TORP/AzShear for Sidelobe Event

A case of sidelobe contaminated velocity fields occurred around 1945 UTC (Thursday) in Ralls County, Missouri. TORP/AzShear algorithms were quick to initiate an object and jump towards near certain (>90%) values. The object remained for multiple volume scans until sidelobes disappeared. When “real” velocities emerged, TORP magnitudes dropped/went below threshold quickly.  -QLCS

QLCS Orientation Vs. Radar and AzShear Patterns

A short observation. Looking at an incoming QLCS line from KDOX creates two different regimes of AzShear patterns depending upon how parallel to the radial it’s aligned.  We see groups of couplets on the more perpendicular side and a long stretch of convergence/divergence paired on the parallel side.

Meanwhile, TORP still isn’t really sure how to handle this…

-Wx Warlock

Strange TORP Object Location Near Radar

Found a questionable TORP object while skimming through a case this afternoon. A few broken lines of convection are approaching the KAKQ radar on an early February morning. I had yet to see many TORP objects as the case is a bit of a slow start, but suddenly noticed this pop up centering on the west side of an oncoming line.

Indication of TORP on the west side of the convective line suspiciously pinging along I-85.

I found this strange, as I not would expect AzShear values to hug that close to the west side of a line. So I went to investigate with reflectivity and velocity data and didn’t find anything I was impressed with.

A normal looking convective line approaches KAKQ.

What I did see, is that the TORP object is centered about a section of I-85 in a section of fairly low reflectivity. In my home office, we’ve seen cars and boats via radar and this could be a similar event, but with a convective line in the way there’s no real way to be sure.

-Wx Warlock

Shorter TORP Timescales on QLCS Case

Most of the TORP objects in this case had very short timescales. This is an example from a tornadic mesovortex where TORP did pick up higher probabilities, but just for a short time. This is largely due to the nature of the storm mode as QLCS tornadoes (and QLCS signatures in general) are quicker and more transient in nature. In previous cases with supercells, the timescale is usually longer.

-Stormy Surge

TORP Performance for QLCS Case(s)

As has been noted, TORP lead time is nearly non-existent when it comes to QLCS events. This is especially true when applying a threshold filter >40-50%. However, in this case and others assessed so far this week, FAR with TORP is relatively low for even these marginal/transient cases. The example above displays nearly zero lead time to confirmed event (~1244 UTC), though would be eye-catching should a TOR warning not yet be in place.  -QLCS

Low TORP Probability Next to Radar

An area of higher AzShear moved close to the KLWX radar at 1221z and TORP struggled to pick up on this. TORP has a known QC to filter out data within a certain range (30km) from the radar, but even when that was turned off, TORP did not have anything. 

Looking at the velocity data, there is a couplet there just to the northwest of the radar where AzShear is maximized. So, even though AzShear responded well to the couplet, TORP struggled due to the close proximity to the KLWX radar.

The TORP graph shows that when the couplet with the high AzShear moved farther away from the radar, the probabilities shot up from 25% to 80%. And this couplet did produce a tornado.

-Stormy Surge