Developing a Climatology of Rotating Storms Using the MYRORSS Dataset

A climatology of rotation associated with deep convective storms from 1999 to 2011 is developed using a quality-controlled WSR-88D derived dataset. The Multi-Year Reanalysis of Remotely Sensed Storms (MYRORSS) dataset is a synthesis of WSR-88D and model analysis data developed with the Multi-Radar Multi-Sensor (MRMS) framework that covers the contiguous United States with high spatial and temporal resolution. One of the desired outcomes during development was to use MYRORSS to develop climatologies of convective storms. An overwhelming majority of strong tornadoes and large hail are associated with storms characterized by rotating updrafts. Developing a climatology of rotating storms may help to provide a hazard climatology that is less prone to errors commonly associated with those created from severe storm reports, such as population density bias. Daily accumulated low-level and mid-level azimuthal shear data is regridded from a 0.005° by 0.005° grid (roughly 500 m by 500 m) to a more coarse horizontal resolution of 20 km by 20 km and subsequently smoothed to determine the annual frequency of rotating storms across the continental United States. Mid-level rotation and low-level rotation are observed at similar frequencies in the Great Plains, indicating that the majority of low-level rotation is likely associated with supercell storms. However, in the Southeast, low-level rotation is observed much more frequently than mid-level rotation. This indicates that shallow rotation associated with quasi-linear convective systems likely makes up a substantial portion of rotating storms in the Southeast. Visible in the long-term climatology are both an increase in detection of rotation near WSR-88D sites and an undersampling of rotation in regions of poor WSR-88D coverage. Methods for correcting these anomalies will be explored.