15.4
A potential vorticity streamer and its role in the development of a week-long series of mesoscale convective systems, part II: mesoanalysis of a prominent storm in the series
Fernando Caracena, NOAA/ERL/FSL, Boulder, CO; and A. Marroquin and E. I. Tollerud
An elongated, narrow band of potential vorticity (PV-streamer) spawned a succession of convective systems occurring the week following 27 June 1999. The PV-streamer was associated with a narrow jet streak that emerged from a sheared-off easterly wave in the tropical, eastern Pacific. Not only did severe storms associated with this PV-streamer produce tornadoes hail and wind damage, but the storms deposited an impressive amount of precipitation over Kansas, Oklahoma, Arkansas, and neighboring states. Here we focus on the first storm in the series which occurred the night of 27-28 June. It began as a large supercell storm in Wyoming, propagated across northeast Colorado into Nebraska and Kansas. During the night it grew into a Mesoscale Convective System (MCS) reaching the size and shape of a Mesoscale Convective Complex by 1200 UTC 28 June 1999 over eastern Kansas and western Missouri. As the PV-streamer first emerged onto the Plains over the central Rocky Mountains late on 27 June, it enhanced lee cyclogenesis and a low-level jet that directed pre-frontal air containing high values of convective potential energy over an old frontal boundary. A supercell thunderstorm forming in the path of the PV-streamer quickly grew and became organized into an MCS. Results of diagnostic computations using RUC-2 and Eta model initial fields indicate that PV from the nose of the PV-streamer became connected with mid- and low-level PV either convected and/or generated by deep moist convection, forming a column of PV that was situated in a dry-slot of a comma shaped radar echo, between the anvil precipitation area and an imbedded squall line. A fairly large number of sounding, profiler and ACARS observations allow a critical analysis of model initial fields. In addition to the above diagnostic work, results of simulations will be presented regarding the dynamics of the PV streamers in relation to the growth and development of MCSs using high-resolution (10 km horizontal resolution), nonhydrostatic numerical models such as the Regional Atmospheric Modeling System (RAMS) and the Mesoscale Model version 5 (MM5) from the Pennsylvania State University - National Center for Atmospheric Research (NCAR).
Session 15, Mesoscale And Synoptic-Scale Processes And Severe Convection I
Friday, 15 September 2000, 1:30 PM-3:00 PM
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