1. Tornado Detection Algorithm (TDA) By: Jeffrey Curtis and Jessica McLaughlin

2. Build 9 Typically triggered after a tornado event occurred Typically triggered after a tornado event occurred Linked to the Mesocyclone Detection Algorithm Linked to the Mesocyclone Detection Algorithm Smaller rotations missed by algorithm Smaller rotations missed by algorithm

3. Build 10 Aimed to address low probability of detection by the Build 9 Aimed to address low probability of detection by the Build 9 TDA separated from the Mesocyclone Detection Algorithm TDA separated from the Mesocyclone Detection Algorithm Built to detect significant regions of shear Built to detect significant regions of shear Higher probability of detection Higher probability of detection Distinguishes between tornadic and non-tornadic shear Distinguishes between tornadic and non-tornadic shear

4. The Algorithm 1-D pattern vectors identified 1-D pattern vectors identified Gate to gate shear – velocity difference between two adjacent range bins Gate to gate shear – velocity difference between two adjacent range bins Minimum shear value Minimum shear value Detects only cyclonic rotation Detects only cyclonic rotation

5. 1-D Pattern Vectors 112233 -4-5 -411 -5-8-6 22 -2-6 3611 -6-10-11796 -2-5-10659 -5-7-11555 -5-13-10-331 -4-2-3 47

6. The Algorithm (cont.) 2-D features created by the combination of three or more 1-D pattern vectors 2-D features created by the combination of three or more 1-D pattern vectors Classifies features in order of shear values 35, 30, 25, 20, 15 and 11 m s -1 Classifies features in order of shear values 35, 30, 25, 20, 15 and 11 m s -1 Sorts 2-D features by increasing height Sorts 2-D features by increasing height

7. 2-D Features 112233 -4-5 -411 -5-8-6 22 -2-6 3611 -6-10-11796 -2-5-10659 -5-7-11555 -5-13-10-331 -4-2-3 47

8. The Algorithm (cont.) Checks vertical continuity of 2-D features Checks vertical continuity of 2-D features  Strongest circulation declared base 3-D features composed of a minimum of three 2-D features 3-D features composed of a minimum of three 2-D features  Ideal case of no gaps within elevation sweeps  No more than one elevation scan gap

9. Fig. 1. A schematic of a 3D vortex formed by three 2D vortices. (Mitchell et al, 1998)

10. Tornado Vortex Signature (TVS) 3 dimensional circulation 3 dimensional circulation Base extends to the 0.5 radar elevation height or has a base below 2000ft. (600m) above radar level Base extends to the 0.5 radar elevation height or has a base below 2000ft. (600m) above radar level Shown by a red triangle and is coded red in the table Shown by a red triangle and is coded red in the table

11. TVS (cont.) Minimum velocity difference required is 25 ms -1 Minimum velocity difference required is 25 ms -1 Circulation depth of at least 1.5 km Circulation depth of at least 1.5 km

12. Elevated Tornado Vortex Signature (ETVS) 3 dimensional circulation 3 dimensional circulation Base does not extend to the 0.5 radar elevation height and has a base above 2000ft. (600m) above radar level Base does not extend to the 0.5 radar elevation height and has a base above 2000ft. (600m) above radar level Shown by a yellow triangle and is coded yellow in the table Shown by a yellow triangle and is coded yellow in the table

13. ETVS (cont.) Minimum velocity difference required is 36 ms -1 Minimum velocity difference required is 36 ms -1 Circulation depth of at least 1.5 km Circulation depth of at least 1.5 km

14. Positives of TDA Uses gate to gate instead of only strong shear values Uses gate to gate instead of only strong shear values gate to gate is more closely related to tornadic circulation gate to gate is more closely related to tornadic circulation Mesocyclone does not need to be present to search for strong velocities Mesocyclone does not need to be present to search for strong velocities Searches all velocity pairs Searches all velocity pairs

15. Positives (cont.) More information given to the observer More information given to the observer Can determine shear type (TVS or ETVS) Can determine shear type (TVS or ETVS) Can determine base or depth of the circulation Can determine base or depth of the circulation Parameters can be changed to allow for better performance Parameters can be changed to allow for better performance Can allow for a higher probability of detecting significant regions of shear Can allow for a higher probability of detecting significant regions of shear

16. Negative of TDA Doesn’t detect areas of anti-cyclonic rotation Doesn’t detect areas of anti-cyclonic rotation High FAR (False Alarm Rate) High FAR (False Alarm Rate) Can cause too many warnings to be made to the public Can cause too many warnings to be made to the public Build 9 had lower FAR Build 9 had lower FAR

17. Negatives (cont.) Relationship between tornadoes and ETVS is not fully researched Relationship between tornadoes and ETVS is not fully researched Must fully complete radar scan before TVS/ETVS is resolved Must fully complete radar scan before TVS/ETVS is resolved

18. Using the Tornado Detection Algorithm Important features to look for: Important features to look for: Position of the algorithm in relationship to the storm Position of the algorithm in relationship to the storm Length of time that the TVS has been present Length of time that the TVS has been present Distance from radar Distance from radar Environmental winds Environmental winds

20. References Mitchell, E.D., 1998: The National Severe Storms Laboratory Tornado Detection Algorithm. Wea. Forecasting, 9, 352-366. Mitchell, E.D., 1998: The National Severe Storms Laboratory Tornado Detection Algorithm. Wea. Forecasting, 9, 352-366. The National Severe Storms Laboratory Tornado Detection Algorithm: Documentation. http://www.nssl.noaa.gov/wrd/swat/mitchell/nssl _tda.html The National Severe Storms Laboratory Tornado Detection Algorithm: Documentation. http://www.nssl.noaa.gov/wrd/swat/mitchell/nssl _tda.html http://www.nssl.noaa.gov/wrd/swat/mitchell/nssl _tda.html http://www.nssl.noaa.gov/wrd/swat/mitchell/nssl _tda.html The NSSL Tornado Detection Algorithm (TDA), and Its Use for the 1996 Warning Decision Support System (WDSS) Proof-of-Concept (PoC) Tests. http://www.nssl.noaa.gov/wrd/swat/mitchell/tda wdss96user2.html The NSSL Tornado Detection Algorithm (TDA), and Its Use for the 1996 Warning Decision Support System (WDSS) Proof-of-Concept (PoC) Tests. http://www.nssl.noaa.gov/wrd/swat/mitchell/tda wdss96user2.html http://www.nssl.noaa.gov/wrd/swat/mitchell/tda wdss96user2.html http://www.nssl.noaa.gov/wrd/swat/mitchell/tda wdss96user2.html