HSLC Radar Climatology Update

Jason DavisJuly 26, 2012

Current Status

• Developing a climatology of tornadic and non-tornadic HSLC mesocyclones/mesovortices.

• Goal: Help forecasters determine if a mesocyclone/mesovortex observed in radar velocity data will be tornadic or non-tornadic.

Current Status

• Do this by collecting statistics for a large population of mesocyclones/mesovortices.

• Currently in final stages of developing an automated method of tracking and recording information about them.

• Will use tornadic circulations as well as circulations associated with false alarm tornado warnings/non-tornadic MDA detections.

Method

• Record max azimuthal shear value for each circulation at each time and radar tilt that it exists.

• Higher azimuthal shear value = stronger couplet for circulations.

• Azimuthal shear is what is used for “rotation track” maps, and is also similar to NROT.

Azimuthal Shear

• Calculation is similar to

• But it uses velocity data from multiple bins rather than just the max outbound/max inbound through a linear least squares technique.

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Tracking circulations

• Currently developing a method for tracking circulations.

• Uses input from MDA (if triggered) and cell tracking algorithms, with QC measures to account for algorithm limitations.

Potential calculations

• Calculations will include comparisons between tornadic and non-tornadic circulations:– Maximum azimuthal shear during a circulation’s lifetime.– Circulation lifetime (length of time that azimuthal shear is above

a certain threshold)– Depth of circulation.– Changes in circulation depth/strength over time.– Time series plots of azimuthal shear in a tornado-relative time

coordinate system.– PODs/FARs for these statistics.

• Will also look at how these statistics vary by convective mode and range from the radar.

Questions to answer

• Are tornadic circulations stronger, longer-lived, and deeper than non-tornadic circulations?

• What % of HSLC tornadoes are preceded by rotation aloft?

• What shear thresholds could be useful for detecting HSLC tornadoes?

• What % of HSLC tornadoes are reasonably detectable, and how does this change with range from the radar?

Possible Future Work

• What % of broken S signatures produce tornadoes?• Do tornadic HSLC storms tend to have higher echo

tops/reflectivity at higher tilts compared to non-tornadic HSLC storms—can looking for stronger cores help focus which areas of a QLCS warrant the most attention?

Smith et al. 2012