CPTI and Azshear

Tracking this northern most SC @ 1926 UTC prior to tornadogenesis.  Azshear 0-2 km product did a nice job highlighting shear with developing storm very early on in storm evolution and was very persistent in highlighting area of shear throughout.  Temporal continuity was very good.  Lower two panels are 80 and 110 mph intensity probabilities.  Used this 4-panel to monitor evolution.  Also displayed is legacy mesocyclone (upper-right), DMD (lower right) and XDMD l(lower left).  This SC also exhibited well-organized ZDR arc and KDP foot (not shown) that whose centroids were normal to storm motion suggesting MC intensification was likely.

1938 utc Azshear still showing strong signal with CPTI gradually increasing to near 60%.  ProbTor increased to 78% as well.  DMD, XDMD and MD not showing much and did not seem to be very helpful.


CPTI was insightful with increasing probabilities of tornado intensity probabilities at higher speeds (110 mph lower right).   Note that XDMD was also indicating MXRV of 26.


1448 UTC – would occasionally see dual maxes in AZShear and CPTI products that was a bit of an issue at times.

CPTI 110 probablities up to ~ 75 % at this time (lower right)

Overall…0-2 km Azshear was quite helpful in quickly grabbing attention to areas of concern.  0-2 km product was temporally very consistent.  Its location relative to developing Mesocyclone was typically off…but still very useful.    XDMD, did seem to perform better than legacy DMD products but not much at least with this storm.   Early in storm evolution, examining ZDR/KDP centroids relative to storm motion was also helpful as a reality check on MC intensification and increasing SRH with this particular storm.  Bottom line was generally pleased wiith  AzShear and CPTI performance for this storm. – Quik TWIP

CPTI Usefulness

Here’s a look at some attempts to use the CPTI for storm carrying a theoretical tornado warning. I have a fair number of thoughts on the product. In terms of a primary application. I think it would be best suited to the first update/continuation on a tornado warning. Basically allowing you to chose what types of language to use…if the CPTI is picking up on a very high intensity circulation than you are going to want to ramp up the intensity of the wording within a warning. This could be used to communicate how dangerous a storm is. Especially since the damage associated with a 80mph circulation will be drastically different from a 170+ mph circulation.

Now for areas that I would improve/and or change. The CPTI might be better off using a category scale/range of values. Intuitively, I would expect probabilities to increase if the storm is more intense. I.E. if the circulation is 155mph then I might expect the 80mph CPTI to be close to say 80% while the 155 mph CPTI is something like 50%. If the tornado intensifies maybe the 80mph CPTI would increase to something like 95% while the 155 mph CPTI increases to a value such as 75%. Currently, there are a lot of very similar values as the image below shows 80, 95, 110, and 125 mph all have pretty much the same value within 3% of one another. I would want there to be a much larger variance in these values, so that I  could easily gauge , how intense the tornado is. I think CPTI has a  great potential, but I would change it so that it was more of an probability of exceedence  scale and could be used as a quick product to determine intensity wording in products.

South Beach


SC Entering Washington County

This storm has had consistent Azhear max for past several volume scans, but again does not seem to match low-level SRM scans very well. Prob Tor has increased and remained steady at about 75 to 77 % CPTI has remained slightly over 50%. Upgraded SVR to Tor possible. Reflectivity structure suggests increasing organization with well organized ZDR arc arc suggesting increasing SRH. May upgrade to tor shortly given better storm structure in base data. Quick Twip

AZShear and CPTI Product for TUL SC

Watching storm northeast of Hominy @ 1854 utc. 0-2 km AzShear has been showing persistent max with the cell but seemed to displaced to far west of broad circulation. 0-2 kn Azshear not very helpful with this storm given displacement. CPTI has been showing consistent 50-55% 80 mph intensity probs for past several scans.  – quik twip

Az Shear – the goods and bads

Photo above shows a double maximum in AzShear. One of these is clearly colocated with a TOR on ground via CC. However, velocity shows two very different situations, possible strong tornado on ground versus convergence along the RFD gust front. If you were just looking at the AzShear product, both of these areas would be cause for concern, when in fact the impacts are extremely different. Would be nice to be able to differentiate between extreme high values of AzShear near a tornado versus more broad convergence on any wind shift area.



This next image shows a region where the AzShear maximum is too broad. This may simply be a color table issue, but clearly there is an area within the white region where a tornado is on the ground, and other regions within that max where only general convergence is occurring.


This image shows a location where some ground clutter is producing a false positive and negative AzShear couplet. Mathematically it makes sense to see this here given the V data, however to an untrained eye or someone just solely depending on AzShear you could be led astray.


A positive of AzShear is that it can highlight areas of potential concern down the road. The above frame was just one of several frames showing strong convergence and high AzShear values preceding a second tornado from the main cell 10 minutes later. This could be particularly helpful in QLCS storm modes where convergence and shear increases in a broad sense along the main line prior to tornadogenesis. Also in this particular case, the V data was not entirely conclusive that convergence was increasing. AzShear was very conclusive here.


Dusty Davis