Derecho and MCS Development, Evolution, and Multiscale Interactions during 3–5 July 2003

Abstract

From 3 to 5 July 2003 during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX), multiple mesoscale convective systems (MCSs 1 and 2) and derechos (derechos AN, AS, A, BW, and BE) progressed across a preferred upper Midwest corridor. The derechos evolved in a favorable synoptic-scale environment. However, the environmental details associated with each derecho, such as the characteristics of the initial surface boundary, the formation position relative to the upper-level jet stream, the presence of an upper-level mesoscale disturbance, and the CAPE/shear environment varied from derecho to derecho. The MCSs and derechos composed three distinct convective episodes. Multiple mesoscale interactions between the MCSs and derechos and the environment altered the character and longevity of these episodes. The first convective episode consisted of derecho A, which formed from merging derechos AN and AS (northern and southern systems, respectively). The ∼200-hPa-deep cold pool associated with derecho A decreased surface potential temperatures by 4–8 K. MCS 1 dissipated upon entering this cold pool and an inertia–gravity wave was emitted that helped to spawn MCS 2. This inertia–gravity wave connected MCSs 1 and 2 into a compound convective episode. As derecho BW (western system) approached a strong surface boundary across Iowa created by the cold pools of derecho A and MCS 1, derecho BE (eastern system) formed. The remnants of derecho BW merged with derecho BE creating another compound convective episode. The upscale effects resulting from this active convective period directly affected subsequent convective development. Upper-level diabatic heating associated with derecho A resulted in NCEP GFS 66-h negative 1000–500-hPa thickness errors of 4–8 dam (forecast too cold) and negative 200-hPa wind errors of 10–20 m s−1 (forecast too weak). The resulting stronger than forecast 200-hPa jet stream likely increased synoptic-scale forcing for the formation and evolution of derecho BW.

An Analysis of Multiple Predecessor Rain Events ahead of Tropical Cyclones Ike and Lowell: 10–15 September 2008

“…The observed diabatic influence of the PREs on downstream ridge amplification is comparable to the synoptic-scale feedback from diabatic heating associated with heavy precipitation accompanying tropical convection (e.g., Sardeshmukh and Hoskins 1988), MCSs (e.g. ; Fritsch and Maddox 1981;Chen et al 2006;Saulo et al 2007;Metz and Bosart 2010), recurving and transitioning TCs (e.g., Bosart and Lackmann 1995;Atallah and Bosart 2003;Riemer et al 2008;Torn and Hakim 2009;Archambault 2010;Riemer and Jones 2010), extratropical cyclones (e.g., Dickinson et al 1997;Bosart 1999;Pomroy and Thorpe 2000;Archambault et al 2010), and positively tilted PV streamers (e.g., Massacand et al 2001).…”

Central and Eastern U.S. Surface Pressure Variations Derived from the USArray Network

“…The overlapping temporal scales within which these pressure perturbations and associated phenomena occur include the following: d Less than 20 min: high-frequency internal gravity waves resulting from shear layers, horizontal convective rolls, katabatic flows, and other boundary layer phenomena (Tian et al 2004; Adams-Selin and Johnson 2010; Viana et al 2010); d 5 min-4 h: propagating gravity waves associated with individual convective storms and associated cold pools, mesohighs and wake lows, bow echoes, derechos, and other mesoscale disturbances (Crook 1988;Engerer et al 2008;Metz and Bosart 2010); d 2-12 h: differential heating of land and water surfaces (Novak and Colle 2006), elevated terrain (Geerts et al 2008), long-lived mesoscale gravity waves and inertiagravity waves, cold fronts, or drylines associated with large synoptic disturbances (Jewett et al 2003;Bosart et al 1998), or prolonged flow over a topographic barrier (Gaber sek and Durran 2006); and d 12-24 h: diurnal and semidiurnal migrating thermal tides due to diurnal heating (Dai and Wang 1999;Li and Smith 2010).…”

A Case Study of Atmospheric Dynamics and Thermodynamics in Derechos and the Societal Impacts

“…In addition, derechos form in very unstable environments indicated by high values of Convective Available Potential Energy (CAPE) greater than 1500 J Kg -1 . On the other hand, they have been shown to form in low CAPE environments (less than 500 J kg -1 ) if the synoptic forcing is high [21,22]. The objective of this study is to investigate the dynamic and thermodynamic factors responsible for the 2012 outbreak and determine if those parameters during the event were signifi-cantly different from the mean values.…”