Pollen Count & Forecast for Portland

Portland’s spring allergy season (February–May) is dominated by Alder and Fir pollen; Red Alder (Alnus rubra) prolific along the Willamette River and in Forest Park; Douglas Fir (Pseudotsuga menziesii) widespread across the West Hills and Mt. Tabor Park. Oak (Quercus) contributes from Washington Park. Summer (May–July) sees high Grass (Poaceae) pollen levels, originating from the Willamette Valley south of the city.

The Tualatin Mountains and urban hills trap pollen in the city basin; Columbia River Gorge winds carry spores into eastern neighborhoods. Autumn and winter see high Mould (Alternaria, Cladosporium) counts, from decomposing leaf litter in damp parks and wet urban environments.