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Grass Pollen Keeps Midwest and Western Allergy Pressure High as South Central Mold Rises

May 30, 2026 by PollenScience Staff

Eugene remained the sharpest grass location, while Wisconsin, Chicago, Portland, Seattle, Puerto Rico, and parts of Oklahoma and Texas stayed active. Tree pollen is now more concentrated in northern locations, while weeds are still mostly quiet.

National Overview

Grass pollen is the main burden for many allergy sufferers. The Midwest and West carried the broadest pressure, with high grass readings clustered around Chicago and Wisconsin in the Midwest and Eugene, Portland, and Seattle in the Pacific Northwest. Eugene remained the only grass location in the top severity band, while Puerto Rico stayed active in both San Juan and Caguas.

South Central grass pollen remained elevated in Oklahoma City and Waco, but the region's more notable change was mold. San Antonio reached Very High for mold, while Austin and Oklahoma City both moved into high mold territory. That pattern coincided with another warm, wet stretch across Texas and Oklahoma.

Tree pollen has started to wane in intensity in the South as that part of the seasonal allergy season begins to lessen. The Southeast and South Central stations were below high tree levels, while the remaining tree burden sat farther north. Alaska stayed active for birch, Reno moved up for pine-family pollen, Armonk and Olean kept New York tree readings elevated, and both Puerto Rico stations remained high.

Weeds were mostly quiet. Madison was the only high weed location, driven by nettle-family pollen; elsewhere, weed readings were low to moderate.

High Allergy Burden Locations

Location Allergen Level Drivers
Eugene, OR Grass Very High Grass Family, all types
San Antonio (East), TX Mold Very High Other identified fungi
Anchorage (South), AK Tree High Birch
Armonk, NY Tree High Hickory, Pecan; Pine Family with air bladders
Austin (Georgetown), TX Mold High Other identified fungi
Caguas (Centro), PR Grass High Other identified grass pollen
Caguas (Centro), PR Tree High Other identified tree pollen
Chicago (Melrose Park), IL Grass High Grass Family, all types
Fairbanks, AK Tree High Birch
Greenfield, WI Grass High Grass Family, all types
Greenfield, WI Tree High Birch; Mulberry; Oak
La Crosse (Onalaska), WI Grass High Grass Family, all types
Madison, WI Grass High Grass Family, all types
Madison, WI Tree High Pine Family with air bladders; Walnut, Butternut
Madison, WI Weed High Nettle family, Pellitory
Oklahoma City, OK Grass High Grass Family, all types
Oklahoma City, OK Mold High Ascospores; Cladosporium
Olean, NY Grass High Other identified grass pollen
Olean, NY Tree High Oak
Portland, OR Grass High Grass Family, all types
Reno (Sparks), NV Tree High Pine Family with air bladders
San Juan, PR Grass High Grass Family, all types
San Juan, PR Tree High Other identified tree pollen
Seattle, WA Grass High Grass Family, all types
Waco (Woodway South), TX Grass High Grass Family, all types
Washington (Silver Spring), MD Grass High Grass Family, all types

Pollen Drivers

For trees, birch was the clearest named driver in Alaska and also contributed in Greenfield. Pine-family pollen showed up in Madison, Armonk, and Reno, while oak was the named tree driver in Olean. Puerto Rico's elevated tree readings came through the broad tree category rather than a named species.

Mold was concentrated in the South Central region. San Antonio and Austin were led by other identified fungi, while Oklahoma City had both ascospores and Cladosporium in the high range. Weed pollen had little reach beyond Madison, where nettle-family pollen accounted for the elevated reading.

Weather Context

Warmer Midwest weather coincided with the renewed grass activity in Wisconsin, Chicago, and La Crosse after a wetter, windier prior stretch. The South Central region stayed warm and wet, which coincided with the rise in mold around San Antonio, Austin, and Oklahoma City.

The Southeast turned wetter while tree pollen stayed below high levels and grass was limited mainly to Washington, DC. The Northeast was cooler and much wetter, but New York still had elevated tree readings at Armonk and Olean. The West was mild with modest precipitation, while Pacific Northwest grass stayed active and Alaska birch continued to matter.

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