Tuesday, 8 January 2019: 12:00 AM
North 132ABC (Phoenix Convention Center - West and North Buildings)
To better understand, evaluate, and communicate real-time tornado threats, the Storm Prediction Center (SPC) has worked toward calculating gridded probabilities of tornado intensity (conditional on the existence of a tornado) by deriving statistical relationships between tornado EF-scale ratings, manually-calculated radar-derived circulation attributes (rotational velocity and shear diameter), and environmental significant tornado parameter (STP) values. While the preliminary tornado intensity models have shown utility, rotational velocity (Vrot) and shear diameter cannot be objectively calculated in an automated real-time sense, preventing the probability products from operating in a real-time environment and effectively limiting their applicability in short-fuse warning-decision operations. To overcome this, SPC and CIMMS researchers are collaborating to develop conditional probability of tornado intensity (CPTI) products capable of producing real-time, CONUS-wide tornado intensity estimation probability grids. To do so, azimuthal shear —a gridded estimate of rotation strength that is calculated in real-time within the NWS Multi-Radar Multi-Sensor (MRMS) suite of products—replaced the manually-derived input of Vrot. Using a comprehensive SPC severe storm report database from 2014-15, a quantitative relationship between AzShear and Vrot was derived, effectively bridging the two measures of rotation and allowing azimuthal shear to be utilized in the automated real-time CPTI product. A technique was also developed to derive shear diameter from single-radar velocity data, which are then merged together from multiple single radars to form a merged gridded shear diameter product. Following the development and integration of these two real-time input products for CPTI, a logistic regression model was constructed using the same two-year dataset, providing a platform to generate real-time tornado intensity probability grids.
This presentation reviews the methodology and initial testing of the new AzShear-based CPTI gridded product, including discussions of AzShear-Vrot relationships, shear diameter calculations, logistic regression model creation, and the output of the prototype gridded CONUS probability products. Finally, plans for real-time testing of CPTI during Spring 2019 in the Hazardous Weather Testbed will be outlined.
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