Analysis of Radar-Rain Rate Relations During the Southeast

Texas Flood Event of 18 April 2009

2010 National Flood Workshop, Houston, TX

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

Harris County Flood Control District gauges

NSSL Q2 systemhttp://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

Q2 main page

TS Nicole exampleQ2 Z-Rs

TS Nicole exampleQ2 reflectivity

Radar reflectivity-rainrate relations

Radar data resolution

KHGX super-res

Q2 1-km res

180 ** 130

5-min Q2 dBZ; gauge dataconvective & tropical Z-Rs

5 min data are aggregated from 1st to 5th min past top of the hour

Gauge

Convective QPE

Tropical QPE

Q2 5-min reflectivity

5-min Q2 dBZ & gauge dataconvective & tropical Z-Rs

Q2 5-min reflectivity

Gauge

Hi-res reflectivity

1-min hi-res KHGX & gauge

Gauge

Hi-res reflectivity

5-min Q2 dBZ; gauge dataconvective & tropical Z-Rs

5 min data are aggregated from 1st to 5th min past top of the hour

Q2 5-min reflectivity Gauge

Convective QPE

Tropical QPE

1-min hi-res KHGX & gauge

Gauge

Hi-res reflectivity

Radar clutter filter “zero isodop” line

Radar clutter filtering

Radar echo minima due to filter?

5 min sampling – constant rainrate for QPE

Echo motion

Gauge networks

Gauge networks

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

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