Although prevalent weather helps define climate, individual weather conditions, such as rain, humidity, wind speed and direction, temperature, or amount of sunshine, may have direct and indirect effects on bioaerosols. Effects may be immediate or cumulative. Precipitation and humidity acutely decrease particle air burden, but sufficient preseason moisture is necessary to assure proper growth of flower buds on perennials and trees and growth of annuals in general. Ambient temperature increase is necessary for anthesis in many plants, and cumulative heat above a threshold value has been linked to onset and intensity of pollination in grasses, weeds, and trees. Wind direction only impacts if there is lack of uniformity in the pollen sources that surround sampling sites. Wind speed may factor in re-entrainment of settled particles or may act to scour the air. Thunderstorms provide a unique sum of factors that greatly may increase aeroallergen burden. Dispersal of mold spores is linked intimately to precipitation and humidity. The effects may be opposed diametrically, however, depending on the type of fungi. Certain ascospores and basidiospores require active rainfall for release of spores, whereas other Deuteromycetes are suppressed by precipitation.