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Extreme Heavy Rain in Franklin County, Missouri

Extreme Heavy Rain in Franklin County, Missouri. Occurred during the nighttime and early hours of 6-7 May 2000 Rainfall exceeding 4 inches (100 mm) fell over a 5500 km 2 area, with embedded amounts over 12 inches (300 mm)

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Extreme Heavy Rain in Franklin County, Missouri

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  1. Extreme Heavy Rain in Franklin County, Missouri • Occurred during the nighttime and early hours of 6-7 May 2000 • Rainfall exceeding 4 inches (100 mm) fell over a 5500 km2 area, with embedded amounts over 12 inches (300 mm) • There were two fatalities and property damage of over 100 million dollars • 379 structures damaged or destroyed in Franklin County; declared a disaster area by the President • Flat Creek in Franklin County rose about 15 feet (4.57 m) destroying two mobile home parks.

  2. GOES-8 Infrared Satellite Loop Valid 1815 UTC 6 May 2000 to 1815 UTC 7 May 2000

  3. KLSX WSR-88D Reflectivity Loop (dBZ) Valid 0415 UTC to 1100 UTC 7 May 2000

  4. KLSX WSR-88D storm total precipitation estimate for 04 UTC to 11 UTC 7 May 2000

  5. 24-Hour Precipitation Analysis for the Period Ending 1200 UTC 7 May 2000

  6. Accumulated Rainfall (Grey) 30 Minute Rainfall (Blue)

  7. Loop of one-hour KLSX WSR-88D rainfall estimation for the time period 04 UTC to 11 UTC 7 May 2000

  8. Flat Creek Watershed – Union, MO

  9. Surface Analysis Valid 04 UTC 7 May 2000

  10. Surface Analysis Valid 06 UTC 7 May 2000

  11. Surface Analysis Valid 08 UTC 7 May 2000

  12. Surface Analysis Valid 10 UTC 7 May 2000

  13. RUC Initialization 950 mb to 850 mb Layer-Averaged Wind Vectors and Isotachs Valid 06 UTC 7 May 2000

  14. RUC Initialization 950 mb to 850 mb Layer-Averaged Wind Vectors and Isotachs Valid 09 UTC 7 May 2000

  15. RUC Initialization 950 mb to 850 mb Layer-Averaged Wind Vectors and Isotachs Valid 12 UTC 7 May 2000

  16. Vertical Wind Profile Display from the KLSX WSR-88D Valid 0400 UTC to 0500 UTC 7 May 2000

  17. Vertical Wind Profile Display from the KLSX WSR-88D Valid 0500 UTC to 0600 UTC 7 May 2000

  18. Vertical Wind Profile Display from the KLSX WSR-88D Valid 0600 UTC to 0700 UTC 7 May 2000

  19. Vertical Wind Profile Display from the KLSX WSR-88D Valid 0700 UTC to 0800 UTC 7 May 2000

  20. Vertical Wind Profile Display from the KLSX WSR-88D Valid 0800 UTC to 0900 UTC 7 May 2000

  21. Vertical Wind Profile Display from the KLSX WSR-88D Valid 0900 UTC to 1000 UTC 7 May 2000

  22. Vertical Wind Profile Display from the KLSX WSR-88D Valid 1000 UTC to 1100 UTC 7 May 2000

  23. KLSX WSR-88D plane view of the cross-section of reflectivity (dBZ) from 0415 UTC to 0831 UTC 7 May 2000 B A

  24. KLSX WSR-88D Cross-Section Valid 0415 UTC to 0831 UTC 7 May 2000 A B

  25. KLSX WSR-88D plane view of the cross-section of reflectivity (dBZ) from 0730 UTC to 1100 UTC 7 May 2000 A B B

  26. KLSX WSR-88D Cross-Section Valid 0731 UTC to 1100 UTC 7 May 2000 A B

  27. KLSX WSR-88D Storm Relative Velocity Valid 0415 UTC to 1100 UTC 7 May 2000

  28. Diagnostic View of the Propagation Vectors • Prognostic storm-motion vectors are calculated using the LLJ and mean 850-300 mb wind vectors (Corfidi 1996) • In this case, the prognostic vectors that were calculated gave an erroneous system-motion speed and direction because they relied solely on the LLJ • “True” propagation vectors were calculated using the satellite-derived system motion and radar-derived cell motion vectors to obtain the actual nature of the propagation • The finding that propagation is influenced by more than the LLJ is consistent with earlier work by Moore et al. (1993) and Corfidi (1998) • In this case, propagation appeared to be influenced by the outflow boundary, mesolow, and the LLJ

  29. Prognostic and Diagnostic Corfidi Vector Diagrams Valid 0500 UTC 7 May 2000 FORECAST ACTUAL

  30. 1000 – 900 mb Moisture Convergence Valid 0500 UTC 7 May 1999

  31. Prognostic and Diagnostic Corfidi Vector Diagrams Valid 0600 UTC 7 May 2000 FORECAST ACTUAL

  32. Propagation Composite Chart Valid 0600 UTC 7 May 2000 LLJ ULJ Moisture Convergence (gm kg-1 hr-1) 900-600 mb Convective Instability 900-800 mb Layer Average MTV (gm kg-1 m s-1)

  33. Prognostic and Diagnostic Corfidi Vector Diagrams Valid 1100 UTC 7 May 2000 FORECAST ACTUAL

  34. 1000 – 900 mb Moisture Convergence Valid 1100 UTC 7 May 1999

  35. Diagnostic Corfidi Vector Loop Valid 0500-1100 UTC 7 May 2000

  36. Modification to the “Vector Approach” • Corfidi (1998, SLS Preprint) has noted that the environments of back-building convection and bow echoes/derechoes often look similar – even though bow echoes are distinctly forward propagators • Forward propagation is favored by the presence of unsaturated air – either in the mid-levels or sub-cloud layer – ahead of the developing MCS. • Quasi-stationary/back-building MCSs are associated with more nearly saturated lower tropospheric environments. • It is the potential to produce strong downdrafts at the surface and therefore the formation of a strong mesohigh that distinguishes the bow echo/derecho environment from that more conducive to a back-building MCS. • The mesohigh helps maximize system-relative convergence downstream from the MCS

  37. CONCLUSIONS • The heavy rain event that occurred during the nighttime hours of 7 May 2000 was due to regenerative convection which resulted in a quasi-stationary MCS • Franklin County, MO was deluged with over 10 inches of rain in a six-hour period, with some portions of the county receiving 14-16 inches • Catastrophic flooding occurred along Flat Creek watershed which runs through the center of Union in Franklin County. Damage estimates exceeded $100 million.

  38. CONCLUSIONS (cont.) • The heavy rainfall event in MO was part of a cyclic heavy rainfall system associated with a mid-level, warm core vortex • As the convective system grew, a weak outflow boundary became aligned parallel to the upper-level flow and nearly normal to the LLJ • As the MCS matured, a weak surface mesolow formed upstream from the convection, further enhancing low-level convergence • Diagnostic calculations of the propagation vector revealed that the storm motion remained < 3.5 m s-1

  39. CONCLUSIONS (cont.) • Vector analysis further reveals that the propagation vector was opposite to the cell motion vector signaling a quasi-stationary MCS • The Corfidi Vector Method was inappropriate in this case as the storm-relative inflow was NOT solely a function of the LLJ • The heavy rain environment was characterized by: • weak mid-upper level wind shear • high mean surface-500 mb RH • deep warm cloud depths (~3.3 km) • PW values > 175% of normal (> 1.3 inches) • modest CAPE values (500-1000 J kg-1)

  40. CONCLUSIONS (cont.) • High e air (> 340 K) resided to the southwest of the MCS • The MCS formed downstream from a maxima in the 850 mb moisture transport vectors • The various Eta model QPFs were on the order on 0.5 inches for the 18 h period. • One would not expect numerical models to be able to handle this meso- scale heavy rain event – especially a hydrostatic model with an inability to simulate downdrafts (albeit weak ones)

  41. This presentation can be viewed and/or downloaded at the following web site: http://www.eas.slu.edu/CIPS/Presentations In addition, Fred Glass of the NWSFO in St. Charles, MO has written a preprint for the 81st Annual AMS meeting. To obtain a copy of this preprint email Fred at: Fred.Glass@noaa.gov

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