Hollister, Idaho

Pollen is rated on the National Allergy Bureau bands for the grains of pollen in a cubic meter of air. Trees: Low under 15, Moderate 15 to 89, High 90 to 1,499. Weeds: Low under 10, Moderate 10 to 49, High 50 to 499. Grass: Low under 5, Moderate 5 to 19, High 20 to 199. The band is the one reached on the busiest quarter of counted days. A rating is typical, not a forecast: one wet or windy year can move it.

Spring trees, Moderate. Twin Falls NAB station, 757 counted days in 2003 to 2024: on the busiest quarter of days the tree count was 54 grains per cubic meter or more, which the NAB bands call Moderate. On the busiest tenth of days it was 125 or more.

Early-summer grass, High. No grass counts are published for Twin Falls. The Treasure Valley figure is used: the same Snake River Plain, and Twin Falls tree and weed counts match Boise's pattern. The NAB grass bands: Low under 5, Moderate 5 to 19, High 20 to 199, Very High 200 or more grains per cubic meter.

Fall weeds and sagebrush, High. Twin Falls NAB station, 536 counted days in 2004 to 2023: on the busiest quarter of days the weed count was 71 grains per cubic meter or more, which the NAB bands call High. On the busiest tenth of days it was 114 or more.

Wildfire smoke, Moderate. The average number of days a year the EPA's air quality index passed 100 ("unhealthy for sensitive groups" or worse), 2021-2025. Under 3 days is Low, 3 to 9 Moderate, 10 or more High. That grouping is ours, not the EPA's. Twin Falls County has its own EPA air monitor. The count includes any cause, but across Idaho's monitors 86% of those days fell in July to September and 94% were fine particles (PM2.5), which is what wildfire smoke is made of (570 county-days, 2021-2025).

Not rated. Mold: no published mold spore counts for Idaho towns are in the data used, so there is no mold rating. House dust, pets and food allergies are outside this rating.