THE GREAT-PLAINS LOW-LEVEL JET DURING THE WARM-SEASON OF 1993

Hourly wind profiler observations from the NOAA Profiler Network were used to develop a climatology of the low-level jet (LLJ) over the Grea t Plains of the central United States from April to September of 1993. The peak precipitation episode of the 1993 flood was associated with a sustained period of high incidence of strong low-level jets (over 20 m s(-1)). Consistent with previous studies, strong low-level jets wer e found to be promoted in the warm sector of an extratropical cyclone. Comparison of datasets formulated using velocity variance thresholds with unthresholded data similar to the operational hourly data suggest s that the profiler observations often were contaminated by radar retu rns from migrating birds, especially during the months of April and Ma y. The strong low-level jets during the peak precipitation episode of the 1993 hood over the upper Mississippi River basin were associated w ith a high-amplitude upper-level wave pattern over and upstream of the continental United States. Separating the composite 850-mb wind for s trong low-level jets into geostrophic and ageostrophic components show ed that the magnitudes of the ageostrophic component and the anomalous geostrophic component were comparable.