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An Objective Climatology of Rotational Velocity of High Shear/Low CAPE Tornadic Storms in the Southeast and Mid-Atlantic

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Wednesday, 5 November 2014
Capitol Ballroom AB (Madison Concourse Hotel)
Justin D. Lane, NOAA/NWS Forecast Office, Greer, SC

While the limited research that has been dedicated to the study of convection occurring in high shear/low CAPE (HSLC) environments has typically treated the phenomena as a special case or “sub-category” of severe convection, recent climatological studies have shown that HSLC is the “typical” environment associated with tornadic convection across much of the Southeast and Mid-Atlantic. Perhaps the primary challenge associated with operational forecasting of HSLC convection is the tendency for tornadic convection to exhibit “non-classical” and/or weak and transient signatures from a radar observation perspective. Because much of the National Weather Service (NWS) training initiatives providing guidance for Tornado Warning decision making focus on “classical” (i.e., high shear/high CAPE) convection, this guidance often fails for the “typical” Southeast/Mid-Atlantic tornadic storm. Very recent Collaborative Science, Technology, and Applied Research (CSTAR) investigation has attempted to address this problem through development of a radar climatology of HSLC severe convection. However, the rotational shear and velocity component of this climatology was developed using “azimuthal shear,” an algorithm that is not directly available within the NWS at the current time. The current work attempts to expand upon this CSTAR research through development of a three-year climatology of rotational velocity (VR) associated with Southeast/Mid-Atlantic tornadic storms. Concordantly, because the Gibson Ridge Level II Analyst (GR2Analyst) software is widely used in the NWS, a “normalized rotation” (NROT) climatology is being developed. The climatology is stratified based upon three basic modes of HSLC convection that have been identified: 1) mini-supercells with classic radar reflectivity signatures, 2) mini-supercells with “non-classical” radar reflectivity signatures, and 3) quasi-linear convective systems (QLCS). These studies differ from previous radar climatologies in that there is a focus on the temporal trends in VR (and NROT) within the 0 to 20 minute window prior to tornado occurrence. The goal is to identify important trends in the data that may assist forecasters in issuing Tornado Warnings with adequate lead time.