Characteristics of Sub-diurnal Extreme Precipitation-Producing Systems

1. Characteristics of Sub-diurnal Extreme Precipitation-ProducingSystems Nathan M. Hitchens Robert J. Trapp Michael E. Baldwin

2. Motivation • Significant impact on life, property, and agriculture • Little focus on precipitation at time scales less than daily • Little quantitative data available to assess the predictability of the systems that produce extreme precipitation

3. Extreme Precipitation Example Radar reflectivity from 0500 to 0600 UTC

4. 1-hr Accumulated Precipitation Maximum precipitation: 62 mm

5. 3 6 9 12 1 1 1 1 1 3 3 3 3 3 2 2 Methods • Feature-specific approach • Baldwin Object-Oriented Identification Algorithm (BOOIA)

6. Size: 15,856 km2 28 August 1998 @ 0600 UTC Precipitation Precipitation BOOIA Output BOOIA Output BOOIA Output #21 • Maximum: 62 mm

7. Methods • Data • Stage 2 precipitation data: May 1996 – Dec 2008 (hourly) • Multi-sensor product • Analysis • BOOIA applied to each hour • Attributes include: • Object size • Maximum precipitation Midwestern United States Region

8. Precipitation Objects 99th Percentile

9. Precipitation Analysis • Threshold of 55 mm for ‘extreme’ • BOOIA identified 2,733 occurrences of extreme precipitation identified in Midwest • Mean extreme precipitation object has size of 8,000 km2 and maximum precipitation of 68 mm

10. Precipitation Analysis • Mean object size: 7,808 km2 • Standard deviation: 9,972 km2 • Minimum: 176 km2 • Maximum: 126,080 km2

11. Precipitation Analysis

12. Characteristics of precipitation not sufficient to characterize systems that produce it Analysis of reflectivity better suited for this Precipitation Analysis

13. Methods (Cont.) • Data • NOWrad reflectivity available 1996 – 2008 (quarter hourly) • Analysis • Apply BOOIA to reflectivity mosaic from halfway through the hour of accumulation for each extreme precipitation occurrence • Match precipitation object with nearest reflectivity ‘entity'

14. Size: 15,856 km2 28 August 1998 @ 0600 UTC Precipitation Precipitation BOOIA Output BOOIA Output BOOIA Output #21 • Maximum: 62 mm

15. 28 August 1998 @ 0530 UTC Reflectivity BOOIA Output #11 • Maximum: 56 dBZ • Size: 162,320 km2

16. Mean entity size: 32,180 km2 Standard deviation: 47,365 km2 Minimum: 80 km2 Maximum: 393,664 km2 Reflectivity Analysis

17. In the mean, the smallest extreme precipitation-producing systems occur in the summer months Reflectivity Analysis Entity Size (km2) Season

18. Reflectivity Analysis Entity Size (km2) Time of Day • Smallest extreme precipitation-producing systems occurring in late afternoon (individual cells or small cluster of cells), opposed to larger during overnight hours (larger MCSs)

19. Take-home Point • Sizes of extreme precipitation-producing convective systems range from single, relatively isolated cells to large convective systems • Smaller systems are more common producers of extreme precipitation than typically considered

20. Ongoing Work • Simulating specific events using Weather Research and Forecasting (WRF) model to assess predictability of extreme hourly precipitation-producing systems WRF (NARR: 32 km) Stage 2 WRF (R1: 210 km)

21. Acknowledgements NSF ATM 0541491 Data provided by NCAR/EOL under sponsorship of the National Science Foundation. http://data.eol.ucar.edu/ This is part of a larger collaborative effort, advancing Purdue’s Climate and Extreme Weather (CLEW) initiativenmhitchens@purdue.edu

22. Reflectivity Analysis Threshold of 35 dBZ maximum for matched entities, but entities defined by threshold of 20 dBZ Identified 1,249 entities that matched with an occurrence of extreme precipitation Mean matched entity has size of 32,000 km2 and maximum reflectivity of 47 dBZ