High Winds Generated by Bow Echoes. Part I: Overview of the Omaha Bow Echo 5 July 2003 Storm during BAMEX

Abstract

An analysis of a bow echo that produced damaging winds exceeding F1 in intensity on the Fujita scale near Omaha, Nebraska, is shown. Part I of this study presents a combination of airborne Doppler-derived wind syntheses with a comprehensive damage survey in order to document the generation of strong winds at the surface. A detailed kinematic analysis of the evolution of a quasi-linear convective system into a bow-shaped and, subsequently, a spearhead echo is shown for the first time. It is hypothesized that a large, cyclonic bookend vortex (70–80 km in diameter) north of the bow apex enhanced the rear-inflow jet and initiated the “bowing process.” A hook-shaped echo and mesovortex formed at the apex of a bowed segment of the convective line and was located to the north of the swath of strong damage rated greater than F1 in damage intensity. The peak single-Doppler radial velocity recorded by the tail radar was 43 m s−1 in the low-level outflow near the apex of the bow echo. The regions of the strongest single-Doppler velocities at the lowest grid level were not always associated with the most intense damage at the surface. This discrepancy may be related to the development of a stable nocturnal boundary layer that prevented the strong outflow winds from reaching the surface. An intensifying rear-inflow jet was revealed in vertical cross sections through the bow echo. The relationship between mesovortices and strong surface winds is examined in Part II.

The Impact of Large-Scale Forcing on Skill of Simulated Convective Initiation and Upscale Evolution with Convection-Allowing Grid Spacings in the WRF*

“…Mesoscale convective systems produce a significant portion of warm-season rainfall (Fritsch et al 1986) and a large amount of severe weather (Doswell et al 1996;Wheatley et al 2006;Wakimoto et al 2006;Gallus et al 2008;Duda and Gallus 2010). Many mesoscale convective systems (MCSs) also spawn mesoscale convective vortices (MCVs) that can serve later as focal points for the development of new convection that may not be tied to any other large-scale forcing and can produce heavy precipitation (Fritsch et al 1994;Trier and Davis 2002).…”

Evaluation of a Cloud-Scale Lightning Data Assimilation Technique and a 3DVAR Method for the Analysis and Short-Term Forecast of the 29 June 2012 Derecho Event

“…In con- 17.5 to 110 K; at 500 m MSL, not shown) within its cold pool over southeast Indiana that is collocated with the simulated MCS's descending rear-to-front inflow reflectivity notch. Additional detailed analysis of vertical cross sections (not shown) reveal that this warm tongue arises from the fast descent of air parcels with adiabatic warming that are transported through a classical descending rear-inflow jet (RIJ), a feature often detected in radar-observed bow-echo MCSs (e.g., Wakimoto et al 2006). The tip of this warm tongue at the base of the RIJ is coincident with local wind speed maxima in excess of 25-30 m s 21 (Fig.…”

Micrometeorological Observations of a Microburst in Southern Finland

“…These radar signatures moved just north of Hyytiälä at 1415 EET (Fig. 3b), and are all considered important indicators of convective systems producing strong surface winds (e.g., Fujita 1979;Przybylinski and DeCaire 1985;Smull and Houze 1987;Przybylinski 1995;Wakimoto et al 2006). Within a mesoscale convective system, a rear-inflow jet may advect dry mid-level air into the convective system, leading to evaporative cooling of precipitation, negative buoyancy, convective downdrafts, and the bowing of the convective line (e.g., Atkins and Wakimoto 1991).…”

“…Recent numerical modelling Trapp and Weisman 2003) and observational studies (Atkins et al 2004(Atkins et al , 2005Wheatley et al 2006;Wakimoto et al 2006) have shown that the most intense straight-line winds within bow echoes are frequently associated with low-level mesovortices. In the United States, where the majority of the bow echoes move to the east or south-east, the most severe wind damage is observed north or north-west (left) of the bow echo apex in close association with mesovortices (e.g., Wheatley et al 2006).…”