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The April 18 th 2009 Extreme Rain Event Presentation by Lance Wood

The April 18 th 2009 Extreme Rain Event Presentation by Lance Wood. My house. Image Courtesy: Galveston Daily News. Friendswood, TX. Taylor Lake Village, TX. The April 18 th 2009 Extreme Rain Event. 19 Z. The April 18 th 2009 Extreme Rain Event. 24 Hour Rainfall.

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The April 18 th 2009 Extreme Rain Event Presentation by Lance Wood

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  1. The April 18th 2009 Extreme Rain Event Presentation by Lance Wood My house Image Courtesy: Galveston Daily News Friendswood, TX Taylor Lake Village, TX

  2. The April 18th 2009 Extreme Rain Event 19 Z

  3. The April 18th 2009 Extreme Rain Event 24 Hour Rainfall

  4. 24 hr Rainfall Amounts 10 inches

  5. The April 18th 2009 Extreme Rain Event • A couple quick facts about this unique April rain event : • Recorded the highest recorded local rainfall rates with the greatest 1 hour rainfall rate. • A tipping bucket gauge on Clear Creek (@Bay Area Blvd) reported a • 6.9 inchhourly rainfall rate • -This was a higher rate than during TS Allison! • When compared to somewhat similar heavy rain events, this event stands out with its impressive 1, 3, and 6 hourly rain fall rates.

  6. 18 April 2009 Synoptic Overview • Upper divergence apparent at 300 mb level with SE Texas between two diverging jet streaks. • 500 mb low moving over the southern plains with a shortwave trough moving across SE Texas. • Deep layer moisture in the lower levels noticed at the 850 and 700 mb levels (PWATS : ~1.70” upper 25th %). • Pre-existing surface trough over the Houston area with a dry line and cold front approaching from the west.

  7. 18 April 2009 Synoptic Overviewcourtesy of http://www.spc.noaa.gov/obswx/maps/ 12 UTC 18 April 2009 00 UTC 19 April 2009 300 mb

  8. 18 April 2009 Synoptic Overviewcourtesy of http://www.spc.noaa.gov/obswx/maps/ 12 UTC 18 April 2009 00 UTC 19 April 2009 500 mb

  9. 18 April 2009 Synoptic Overviewcourtesy of http://www.spc.noaa.gov/obswx/maps/ 12 UTC 18 April 2009 00 UTC 19 April 2009 850 mb

  10. 18 April 2009 Synoptic Overviewcourtesy of http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml 18 UTC 18 Apr 2009 21 UTC 18 Apr 2009 00 UTC 19 Apr 2009 Surface plot/fronts/pressure

  11. The April 18th 2009 Extreme Rain Event 0Z 568 dam thickness  1.15” PWAT(70% saturation)Within a climatologically very saturated air mass (~ 1.70”) 70% Saturation Thickness (Funk 1991)

  12. Meso-Low Development L 1829 Z 1902 Z L 1930 Z 1956 Z L L

  13. The April 18th 2009 Extreme Rain Event West Galveston Bay Wind (6 minute data) Max wind = 52 kt wind gust Nearly an hour of sustained gale force winds

  14. The April 18th 2009 Extreme Rain Event West Galveston Bay Pressure (6 minute data) Min pressure = 1004.7 mb 11 mb drop in 4 hours

  15. Rain Gauge Limitations Tipping bucket: Can not keep pace with intense rainfall Loss of rain during bucket tips (1/2 sec) Can not be calibrated for 0.01 precision at high rainfall rates. • Expect a 20% loss during convective rainfall: • A 1.4” error for a near 7” rainfall total • *Greater error likely in high winds

  16. Rainfall Rate Comparisons / Impacts

  17. Short term Rainfall Rates ( Extremes ) 1 minute : 0.71” (Willow Spring @ Fairmont Parkway)* 15 minute : 2.44” (Clear Creek @ I-45) 30 minute : 4.22” (Clear Creek @ Bay Area Blvd) *{U.S. record = 1.23” Unionville, MD}

  18. Thank you! Questions? Acknowledgments Mr. Patrick Blood (NWS) Mr. Jeffery Lindner (Harris County Flood Control District) Mr. Scott Overpeck (NWS) Mr. Paul Lewis (NWS) Mr. Chris McKinney (NWS)

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