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Using the Weather Research and Forecasting Model (WRF) at 12 km resolution driven by the Community Climate System Model 4 (CCSM4), potential changes are examined in several precipitation characteristics during future climates. WRF runs were analyzed for the winter and summer seasons for a historic period (1995 – 2004) and a future period (2085 – 2094- incorporating a business-as-usual high emissions scenario). A comparison of temperature, water vapor mixing ratio, and wind speed and direction between the historic and future periods was completed in order to gain a better understanding of future large-scale pattern changes. Utilizing the data from a storm identification and tracking algorithm (Chang et al. 2016), a regional analysis comparing historic and future WRF runs examines multiple convective precipitation characteristics in a lagrangian frame of reference. Results indicate warmer temperatures and higher water vapor content across the entire North American domain, weaker upper level winds across most of the contiguous United States. Several regional differences in future PWAT distributions and convective precipitation area characteristics (total amount of area covered and total number of convective elements per region) are also examined, and show more precipitable water (both within convective areas and in the free atmosphere).

Co-Authors: Dr. Robert Jackson (Argonne National Laboratory), Dr. Jiali Wang (Argonne National Laboratory)

Tornadogenesis in supercell thunderstorms has been a heavily studied topic by the atmospheric science community for several decades. However, the reasons why some supercells produce tornadoes, while others in similar environments and with similar characteristics do not, remains poorly understood. For this study, tornadogenesis failure is defined as a supercell appearing capable of tornado production, both visually and by meeting a vertically contiguous differential velocity (∆V) threshold, without producing a sustained tornado. Data from a supercell that appeared capable of tornadogenesis, but which failed to produce a sustained tornado, was collected by the Atmospheric Imaging Radar (the AIR, a high temporal resolution radar) near Denver, CO on 21 May 2014. These data were examined to explore the mechanisms of tornadogenesis failure within supercell thunderstorms. Analysis was performed on the rear-flank downdraft (RFD) region and mesocyclone, as previous work highlights the importance of these supercell features in tornadogenesis. The results indicate a lack of vertical continuity in rotation between the lowest level of data analyzed (100 m AGL), and heights aloft (> 500 m AGL). A relative maximum in low-level ∆V occurred at approximately 100 m AGL (0.5° in elevation on the radar) around the time of suspected tornadogenesis failure. This area of low-level rotation was unable to maintain a sustained connection with more intense ∆V patterns observed in the mesocyclone (> 2 km AGL). Additionally, the RFD produced by the Denver Supercell had a peak in intensity between approximately 3 and 3.5 km AGL just prior to the time of tornadogenesis failure, while simultaneously experiencing a relative minimum in intensity in the layer between the surface and 1 km.

Co-Authors: Dr. David Bodine*, Dr. Casey Griffin* , Andrew Mahre*, Dr. Jim Kurdzo*, Dr. Victor Gensini (Northern Illinois University)

*Advanced Radar Research Center - University of Oklahoma