Monday, 17 August 2009: 9:45 AM
The Canyons (Sheraton Salt Lake City Hotel)
This study examines a winter-storm event in Oklahoma that occurred from 29 Nov. to 01 Dec. 2006. During this event, mesoscale and convective-scale observations were acquired from the CASA network of low-powered, polarimetric, high-resolution X-band radars, the WSR-88D network, the dual-polarized testbed WSR-88D radar, KOUN, the Oklahoma Mesonet, and the National Weather Service upper-air network. This event provided a unique opportunity to observe the entire breadth of precipitation associated with a midlatitude cyclone, and is broken down into four phases according to the characteristics of the precipitation and where the precipitation fell relative to the parent cyclone. Within each phase, unique small-scale precipitation structures were observed including a narrow cold-frontal rainband, single-cell and multicellular convective elements, a post-frontal rainband, and bands embedded within stratiform regions. Wave-like features, hypothesized to be Kelvin-Helmholtz waves, occurred intermittently during the middle stage of the storm and were apparent in reflectivity, radial velocity, spectrum width, and several polarimetric fields. Horizontal convective rolls were manifest in the radial velocity data throughout most of the storm.
The forcing mechanisms, local environments and dynamical processes involved with these features are examined. It is determined that during the first half of the event, conditional symmetric instability may have played a minor role in certain banding occurrences, but elevated gravitational instability dominated in environments near embedded bands. Gravity-wave signatures are apparent in surface meteograms, and were likely a result of nearby convection rather than a cause of the convection. Kelvin-Helmholtz waves are hypothesized to be a result of dynamic instability along a shear interface separating cold and warm air. Horizontal convective rolls also are determined to be a result of dynamic shear instability.
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