Starting in the 1980s the long distance transport of Juniperus ashei (mountain cedar) pollen from populations in southern Oklahoma and Texas has been recorded. Pollen from this species is highly allergenic and affects a significant percent of allergy patients in central Texas and other areas of the southern plains. The mountain cedar system is unique because pollination occurs in December and January, a time distinct from other plants, including other species of Juniperus. Pollen from this species is registered in our air samplers in Tulsa on 30% to 40% of the days in December and January. Starting in Dec 1998 mountain cedar pollen forecasting has been undertaken to warn downwind populations of the potential threat of high pollen concentrations in the atmosphere. The downwind forecast is based on trajectories generated using the HY-SPLIT dispersion model from NOAA Air Resources. Based on air sampling in Oklahoma, our forecasts have accurately predicted most pollen incursions. Initially, it was believed that the transport was only regional carrying pollen into the Tulsa area from southern Oklahoma and Texas. However, when our trajectories were compared to data from other pollen sampling stations in the National Allergy Bureau, evidence of transport over greater distances is clear. In fact, during the six years of forecasting, Juniperus ashei pollen was registered over 20 times in London, Ontario.
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