1. Comparison of PPS and QPE Rainfall Estimates for Summer 2013 Heavy Precipitation Events Comparison of PPS and QPE Rainfall Estimates for Summer 2013 Heavy Precipitation Events Mitchell Gaines National Weather Service Mount Holly, NJ

2. WFO Philadelphia/Mount Holly NJ Purpose To evaluate the PPS and QPE Algorithms and processes of rainfall estimation with relation to ground truth precipitation measurements for several heavy rainfall events from this past Summer over the Philadelphia region. Photo: Pennsville, NJ Jul 28,2013 Source: NJ.com

3. WFO Philadelphia/Mount Holly NJ Rainfall Records Broken -Wettest June and July on record at Philadelphia International Airport. -8.03 inches in about six hours (daily rainfall record) at Philadelphia on July 28 th -Wettest June on record in Wilmington, DE, and Atlantic City, NJ

4. WFO Philadelphia/Mount Holly NJ Legacy PPS vs. Dual-Pol QPE PPS -From base reflectivity (Z)  Digital Hybrid Scan -Single Z-R relation used at any time (choice of coefficients) -Gage bias adjustment available -Suffers from bright band, hail contamination, beam blockage QPE -From Z, ZDR, CC, KDP, MLDA, HCA  Digital Precip Rate -Three relations: R(Z), R(Z,ZDR), R(KDP) plus adjustments for frozen hydro-meteors -No gage bias adjustment -Dual-pol input should mitigate many PPS limitations

5. WFO Philadelphia/Mount Holly NJ WFO Mount Holly, NJ County Warning Area

6. WFO Philadelphia/Mount Holly NJ KDIX KDOX KDIX/KDOX Coverage to 150 km

7. WFO Philadelphia/Mount Holly NJ Methodology Identify heavy rainfall events over the Philadelphia region this summer which led to flash flooding. (6/3/13, 6/7/13, 6/10/13, 6/18/13, 7/1/13, 7/13/13, 7/23/13, 7/28/13) Use Multi-Radar Multi-Sensor System (MMRS) http://nmq.ou.edu/legacy2012.html http://nmq.ou.edu/legacy2012.html -Compare rain gauge data to radar estimates from both the PPS and QPE for that particular point. -Exclude data less than 20km or more than 150 km from the radar. -Excluded zero or trace values, gauge or radar.

8. WFO Philadelphia/Mount Holly NJ Methodology (Cont’d) Use of DIX and DOX WSR 88D radars to apply estimation methods. Variables measured to determine preference -RMSE, Correlation Coefficient, Mean Bias -Graphical scatter plots -Focus on July 28 th event ( 03z to 03z timeframe with scatterplots)

9. WFO Philadelphia/Mount Holly NJ July 28 th Heavy Rainfall -Localized heavy rainfall event -8.03 inches of rain in about six hours at Philadelphia International, less than one inch at Northeast Philadelphia. Dual-pol (QPE) rainfall estimate image

10. WFO Philadelphia/Mount Holly NJ Synoptic Overview, July 28

11. WFO Philadelphia/Mount Holly NJ PPS DIX Radar 7/28

12. WFO Philadelphia/Mount Holly NJ QPE DIX Radar 7/28

13. WFO Philadelphia/Mount Holly NJ PPS DOX 7/28

14. WFO Philadelphia/Mount Holly NJ QPE DOX 7/28

15. WFO Philadelphia/Mount Holly NJ Overall Results 6/7 (Andrea) DIXMean Bias G/RCorrelation CoeffRMSE (in) QPE 1.31.57.89 PPS 1.61.57 1.10 6/10 DIXMean Bias G/RCorrelation CoeffRMSE (in) QPE 1.00.77.48 PPS 1.45.76.58 6/18 DIXMean Bias G/RCorrelation CoeffRMSE (in) QPE.74.91.35 PPS.98.86.34 6/3 DIXMean Bias G/RCorrelation CoeffRMSE (in) QPE.91.80.2 PPS 1.06.78.21

16. WFO Philadelphia/Mount Holly NJ Overall Results 7/23-24 DIXMean Bias G/RCorrelation CoeffRMSE (in) QPE.73.80.52 PPS 1.13.79.35 7/28-29 DIXMean Bias G/RCorrelation CoeffRMSE (in) QPE.98.94.35 PPS 1.37.93.66 7/12Mean Bias G/RCorrelation CoeffRMSE (in) QPE.89.88.34 PPS 1.17.87.34 7/1 (12Z)Mean Bias G/RCorrelation CoeffRMSE (in) QPE.82.87.36 PPS1.27.87.32

17. WFO Philadelphia/Mount Holly NJ Average Results AVG DIXMean Bias G/RCorrelation CoeffRMSE(in) QPE.93.81.44 PPS1.26.80.49

18. WFO Philadelphia/Mount Holly NJ Conclusions -Lower mean bias with QPE -Similar CC values -Lower RMSE values with QPE, all but 7/23. - DOX results featured higher Dual-Pol totals while Legacy was a better fit in several cases.

19. WFO Philadelphia/Mount Holly NJ Conclusions QPE is preferred for rainfall amounts over 2 inches in heavy rainfall events. -Much better at “capturing” higher amounts of QPF. -Seen in “curve” throughout many of the scatterplots -Use of melting layer more of a role in cold season -Zimmerman Presentation (NWS, Wakefield)

20. WFO Philadelphia/Mount Holly NJ Special thanks to the -NROW Conference Steering Committee -NROW Conference Steering Committee -The University of Albany -National Weather Service Mount Holly, NJ -SOO Al Cope Questions