Extended Abstract (28K)5.4
Analysis of an Orographically Modified Cyclone over the Western United States during IPEX IOP3
Jason C. Shafer, NOAA/CIRP and Univ. of Utah, Salt Lake City, UT; and W. J. Steenburgh and J. A. W. Cox
This paper describes the synoptic and mesoscale structure of a frontal cyclone that traversed the complex orography of the western United States during IOP-3 of the Intermountain Precipitation Experiment (IPEX). The analysis is based on conventional data, special radiosonde observations, high density surface observations collected by the MesoWest cooperative networks, NEXRAD radar data, wind profiler observations, and flight-level data from the NOAA P-3 aircraft.
It will be shown that as the mature cyclone and associated upper-level trough approached the US west coast, strong cross-barrier flow produced a stationary pressure trough to the lee of the Sierra Nevada. Concurrently, a mesoscale cyclonic vortex (MCV) developed over the relatively low elevations of northwest Nevada. This MCV developed in a region that was favorable for mid-tropospheric ascent, since strong differential cyclonic vorticity advection existed in the left exit region of an upper-level jet streak. As the upper-level trough and associated baroclinicity overtook the lee trough, the lee trough became mobile and the MCV dissipated. The surface pressure trough began to move downstream with the primary upper-level trough. Additionally, a discontinuous progression of the surface low pressure center and surface pressure trough axis was observed.
Prior to trough passage, strong south to southwesterly low-level flow was observed across Nevada and Utah. Flow channeling within the north-south oriented Salt Lake and Tooele Valleys of Northern Utah aided the development of windward confluence over the Great Salt Lake, and upstream of the Wasatch Mountains, where enhanced precipitation was observed. Terrain-driven confluence was also observed immediately north of the Stansbury Mountains where quasi-steady radar reflectivity returns were observed. Additional characteristics of the low-level flow over northern Utah will also be described, including a 12-15 m/s low-level wind maximum around 1km above ground level.
Supplementary URL: http://www.met.utah.edu/jimsteen/IPEX/
Session 5, Orographically Modified Cyclone Evolution
Tuesday, 18 June 2002, 8:00 AM-9:00 AM
Previous paper