Synoptic-Scale Environments of Predecessor Rain Events Occurring East of the Rocky Mountains in Association with Atlantic Basin Tropical Cyclones*

Abstract

The synoptic-scale environments of predecessor rain events (PREs) occurring to the east of the Rocky Mountains in association with Atlantic basin tropical cyclones (TCs) are examined. PREs that occurred during 1988-2010 are subjectively classified based upon the synoptic-scale upper-level flow configuration within which the PRE develops, with a focus on the following: 1) the position of the jet streak relative to the TC, 2) the position of the jet streak relative to trough and ridge axes, and 3) the positions of trough and ridge axes relative to the PRE and to the TC. Three categories were identified from this classification procedure: ''jet in ridge,'' ''southwesterly jet,'' and ''downstream confluence.'' PRE-relative composite analysis for each category reveals that, consistent with previous studies, PREs typically occur near a low-level baroclinic zone, beneath the equatorward entrance region of an upper-level jet streak, and in the presence of a stream of water vapor from a TC. Despite these common characteristics, key differences exist among the three PRE categories related to the phasing of a TC with the synoptic-scale flow and to the interactions between a TC and its environment. Brief case studies of PREs associated with TC Rita (2005), TC Wilma (2005), and TC Ernesto (2006) are presented as specific examples of the three PRE categories.

The Key Role of Diabatic Outflow in Amplifying the Midlatitude Flow: A Representative Case Study of Weather Systems Surrounding Western North Pacific Extratropical Transition

“…When this moisture impinges on a midlatitude baroclinic zone in a region of upperlevel forcing for ascent [e.g., near the equatorward entrance region of an upper-level jet streak; Uccellini and Johnson (1979)] several days prior to ET, heavy precipitation and flooding may occur as a result of quasistationary convection in that region (e.g., Wang et al 2009;Galarneau et al 2010;Byun and Lee 2012;Schumacher and Galarneau 2012;Baek et al 2013). The associated weather system, called a predecessor rain event (PRE; e.g., Galarneau et al 2010;Bosart et al 2012;Moore et al 2013), tends to be located 500-2000 km away from the TC. Because of the strong latent heat release, a PRE likewise exhibits intense diabatic outflow.…”

“…The divergent outflow and initial ridge building results from the diabatically driven strong ascent and associated latent heat release in the TC inner core and later at the midlatitude baroclinic zone yielding a net transport of lower-tropospheric air with low values of potential vorticity (PV) to the tropopause (e.g., DiMego and Bosart 1982;Bosart and Lackmann 1995;Torn 2010;Grams et al 2013b). Also, other weather systems such as predecessor rain events (PREs; Galarneau et al 2010;Moore et al 2013) and warm conveyor belts (WCBs; e.g., Carlson 1980;Madonna et al 2014b) occur surrounding an ET event, exhibit strong diabatic outflow, and may modify the upper-level Rossby wave pattern in a similar manner as the actual ET (Ahmadi-Givi et al 2004;Grams et al 2011;Bosart et al 2012;Lang and Martin 2013;Moore et al 2013;Madonna et al 2014a;Galarneau 2015;Teubler and Riemer 2016). The diabatic nature of this interaction alters the behavior of Rossby waves expected from a purely dry dynamical perspective.…”

A Composite Perspective of the Extratropical Flow Response to Recurving Western North Pacific Tropical Cyclones

“…Although this study did not directly address predictability, it provides a potential framework in which to evaluate numerical model forecast error and uncertainty associated with the TC-extratropical flow interaction for recurving TC cases and other weather phenomena associated with divergent outflow that may impinge strongly upon the PV waveguide [e.g., predecessor rain events (Bosart et al 2012;Moore et al 2013) and atmospheric rivers ]. Many studies suggest that large numerical model forecast errors may result from a failure of the numerical model to adequately capture diabatically driven ridge amplification (e.g., Davies and Didone 2013;Gray et al 2014), whether associated with recurving TCs (e.g., Henderson et al 1999;Torn 2010), mesoscale convective systems (e.g., Dickinson et al 1997;Rodwell et al 2013), or warm conveyor belts of explosively deepening extratropical cyclones (e.g., Doyle et al 2014).…”

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.…”