1. Analysis of Radar-Rain Rate Relations During the Southeast Texas Flood Event of 18 April 2009 Steve Vasiloff, NOAA/National Severe Storms Laboratory Jeffrey Lindner, Harris County Flood Control District Lance Wood, NOAA/National Weather Service, Houston 2010 National Flood Workshop, Houston, TX

2. Outline Radar reflectivity rainrate (Z-R) relations Radar resolution impacts Heavy rain and wind impacts on gauges 5 and 1-min radar and gauge comparisons Examples of radar and gauge uncertainties Concluding remarks

3. Harris County Flood Control District gauges

4. NSSL Q2 system http://nmq.ou.edu Next-generation quantitative precipitation estimation (QPE) system 1 km resolution CONUS every 5 min Multisensor products Dynamic Z-R Q2 radar-based used as base field for West Gulf RFC operations (with local gauge correction) Other RFCs “cut and paste” Q2 into their systems

5. Q2 main page

6. TS Nicole example Q2 Z-Rs

7. TS Nicole example Q2 reflectivity

8. Radar reflectivity-rainrate relations

9. Radar data resolution

10. KHGX super-res

11. Q2 1-km res 180 * * 130

12. 5-min Q2 dBZ; gauge data convective & tropical Z-Rs 5 min data are aggregated from 1 st to 5 th min past top of the hour Gauge Convective QPE Tropical QPE Q2 5-min reflectivity

13. 5-min Q2 dBZ & gauge data convective & tropical Z-Rs Q2 5-min reflectivity Gauge Hi-res reflectivity

14. 1-min hi-res KHGX & gauge Gauge Hi-res reflectivity

15. 5-min Q2 dBZ; gauge data convective & tropical Z-Rs 5 min data are aggregated from 1 st to 5 th min past top of the hour Q2 5-min reflectivity Gauge Convective QPE Tropical QPE

16. 1-min hi-res KHGX & gauge Gauge Hi-res reflectivity

17. Radar clutter filter “zero isodop” line

18. Radar clutter filtering Radar echo minima due to filter?

19. 5 min sampling – constant rainrate for QPE Echo motion

20. Gauge networks

22. Summary Urban FF warnings require hi-res data 1 –min data too noisy? High rainrates and winds reduce confidence in gauge data – difficult to quantify undercatch – 15-30%???? Clutter filter causes uncertainty in radar data Need better gauge-radar metadata – Know which gauges are in clutter, zero isodop Gauge QC is an ongoing issue

23. Q2 future Higher resolution – 2.5 min radar (NEXGEN) – 10-15 min gauge MADIS/additional gauge networks (HCFCD) Gauge quality control algorithm – Using temporal analysis of radar-gauge bias – Spatial checks – Gauge Quality Index