Pollen Today for San Mateo, CA
Low pollen in San Mateo, CA today
Tree: Low · Grass: Low · Weed: Low
Tree pollenLow (UPI 0/5)
UPI is the Universal Pollen Index, a 0–5 scale (0 none, 5 very high) that is comparable across pollen types and locations.
- Grass pollenLow (UPI 0/5)
- Weed pollenLow (UPI 0/5)
- TimingCounts peak 10am–3pm; lowest overnight and after rain
- TipGood day for outdoor activities
Data as of Oct 18, 2026
Coming Up
Pollen season outlook for San Mateo
The pollen model for San Mateo shows no plant species actively releasing pollen right now — a break for allergy sufferers.
Ragweed is the driver this time of year, and in San Mateo it has roughly 69 days left to run. Weed pollen doesn't stop on a calendar date — it stops when a hard frost kills the plants, and San Mateo's average first frost falls around December 26.
That is why the same ragweed season is weeks shorter in the northern states than in the South: identical plants, different frost dates. A single ragweed plant can release around a billion pollen grains, and they travel hundreds of miles on the wind, so a low local count doesn't guarantee a quiet day.
Worth having
Affiliate disclosure: we may earn a commission if you buy through these links, at no extra cost to you. We only list things we’d recommend anyway.