An Analysis of a Shallow Cold Front and Wave Interactions from the PLOWS Field Campaign

This paper presents an analysis of a shallow cold front and its impact on precipitation within a weak cyclone over southern Indiana, observed during The Profiling of Winter Storms (PLOWS) field campaign on 14-15 February 2010 (IOP-19). During this event a shallow surface cold front was sampled by three PLOWS mobile platforms, including the NCAR Mobile Integrated Sounding System (MISS; 915 MHz wind profiler and soundings), the Mobile Alabama X-band (MAX) dual polarization radar (including surface measurements), and the UAH Mobile Integrated Profiling System (MIPS; 915 MHz wind profiler, X-band profiling radar, microwave profiling radiometer, ceilometer, surface instrumentation, and Parsivel disdrometer). These three platforms were set up along a line oriented from 250 to 70 deg, with separation distances of 47 and 15 km, respectively. In addition, the Evansville WSR-88D radar (KVWX) and surface stations (including AWOS and co-op stations) were used in the analysis of cold frontal characteristics.

The shallow font moved over the linear array of instrumentation between 0300 and 0600 UTC. Wind profiles were available from the MISS and MIPS 915 MHz wind profilers and from EVAD analyses performed on the KVWX and MAX radar data. The front exhibited a sharp wind shift, 6-8 °C temperature reduction, shallow depth (< 1km), and significant pressure rise (1.5 hPa). Wave-like features were notable above the front as it moved over the MAX radar. The shallow cold front was followed by a deeper, but less distinct cold front which passed through the IOP-19 domain 9 hours after the initial front. Both fronts were well sampled by the KVWX, MISS 915 MHz wind profiler, MAX VAD and RHI, and MIPS 915 MHz wind profiler, XPR, and MPR. A two dimensional single Doppler analysis was performed using RHIs from MAX to derive detailed, high resolution front relative flow around the shallow cold front and associated waves. A prefrontal sounding from the MISS location revealed a stable layer with lapse rates 4-5 °C /km over the depth of the front. This stable layer supported wave features and distinct perturbations in XPR reflectivity and vertical particle velocity. The impact of the cold front and associated waves on surrounding precipitation is assessed with the combined profiler, 2-D Doppler analysis, and MAX dual polarization data.