Radar and model-based studies of mesovortices in cool-season quasi-linear convective systems

Blind-Doskocil, Leanne Nicole

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https://hdl.handle.net/2142/121541 Copy

Description

Title

Radar and model-based studies of mesovortices in cool-season quasi-linear convective systems

Author(s)

Blind-Doskocil, Leanne Nicole

Issue Date

2023-07-18

Director of Research (if dissertation) or Advisor (if thesis)

• Trapp, Robert J
• Nesbitt, Stephen W

Committee Member(s)

Kosiba, Karen

Department of Study

Atmospheric Sciences

Discipline

Atmospheric Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• QLCS
• Quasi-Linear Convective System
• mesovortex
• tornado
• tornadic
• nontornadic
• PERiLS
• Propagation, Evolution, and Rotation in Linear Storms
• DOW, Doppler On Wheels
• C-band On Wheels
• radar
• WSR-88D
• NEXRAD
• updraft helicity
• low-level rotation
• severe weather
• WRF
• Weather Research and Forecasting model
• HRRR
• High-Resolution Rapid Refresh model
• forecasting tornadoes
• tornado warning
• Pod
• wind-damaging

Abstract

The challenges associated with forecasting quasi-linear convective system (QLCS) tornadoes are well-documented. QLCS tornadoes typically form within a parent vortex known as a mesovortex (MV); however, not all MVs are tornadic, which adds to the forecasting challenge. The Propagation, Evolution, and Rotation in Linear Storms (PERiLS) field campaign was conducted in the springs of 2022 and 2023 to collect high-resolution observations on tornadic QLCSs. This three-part study examined (i) the predictability of tornadic QLCSs using the High-Resolution Rapid Refresh (HRRR) atmospheric model to forecast for PERiLS deployments, (ii) the characteristics that differentiate tornadic (TOR), wind-damaging (WD), and non-damaging (ND) QLCS MVs using the WSR-88D radar data and PERiLS COW radar and Pod data, and (iii) a WRF simulation of PERiLS 2022 IOP2 to further investigate MV characteristics. For part 1 of this study, 97 tornadic cool-season QLCS cases were analyzed to examine whether the HRRR proved useful in predicting the convective mode of QLCSs and whether maximum 2-5 and 0-2 km updraft helicity (UH) values could be used to predict tornadoes. The HRRR modeled a QLCS in all cases for forecast hours 18, 12, and 6, although the timing of the line passages was delayed in some cases. 18-hour forecasts of maximum 2-5 km UH values have similar skill in predicting tornado locations as the 6-hour forecasts of maximum 0-2 km UH values. For part 2, 21 QLCS MVs were identified and catalogued using the WSR-88D and COW radars during the two years of PERiLS. It was found that TOR MVs over their total lifetimes have stronger rotational velocities (Vrots), smaller diameters, and slightly longer lifetimes when compared to WD and ND MVs. Although TOR and WD MVs have similar Vrots when analyzed prior to the first report/warning, TOR MVs typically have smaller diameters, which could be useful to forecasters. Three of the MVs intercepted six Pods during the deployments. A wind shift was detected by each of the Pods with a maximum wind gust of 11.84 m/s observed, and five of the six Pods observed a decrease in pressure. Time-height profiles of Vrot of a TOR MV and ND MV displayed that the TOR MV was associated with a mid-level circulation at the time of tornadogenesis. Finally, for part 3, analysis of two MVs using WRF revealed that the stronger MV was associated with stronger winds and a surface pressure drop at its peak intensity, and it was also deeper over most of its lifetime. This three-part study has advanced our understanding of predicting tornadic QLCSs using the HRRR and discriminating tornadic from nontornadic QLCS MVs.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Leanne Nicole Blind-Doskocil

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