Summer Surface Flow Characteristics over Northeast Colorado

James J. Toth Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523

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Richard H. Johnson Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523

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Abstract

Surface wind data from the program for Regional Observing and Forecasting Services (PROFS) have been analyzed to investigate the diurnal wind flow pattern over the broad drainage are of the South Platte River in northeast Colorado. A consistent diurnal pattern appears in monthly averages as well as on most undisturbed individual days, and is similar to the classic descriptions of mountain-valley wind flows. It is observed that rather than occurring simultaneously at all elevations, downslope-to-upslope and upslope-to-downslope surface flow transitions along the Front Range of northeast Colorado begin near the foothills of the Rocky Mountains and propagate eastward across the plains.

During the summer months, local confluence is found at midday along major east-west ridges in the region (e.g., Cheyenne Ridge and Palmer Lake Divide). Consequently, in addition to the north–south Continental Divide, these east–west ridges are preferred regions for initial afternoon thunderstorm development The late afternoon transition to downslope flow often appears to be associated with the propagation of thunderstorms from the mountains and ridges eastward to the plains.

Abstract

Surface wind data from the program for Regional Observing and Forecasting Services (PROFS) have been analyzed to investigate the diurnal wind flow pattern over the broad drainage are of the South Platte River in northeast Colorado. A consistent diurnal pattern appears in monthly averages as well as on most undisturbed individual days, and is similar to the classic descriptions of mountain-valley wind flows. It is observed that rather than occurring simultaneously at all elevations, downslope-to-upslope and upslope-to-downslope surface flow transitions along the Front Range of northeast Colorado begin near the foothills of the Rocky Mountains and propagate eastward across the plains.

During the summer months, local confluence is found at midday along major east-west ridges in the region (e.g., Cheyenne Ridge and Palmer Lake Divide). Consequently, in addition to the north–south Continental Divide, these east–west ridges are preferred regions for initial afternoon thunderstorm development The late afternoon transition to downslope flow often appears to be associated with the propagation of thunderstorms from the mountains and ridges eastward to the plains.

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