May 17, 2019 Southwest Kansas Tornadic Supercell

Part II: Applying Modern Interrogation Principles to Anticipate Tornadogenesis

As discussed in Part I, a long-lived supercell occurring over southwest Kansas on 17 May 2019 was noteworthy for persisting nearly six hours including numerous severe weather reports. The existence of this supercell during the evening hours allowed it to tap into a developing low-level jet (LLJ) and associated surge of low-level shear (e.g. 0–1-km SRH >200 m2 s2) that typically increases the potential for low-level mesocyclone intensification. This launched a period with several long-track, significant tornadoes starting immediately prior to the onset of an EF3 tornado near Minneola Kansas. However, this EF3 tornado began as a missed event as the warning polygon did not include the geographical region where the vortex tracked in the first 10 minutes. While subsequent warnings used nearly continuous tornado reports and radar data to create precise polygons, this study assesses if new radar interrogation methods would have assisted in polygon timing and placement with this first significant tornado.

Although the remnant mid-level mesocyclone and horizontal reflectivity factor (ZH) “hook” structure were evident enough to pinpoint a general area of interest, genesis occurred away from these features in a region of minimal ZH, closer to a new mid-level mesocyclone. Specifically, downdraft boundary positioning reveals the pendant and remnant mesocyclone undercut by colder, more stable air that typically inhibits genesis. In contrast, modern Dual-Polarization interrogation techniques such as a ZDR arc indicated the potential for intensification with a developing, weak low-level mesocyclone tracking along the downdraft boundary. Given the storms proximity (≈20–25 nm) to the KDDC WSR-88D, a well-defined storm-relative velocity enhancement (SRVE) found emanating out of the new forward flank downdraft region, also contained a momentum surge. This momentum surge starts at 15 minutes before genesis and matches numerical simulations showing this as an airstream of near-surface horizontal vorticity feeding directly under the low-level mesocylone prior to tornadogenesis. All of this infers enough evidence well before the onset of the EF3 vortex, that the new low-level mesocyclone was likely to intensify enough to be able to stretch this near-surface vorticity into the vertical to become a tornado.

Aaron W. Johnson
NOAA/NWS Weather Forecast Office, Dodge City, Kansas

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