163 The Role of Polarimetric, Doppler Velocity, and Spectrum Width Signatures in the Reanalysis of a QLCS Tornado Cluster

Tuesday, 29 August 2017
Zurich (Swissotel Chicago)
Richard Castro, NOAA/NWS, Romeoville, IL; and A. Lyza, A. W. Clayton, B. Borchardt, E. Lenning, M. Friedlein, and K. R. Knupp

A pair of tornadic quasi-linear convective systems (QLCSs) impacted Iowa, northern Illinois, and northern Indiana on 30 June - 1 July 2014. The second QLCS was particularly potent, producing 29 confirmed tornadoes and numerous instances of significant non-tornadic wind damage. Of the 29 confirmed tornadoes, 14 were associated with a large mesovortex in northeastern Illinois and northwestern Indiana that split into two subvortices. The northern subvortex was associated with 8 tornado tracks and the southern subvortex with 6 tornado tracks. The damage surveys for these tornadoes proved extremely difficult given the rural nature of the impacted area, the complex distribution of damage points, and a lack of high-resolution satellite imagery until after the Storm Data deadline for certifying tornado tracks. For these reasons, determination of tornado tracks for purposes of Storm Data necessarily involved integration of a conceptual model for the tornado lifespans within the larger subvortices. Several months later, newly available high resolution satellite imagery collected after the event indicated the presence of additional damage that survey crews either did not know about or could not access during the immediate post-event survey. This additional data source was the impetus for an overarching reassessment of the entire tornado cluster and a re-evaluation of the conceptual model utilized during the documentation process. Polarimetric, Doppler velocity, and spectrum width data from the Weather Surveillance Radar - 88 Doppler (WSR-88D) at Chicago/Romeoville, IL (KLOT) also were heavily employed during the damage reanalysis. This radar data aided in filling information gaps still not addressed by the survey and satellite data, thus serving as an additional source of confidence in the assessment.

In this presentation, we offer a preliminary reanalysis of the northeastern Illinois and northwestern Indiana tornado cluster from the second 30 June - 1 July 2014 tornadic QLCS. We start by detailing the methodology and reasoning for the initial (official) assessment of the tornadoes. We then discuss how the additional analysis of polarimetric, velocity, and spectrum width data, in conjunction with the newly available satellite imagery, aided in the reanalysis of the cluster of tornado tracks. Additionally, we investigate how the radar signatures corresponded to the intensity of damage observed in the survey analysis. We culminate with a refined conceptual model to hypothesize how the tornadoes evolved within the scope of the larger subvortices.

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