THE SUMMERTIME GREAT-PLAINS LOW-LEVEL JET AND THE EFFECT OF ITS ORIGIN ON MOISTURE TRANSPORT

Radiosonde data from six stations in Kansas and Oklahoma for the perio d of June 16-24, 1993 indicate that a low-level jet (LLJ) occurred alm ost every day except on the 20th. Major characteristics of these LLJs are documented in this paper. The maximum wind speed (the jet speed) v aried from 13 to 32 m s(-1) and heights ranged from 167 to 910 m. All the jets were southerly except the one on June 19 which changed its di rection dramatically from a southerly to a northerly direction in abou t three hours although its intensity did not change appreciably. Therm al stability of the boundary layer during these LLJ occurrences ranged from near-neutral to highly stable. All the low-level jets exhibited significant diurnal variations. Analyses show that relatively weak lar gescale forcing existed for the LLJs on June 21 and June 22, while str ong forcing was present on other days. Analyses also show that moistur e transport by the LLJ from the Gulf of Mexico to the Great Plains dep ends on the location of the LLJ origin. In the two weeks of June 13-19 and 20-26, 1993, powerful storms swept through the central United Sta tes, accompanied by tornadoes, strong wind, large hail and heavy rainf all. The analyses indicate that these weather events could be a result of the interactions of the LLJs with synoptic-scale flow.