Weed Pollen Builds Across Wisconsin and the Interior West, with Cincinnati Grass Newly High

Weed pollen is the clearest late-summer burden for allergy sufferers. Wisconsin carried the broadest high-pressure cluster, with Greenfield, La Crosse, and Madison all reaching the high range. In the West, Reno also moved into high weed levels, while Colorado Springs and Riverton stayed active at moderate levels. Moderate weed pockets also appeared in the Midwest, South Central region, and parts of the Southeast, showing that the season is building unevenly rather than arriving everywhere at once.

Grass was less widespread at high levels, but Cincinnati stood out after rising from moderate to high. Nashville remained moderate, and South Central grass stayed active but below high levels around Oklahoma City, Tulsa, and Waco. Colorado Springs was the main moderate Western grass location. Elsewhere, grass readings were mostly low or absent from the higher ranges.

Mold remained local but important. Chicago stayed high, driven by ascospores, while St. Louis slipped from last week's top severity band into moderate territory. Houston and Washington also reached moderate mold levels, but most other available stations were low.

Tree pollen looked late-season and limited. Mainland tree readings were mostly low, with Waco moderate elm reading the main exception. Puerto Rico also moved below the high range, with San Juan dropping to moderate and Caguas staying low.

High Allergy Burden Locations

Pollen Drivers

Weed pollen had the most meaningful species detail. Nettle-family pollen drove the high weed readings in La Crosse and Madison, while sheep sorrel and dock drove Greenfield. Ragweed was not a high driver, but it appeared at moderate levels in parts of the Midwest and at Rochester, showing early-season activity in places that have not yet reached the higher bands.

In the West, Reno's high weed reading came from the goosefoot, lamb's quarters, pigweed, amaranth, saltbush, and Russian thistle group. That same group also showed up at moderate levels in Colorado Springs, Riverton, Omaha, and Oklahoma City, making it one of the more repeated late-summer weed drivers outside Wisconsin.

Mold was led by ascospores, which drove Chicago's high reading and showed up at moderate levels in St. Louis, Houston, and Washington Silver Spring. Tree pollen had few notable drivers: elm was moderate at Waco Woodway South, and Puerto Rico's remaining moderate tree reading was reported as other identified tree pollen.

Weather Context

The Midwest turned warmer and wetter, with slightly stronger winds than last week. That coincided with Wisconsin weed readings holding or moving into the high range and with Chicago mold remaining elevated, even as St. Louis mold fell back from last week's top severity band.

The West cooled but picked up more rain overall. Reno's weed rise and Colorado Springs' step down from high to moderate made the regional weed pattern mixed, while Western grass stayed below high levels.

The Southeast became warmer and less rainy after a wetter stretch, which coincided with Cincinnati Florence grass rising into the high range and Nashville staying moderate for grass and weeds. South Central weather stayed hot and relatively dry, matching a pattern of moderate grass, mold, and weed pockets without any high readings.

The Northeast had less rain and similar temperatures, but available readings stayed low outside Rochester's moderate ragweed. Puerto Rico remained warm with somewhat more rain, while tree and grass readings stayed below high levels at available stations.