Examination of the low level polarimetric radar parameters associated with the August 20 2009 southern Ontario tornadic supercells

On Aug 20 2009 numerous supercells with strong rotations moved through southern Ontario. During the period from 2100 to 2230GMT 6 of these storms were observed within 60 km of the King City radar (near Toronto Canada). After an exhaustive investigation it was concluded that 4 of these supercells produced F1/F2 tornadoes while the other 2 did not. This paper will examine the structure of these 6 storms. Twelve other tornadoes were reported in southern Ontario on August 20 but will not be considered here.

The Environment Canada King City 5 cm radar has had dual polarization capability since 2004. The Aug 20 2009 outbreak provides a unique opportunity to study supercell storms at close range. This paper will concentrate on the data from a research mode high resolution 0.5 degree scan collected by King Radar every 10 minutes. For these close-in storms this scan elevation will give a view of the lowest parts of the storm, from a few hundred metres to 1 km above the ground. Polarimetric parameters at lower resolution are collected at the King City radar for the full volume scan but will not be presented here. A few papers within the last couple of years have expanded the conceptual models of supercells to include polarimetric parameters. Many of the new features of this conceptual model are observed at low levels. The zdr arc and kdp foot signatures at low levels of the storm will be reviewed here and we will examine how our supercells match this model. A study of a May 2003 Ok tornadic supercell exhibited an expansion and a storm relative clockwise rotation of the kdp foot at low levels as the tornado touched down. This work will be a main reference point for our study.