Multiscale Structure and Evolution of an Oklahoma Winter Precipitation Event

Abstract

A significant winter precipitation event occurred on 8-9 March 1994 in Oklahoma. Snow accumulations greater than 30 cm (12 in.) were measured within a narrow corridor in northern Oklahoma. On the synoptic scale and mesoscale, a correspondence between large snow accumulations and 600-hPa frontogenesis was revealed; the precipitation was formed above the cold frontal surface, owing to midtropospheric ascent associated with the cross-frontal circulation in a region of elevated conditional instability. The location of such a narrow corridor of large accumulations was not, however, disclosed by any patterns in the radar reflectivity data. Indeed, during this event, an elongated maximum of snow accumulation was not associated with a persistent ''band'' of enhanced reflectivity and vice versa. Dual-polarization and dual-Doppler radar data allowed for a novel analysis of winter precipitation processes and structures, within the context of the larger-scale diagnosis. It was possible to identify, in order of distance southward toward the surface cold front: (i) an elevated convective element, which was classified as an elevated thunderstorm and may have functioned as an ice crystal ''generator'' cell, embedded within a broad region of generally stratiform precipitation; (ii) a reflectivity band and associated rain-snow transition zone, the evolution and structure of which apparently were coupled to the effects of melting precipitation and strong vertical wind shear; and (iii) a mixed-phase precipitation-generating, prolific lightning-producing, nonelevated thunderstorm cell that was sustained in the postfrontal air in part by virtue of its rotational dynamics.

A Dual-Polarization Radar Hydrometeor Classification Algorithm for Winter Precipitation

“…However, they also have the highest Z h compared to plates, dendrites, or any other ice crystals because of their larger diameters (Ohtake and Henmi 1970;Ryzhkov and Zrni c 1998;Boucher and Wieler 1985). Trapp et al (2001) and Ryzhkov et al (2005b) propose that Z dr tends to decrease as Z h increases, or as aggregation progresses, density decreases, and fall behavior becomes more erratic. Our simulations also suggest a minimum reflectivity value associated with aggregates near 20 dBZ, which is used to differentiate aggregates from individual, nonoriented, small ice crystals in section 4.…”

“…Terms K dp and Z dr are the most important and heavily weighted variables for distinguishing dendrites, plates, and aggregates, since r hy and Z h are usually innocuous (Trapp et al 2001). However, Z h was weighted highest FIG.…”

Using Frontogenesis to Identify Sting Jets in Extratropical Cyclones

“…Petterssen frontogenesis has been used previously to diagnose fronts in the central United States (e.g., Koch 1984;Keshishian et al 1994;Martin 1998a;Schultz 2004), the western United States (Steenburgh and Mass 1994;Schultz and Knox 2007;Steenburgh et al 2009;Schumacher et al 2010;West and Steenburgh 2010), and idealized baroclinic waves (Sch€ ar and Wernli 1993;Schultz and Zhang 2007); to calculate climatologies of frontogenesis (Satyamurty and De Mattos 1989); to determine regions of ascent associated with precipitation bands within heavy rainstorms (Sanders 2000) and within snowstorms (e.g., Bosart and Lin 1984;Keshishian and Bosart 1987;Roebber et al 1994;Martin 1998b;Trapp et al 2001;Novak et al 2004Novak et al , 2006Novak et al , 2008Novak et al , 2009Novak et al , 2010; to determine the time of extratropical transition of a tropical cyclone (Harr and Elsberry 2000); and to indicate regions of predecessor precipitation ahead of tropical cyclones (e.g., Galarneau et al 2010;Moore et al 2013). Lackmann (2011, sections 6.2 and 6.3) provides a moredetailed description of Petterssen frontogenesis.…”

Elevated Convection and Castellanus: Ambiguities, Significance, and Questions

“…As previously noted, such convection is of considerable interest given its potential to produce severe weather, even well within the cold air (e.g., Neiman et al 1993;Grant 1995;Trapp et al 2001;Horgan et al 2007). Figure 2c shows elevated thunderstorms forming about 150 km north of a slowly moving warm front.…”