100 |
Tomorrow - 11 October
| Mold species | Level | Value | 7-Day Trend |
|---|---|---|---|
| Alternaria | Low | 8/100 | Steady |
| Cladosporium | Low | 13/100 | Steady |
Local Mold Conditions
Organic material for mold is moderately available around this part of San Jose, mostly in the green spaces among the buildings. In the built-up parts, organic material is more scattered: garden waste, compost, mulch, lawn clippings and leaves from street trees. Banks and low ground beside a stream or river stay wet enough for plant debris to break down quickly.
The mold season is led by Cladosporium, which thrives on compost, mulch and leaves through most of the year and peaks in October, at roughly 17°C. The cooler climate keeps Alternaria fairly low, with a small peak in September. January is usually the quietest month, at around 9°C. Day to day, spores peak on dry, breezy afternoons after dew or light rain.
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Resource Hub
Mold forecast neighborhoods 80 neighborhoods
Sports venues in San Jose 1 sports venue
Frequently Asked Questions About Mold in California
Why do I still have allergy symptoms after the pollen season?
Allergy symptoms after the main pollen season may be caused by mold spores. Outdoor mold levels can remain high into late summer and autumn, when pollen levels are already falling. Mold allergy can cause symptoms similar to pollen allergy, including sneezing, a runny or blocked nose, itchy eyes, coughing, and wheezing.
What are mold spores and why do they cause allergies?
Mold spores are tiny particles released by fungi into the air. When inhaled, they can trigger an allergic reaction in sensitive people. Common symptoms include sneezing, a runny or blocked nose, itchy or watery eyes, coughing, and wheezing.
When are mold spore levels highest?
Outdoor mold spore levels often increase during warm and humid conditions, particularly when there is plenty of decaying vegetation. Levels can vary considerably with weather, season, vegetation, and location, and some types of mold are more common during particular times of the year, e.g. in the Fall.
How can I reduce my exposure to mold spores?
If you are sensitive to mold, check local mold spore levels and forecasts before spending long periods outdoors. On high-risk days, reducing time around dense vegetation, compost, fallen leaves, and other sources of decaying plant material may help limit exposure.
Understanding the Scale
The 0–100 mold scores represent risk levels, not direct mold measurements. Higher scores indicate higher risk.
Mold
| 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. |
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