The Extreme East-Central Missouri Flash Flood of 6-7 May 2000 James T. Moore, John P. Gagan

The Extreme East-Central Missouri Flash Flood of 6-7 May 2000

James T. Moore, John P. Gagan

Cooperative Institute for Precipitation Systems

Department of Earth and Atmospheric Sciences

Saint Louis University

and Fred H. Glass

NWSFO St. Charles, MO

Hydrometeorology Course for RFC/HPCFriday, 8 December 2000

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.

Flat Creek Watershed – Union, MO

Infrared Satellite Imagery Valid 1815 UTC 5 May 2000 to 1815 UTC 6 May 2000

NIDS Radar Imagery Valid 0134 to 1800 UTC 6 May 2000 http://www.rap.ucar.edu/staff/pneilley/NIDS_archives.html

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

2000

Accumulated Rainfall (Grey) 30 Minute Rainfall (Blue)

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

UTC 7 May 2000

Pre-storm Environment

• Weakening mid-level cyclonic vortex (MCV) with warm core characteristics moving northeasterly from northeast Oklahoma into central Missouri.

• Very moist tropospheric conditions:

• 1000-500 mb mean relative humidity values > 80%

• Lower tropospheric dewpoints in lower-middle teens ºC

• PWs of 1.19 - 1.47 inches (153-216%)

• warm cloud depths ranged from 3.1 –3.3 km

• Weak instability with CAPEs between 500-1000 J kg-1

• Weak vertical wind shear in the mid-upper levels

• Strong Low-Level Jet (LLJ) from the south-southwest (at times exceeding 50 knots)

925 mb surface 7 May 2000 00 UTC

---- Isodrosotherms


---- Isodrosotherms


--- Isotachs


--- Isotachs


--- Isotherms


--- Isotherms


--- Isotachs


--- Isotachs

THE EVENT

•A mesoscale convective system (MCS) formed near the center of the MCV and created an outflow boundary at the surface

•This outflow boundary was weak, due to the very moist atmosphere in which it formed, and moved very little during the nighttime hours of 7 May 2000

•The southwesterly LLJ was strong and wide. It flowed nearly perpendicular to the outflow boundary, veering as time progressed, and acted as a focusing mechanism for convection

THE EVENT (cont.)

•The steering flow (from 700 mb to 300 mb) was predominantly westerly, veering as time progressed, and was oriented parallel to the outflow boundary

•The nature of the training changed with time from west-east to northwest-southeast in concert with a change in cell motion

•This change in cell motion was related to veering of the cloud-layer wind

Surface Analysis Valid 00 UTC 7 May 2000

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12 1213

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Surface e for 06 UTC 7 May 2000





RUC Initialization Composite Chart Valid 12 UTC 6 May 2000

Precipitable Water (1.2 inches) 1000-500mb Mean RH (%)

K-Index (28)



K-Index (28)



K-Index (28)

Springfield, MO (SGF) Skew-T Valid 00 UTC 7 May 2000

wcd = 3.02 km

Springfield, MO (SGF) Skew-T Valid 12 UTC 7 May

2000 wcd = 3.27 km

Lincoln, IL (ILX) Skew-T Valid 00 UTC 7 May

2000wcd = 3.0 km

Lincoln, IL (ILX) Skew-T Valid 12 UTC 7 May 2000

wcd = 3.31 km

RUC Initialization 950 mb to 850 mb Layer-Averaged Wind Vectors and Isotachs Valid 00 UTC 7

May 2000


May 2000


May 2000


May 2000


May 2000

Vertical Wind Profile Display from the KLSX WSR-88D Valid 0600 UTC to

0700 UTC 7 May 2000


0800 UTC 7 May 2000


0900 UTC 7 May 2000


1000 UTC 7 May 2000


1100 UTC 7 May 2000

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

KLSX WSR-88D storm total precipitation estimate for 04 UTC to 11 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

AB

A B

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

May 2000

B

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

A

B

A B

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

May 2000

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

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

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

Prognostic Corfidi Vector Calculation Valid 05 UTC 7

May 2000

Vs

Vp

Vc

Propagation Vector Calculation

Vs

Vc Vp

Prognostic Corfidi Vector Calculation Valid 11 UTC 7

May 2000

Vs

Vp

Vc

Propagation Vector Calculation

Vs

Vp

Vc

Propagation Vector Loop Valid 05 UTC to 11 UTC 7 May

2000

How did the numerical models do?

We take a look at the 00 UTC run of the Eta for 7 May 2000

Eta-40 km 00 UTC 7 May 2000 Run QPF 00-06 UTC 7 May 2000



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.

CONCLUSIONS (cont.)

• The heavy rainfall event in MO was part of a cyclic heavy rainfall system associated with a mid-level, warm core vortex that developed from a cold core low.

• 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.) • 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.)

• 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 mesoscale 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]

The Extreme East-Central Missouri Flash Flood of 6-7 May 2000 James T. Moore, John P. Gagan

Documents

isodrosotherms925 mb

isodrosotherms850 mb

isotachs850 mb surface

isotachs500 mb surface

isotherms500 mb surface

isotherms250 mb surface

isotachs250 mb surface

surface e