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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
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.


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


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



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


Accumulated Rainfall ( Period Ending 1200 UTC 7 May 2000Grey) 30 Minute Rainfall (Blue)


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


Flat Creek Watershed – Union, MO time period 04 UTC to 11 UTC 7 May 2000


Surface Analysis Valid 04 UTC 7 May 2000 time period 04 UTC to 11 UTC 7 May 2000


Surface Analysis Valid 06 UTC 7 May 2000 time period 04 UTC to 11 UTC 7 May 2000


Surface Analysis Valid 08 UTC 7 May 2000 time period 04 UTC to 11 UTC 7 May 2000


Surface Analysis Valid 10 UTC 7 May 2000 time period 04 UTC to 11 UTC 7 May 2000


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


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


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


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


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


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


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


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


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


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


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

B

A


KLSX WSR-88D Cross-Section Valid 0415 UTC to 0831 UTC 7 May 2000

A

B


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

A

B

B


KLSX WSR-88D Cross-Section Valid 0731 UTC to 1100 UTC 7 May 2000

A

B



  • Diagnostic View of the Propagation Vectors UTC 7 May 2000

  • 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



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



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)



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


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


Modification to the vector approach
Modification to the “Vector Approach” 0500-1100 UTC 7 May 2000

  • 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


  • CONCLUSIONS 0500-1100 UTC 7 May 2000

  • 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.


  • CONCLUSIONS (cont.) 0500-1100 UTC 7 May 2000

  • 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


  • CONCLUSIONS (cont.) 0500-1100 UTC 7 May 2000

  • 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)


Conclusions cont
CONCLUSIONS (cont.) 0500-1100 UTC 7 May 2000

  • 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)


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:

[email protected]


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