Castro Valley, CA Pollen Count
Castro Valley, CA · Last updated Friday, November 6, 2026
This page shows the most recent reading available for Castro Valley — from Friday, November 6, 2026 (1 day ago) — not today's reading.
Pollen Overview
Today's overall pollen level and the dominant type (trees, weeds, grass, or mold).
Total Pollen Index
The combined pollen level across all types (0–100).
Castro Valley, CA
Weeds Index
How active weeds pollen is today (0–100).
Castro Valley, CA
Pollen Types
Pick a pollen subtype to update the species forecast
5-Day Castro Valley Overall Pollen Forecast
Bars are colored by severity (Low/Moderate/High).
Pollen count Castro Valley residents check each morning
The Castro Valley pollen count today is 25 (Low). The main driver is Ragweed, with weed pollen at 29 today. That total sits on a narrow base: weed pollen is 29 while tree pollen is just 25 and grass pollen 1. Plant-by-plant detail for Castro Valley, CA follows, along with the outlook for the days ahead. Pollen Atlas updated this count on Friday, November 6, 2026.
A Low band on the Pollen Atlas index means the Total Pollen Index has stayed in the lower part of the 0–100 scale. Readings in this band are built from low individual category values rather than from one large spike, and the category split above matters more than the headline number: a low total can still contain one category, such as weed pollen or mold, reading noticeably higher than the rest, which is why the split is printed on every Castro Valley page.
Fall is ragweed season across most of the United States: ragweed plants release pollen from late summer into autumn, and weed pollen is typically the last major outdoor pollen category to fade as the weather cools. That pattern is why an autumn total is so often weed-led even when the headline number is low — tree and grass pollen have usually receded by then, leaving weed pollen, and on damp days mold, to make up most of what the index records.
To see whether today’s pollen level holds, check the 5-day Castro Valley pollen forecast below — it is currently mixed, with Monday the highest day in the window.
This is the pollen count Castro Valley residents check each morning, built from the day’s tree, grass, weed and mold readings.
What is the Castro Valley pollen count today?
The Castro Valley pollen count today is 25 out of 100 (Low) on the Pollen Atlas Total Pollen Index, driven mainly by Ragweed.
Short answer for anyone searching pollen count today Castro Valley: this page is updated every morning with the day’s modelled reading.
Castro Valley allergies today
Castro Valley allergies today are set by the same reading as the pollen count above: the Total Pollen Index is 25 (Low), driven mainly by Ragweed. When people ask about Castro Valley allergies, this is the number that answers them — one daily index built from today’s tree, grass, weed and mold readings for Castro Valley.
Allergies in Castro Valley follow the California calendar set out below — the chapters, the plants behind them, and the 5-day forecast on this page show whether today is typical for the season or an exception to it. If you are checking allergies today in Castro Valley before heading outdoors, the split at the top of this page is the part to read: it shows which pollen is doing the work today, not just how high the total sits.
Read the five-day table on this page as the Castro Valley allergy forecast: today reads 25 (Low), and the day-by-day outlook shows whether Castro Valley allergies are set to ease or build across the week — the days to plan outdoor time around are the ones where the index steps down, not just today.
In practice, the allergy count Castro Valley today records is this same combined reading — tree, grass, weed and mold in one index.
The Castro Valley allergy count today is 25 (Low) — the same Total Pollen Index as the pollen count above, in one combined reading.
Pollen count today Castro Valley: the 5-day forecast
| Day | Total Pollen Index | Band |
|---|---|---|
| Friday, November 6 | 25 | Low |
| Saturday, November 7 | 24 | Low |
| Sunday, November 8 | 24 | Low |
| Monday, November 9 | 27 | Low |
| Tuesday, November 10 | 24 | Low |
Pollen Atlas forecasts Castro Valley’s pollen count to peak on Monday at 27 (Low) over the next 5 days.
Pollen by type in Castro Valley
What is driving Castro Valley’s pollen today
The shape of today’s 25 (Low) is set by weed pollen at 29 (Low on its own scale) — about 53% of the four category readings added together, 4 points clear of the next category, tree pollen at 25. A weed-led total is the classic late-year shape: tree and grass pollen have usually receded, leaving weed pollen — and on damp days mold — to make up most of what the index records. Weed pollen leading in November runs against the usual calendar — the California weed chapter runs August to October — so today’s lead is the model outranking the pattern, and this page reports the modelled reading first.
Plant-level detail is not in today’s feed for Castro Valley, so the drivers have to be read from the category split above. The California guide’s account of California names planted olive and the Central Valley’s concentrated spring pollen — the pollens behind readings of this shape in this state — and the split shows how much of today’s total each category is actually carrying.
Across the five-day window the Total Pollen Index runs from 24 to 27, never changing band. Today’s 25 sits 0 points above the window’s average of 24.8 — a steady window, in which one day reads much like the next.
Plants affecting Castro Valley now
Detailed plant-by-plant readings for Castro Valley were not returned in today\u2019s source data, so this section summarises the pollen types the index above is built from instead of listing individual plants.
Tree pollen is one of the categories with a non-zero reading today, at 25 (Low).
Grass pollen is one of the categories with a non-zero reading today, at 1 (Low).
Weed pollen is one of the categories with a non-zero reading today, at 29 (Low).
In the California pattern, the plants that typically shape this city’s year are winter and spring trees, late-spring grasses and late-summer weeds — named here as regional context only, not as today\u2019s measurements.
Plant detail returns here automatically on any day the source data includes it.
Every pollen type, with photos and seasons: the pollen directory.
Castro Valley pollen through the year
Chapter by chapter, the Castro Valley pollen year runs like this:
- Trees build through spring, with planted olive peaking from March into May.
- Grasses peak in spring in the Central Valley and run longer and milder on the coast.
- Weeds follow in late summer and fall, stronger after wet winters.
The California allergy season guide names planted olive and the Central Valley’s concentrated spring pollen. There is no single California season: the Central Valley records some of the state’s sharpest spring peaks, trapped and concentrated by valley geography, while the coast runs long and mild. The AAFA’s 2025 Allergy Capitals research noted upward movement for several California cities, attributed to grass and weed pollen after wet weather.
November falls between the main chapters of the California pollen year — the tail of one and the approach of the next — so the calendar alone explains little today, and the modelled split above carries the story. Between them, the three chapters cover 9 months of the California year, February to October — leaving a quiet gap of roughly 3 months in the depth of the off-season. The full calendar is set out in the California allergy season guide.
How to read this index
Pollen Atlas reports the Castro Valley pollen count on a Total Pollen Index from 0 to 100, built from separate tree, grass and weed readings. The total is a summary, not an average of the three: a single strong category can lift it, and three quiet categories can hold it down even in a month when Castro Valley, CA pollen is usually more active. Index values are a modelled pollen risk index computed by Pollen Atlas from open weather, vegetation and phenology data, calibrated against CDC/NAB season data, with plant detail by the Google Pollen API. The index is a modelled 0–100 scale, not a measured count, and figures update through the day, so a morning and an evening visit to this page can legitimately show different numbers.
Castro Valley in today’s national picture
At 25 (Low), Castro Valley ranks joint 36055th of the 90896 cities Pollen Atlas tracks today — in the middle of the national table. The highest reading in the country today is Serpa, Portugal at 53, and the lowest is Galiakberovo, Russia at 5. The whole table spans 48 points today — a wide-open day, when the top and bottom of the table are effectively in different seasons.
Around Castro Valley: Fairview, CA (2 miles away) reads 22 (Low); Cherryland, CA (3 miles away) reads 25 (Low); Ashland, CA (3 miles away) reads 25 (Low). Castro Valley reads 3 points higher than its nearest tracked neighbour today. Across California’s 1602 tracked cities, today runs from 5 in Truckee to 42 in Mecca.
Pollen totals are population numbers; symptoms are personal. The same reading can leave one Castro Valley resident untouched and floor another, depending on which pollens they are sensitised to. If this pattern finds you every season, allergists in Castro Valley, CA can test whether tree, grass, weed or mold is the category that matters for you — the four readings at the top of this page are the starting point for that conversation.
Castro Valley in its local area
Castro Valley is a census-designated place in Alameda County, California. Its population is 65,389 (ACS 2023).
Across California’s 1602 tracked cities, Castro Valley ranks joint 415th today.
Like every Pollen Atlas city page, the Castro Valley, CA pollen count is refreshed each morning.
Nearby cities
- Fairview pollen count (2 miles away)
- Cherryland pollen count (3 miles away)
- Ashland pollen count (3 miles away)
- San Lorenzo pollen count (5 miles away)
- Norris Canyon pollen count (5 miles away)
- San Leandro pollen count (5 miles away)
From Pollen Atlas News
See how Castro Valley ranks in today's pollen count rankings — the worst cities for allergies today
See Castro Valley on the US pollen map
Pollen indexes: a modelled pollen risk index computed by Pollen Atlas from open weather, vegetation and phenology data, calibrated against CDC/NAB season data. Plant detail: Google Pollen API. Index values are modelled, not measured counts. Sources: CDC/NAB; USA-NPN; GBIF (CC BY); ESA WorldCover (CC BY 4.0).