Analysis of Radar-Rain Rate Relations During the Southeast Texas Flood Event of 18 April 2009
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Transcript of Analysis of Radar-Rain Rate Relations During the Southeast Texas Flood Event of 18 April 2009
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Analysis of Radar-Rain Rate Relations During the Southeast
Texas Flood Event of 18 April 2009
2010 National Flood Workshop, Houston, TX
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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
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Harris County Flood Control District gauges
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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
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Q2 main page
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TS Nicole exampleQ2 Z-Rs
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TS Nicole exampleQ2 reflectivity
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Radar reflectivity-rainrate relations
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Radar data resolution
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KHGX super-res
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Q2 1-km res
180 ** 130
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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
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5-min Q2 dBZ & gauge dataconvective & tropical Z-Rs
Q2 5-min reflectivity
Gauge
Hi-res reflectivity
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1-min hi-res KHGX & gauge
Gauge
Hi-res reflectivity
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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
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1-min hi-res KHGX & gauge
Gauge
Hi-res reflectivity
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Radar clutter filter “zero isodop” line
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Radar clutter filtering
Radar echo minima due to filter?
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5 min sampling – constant rainrate for QPE
Echo motion
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Gauge networks
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Gauge networks
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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
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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