COMET FACULTY COURSE — JUNE 2000

1. COMET FACULTY COURSE — JUNE 2000 The Dallas and Fort Worth Storms of May 5, 1995 FROM: The University of Oklahoma, Dr. Ken Crawford and 7 Senior-Level Students in Meteorology [Fall 1999]

2. Synoptic Overview of the Dallas and Fort Worth Storms of May 5, 1995

3. 850 mb Heights and Observations

4. Strong Flow from the Gulf, Bringing in Moisture at 850mb 850 mb Heights and Observations

5. 10°-16°C Dew Points at 850mb 850 mb Dew point Temperatures

6. L 5:00 p.m. Surface Analysis

7. 12Z May 5 00Z May 6 Soundings from DFW

8. Lifted Indices at 00Z May 6

9. Precipitable Water at 00Z May 6

10. • 250 mb diffluent flow Composite Map

11. • 250 mb diffluent flow • 500 mb shortwave Composite Map

12. • 250 mb diffluent flow • 500 mb shortwave • 850 mb dew point temperatures 10° - 16° C Composite Map

13. • 250 mb diffluent flow • 500 mb shortwave • 850 mb dew point temperatures • low-level jet Composite Map

14. • 250 mb diffluent flow • 500 mb shortwave • 850 mb dew point temperatures • low-level jet • stationary front Composite Map

15. • 250 mb diffluent flow • 500 mb shortwave • 850 mb dew point temperatures • low-level jet • stationary front • precipitable water values from 1.5-2.0 inches Composite Map

16. Radar Summary of the Dallas and Fort Worth Storms of May 5, 1995

17. Parker Co. Tarrant Co. Dallas Co. Base Reflectivity Loop from 6:04 p.m. to 8:59 p.m.

18. • 6:00 p.m DFW RADAR • Supercell located in SW Parker County • Squall line extends from Young to Eastern County • Reflectivity max at 60 dBz’s • Golfball sized hail now 18” deep in southern Parker County

19. • 6:00 p.m. DFW radar • South to North cross section • Bounded Weak Echo Region • Hail Core • Reflectivity max at 60 dBz’s Base Reflectivity Cross Section

20. • 6:45 p.m. DFW radar • Supercell located in SE Parker County about to enter FTW metro • Squall line beginning to bow west of the supercell • Max Reflectivity of 75 dBz’s • Grapefruit-sized hail about to occur in Tarrant County

21. • 6:45 p.m. DFW radar • South to North cross section • More pronounced Bounded Weak Echo Region • Hail Core • Reflectivity max at 75 dBz’s Base Reflectivity Cross Section

22. strong meso • 6:45 p.m. DFW radar • Base Velocity product • Strongest meso WNW of radar site

23. • 6:45 p.m. DFW radar • West to East cross section • Meso evident within the Super- cell • Isentropic lift Base Velocity Cross Section

24. • 7:30 p.m. DFW radar • Supercell located in Tarrant County • Time of largest hail [grapefruit sized] • Supercell is caught by the squall line • Max Reflectivity of 67 dBz’s

25. • 7:45 p.m. DFW radar • South to North cross section • Hail Core lessening • Lower dBz’s aloft • Reflectivity max at 67 dBz’s • 17 people about to drown in Dallas Base Reflectivity Cross Section

26. • 8:00 p.m. DFW radar • Heavy precip threat beginning • Supercell is consumed by the squall line • Large area of reflectivity greater than 50 dBz

27. • 8:00 p.m. DFW radar • West to East cross section • Strong uplifting within the squall- line. Base Velocity Cross Section

28. Approx. 3 inches of rain in one hour One Hour Precip from 8:00 to 9:00 p.m.

29. One Hour Precip Loop from 8:04 to 8:50 p.m.

30. • 9:00 p.m. DFW radar • South to North cross section • Very low dBz’s aloft • Reflectivity max at 55 dBz’s Base Reflectivity Cross Section

31. 3.5 + inches of rain • 9:00 p.m. total precip image • Areas received over 3.5 inches of rain

32. • 7:30 p.m radar image • Time of largest hail [grapeftuit sized] • Strong bow in squall line approaching supercell

33. Heavy Rains Inflow Notch

34. 9:10 p.m. Reflectivity Image

35. OFFICIAL HAIL DAMAGE • 80+ REPORTS OF 1” OR SMALLER HAIL • 8 REPORTS OF 2” - 3” HAIL • 3 REPORTS OF 4” HAIL • 90 INJURIES ASSOCIATED WITH HAIL • DAMAGE TO BUILDINGS.

36. FLASH FLOODING • LARGEST CONTRIBUTOR TO FATALITIES • 15 MINUTE RAINFALL AMOUNTS VARYING FROM 1.58” TO 2.24” IN DALLAS METRO AREA • INSUFFICIENT DRAINAGE FOR RAINFALL RATE

37. WIND DAMAGE • SEVERAL REPORTS IN EXCESS OF 70 MPH • WALL OF LOCAL WAREHOUSE BLOWN IN

38. MAY 5 - 6 FATALITIES • 20 DEATHS TOTAL • 4 FATALITIES FROM VICTIMS DRIVING INTO HIGH WATER • 2 FATALITIES WHEN ROOF COLLAPSES • 1 VICTIM STRUCK BY LIGHTNING • 3 VICTIMS PULLED INTO DRAINAGE SYSTEM

39. AN OUNCE OF PREVENTION • 60 - 70 OF HAIL INJURIES OCCURRED AT MAYFEST • MAYFEST OFFICIALS DID NOT CONTACT NWS FOR WEATHER REPORT PRIOR TO EVENT • “WARNINGS WERE ISSUED NEARLY 25 TO 30 MINUTES” PRIOR TO STORM HITTING MAYFEST

40. Questions? You’re not the only one!

41. A Few Bullets Related to the Learning Objectives: This event had the synoptic scale appearance of a severe weather outbreak with relatively fast moving storms. However, the strong digging trough into a negatively tilted ridge in the upper levels, and a very notable northward transport of moisture in the lower levels suggested the potential for heavy precipitation. Large scale jet dynamics [divergence/diffluence over Texas] supported upward motion. In the low levels, surface boundaries associated with a warm front and with a mesohigh that developed became the focus of low-level convergence and enhanced upward motion. This was especially true of the east-west warm frontal boundary that was roughly perpendicular to the 850 mb flow. Such a configuration lead to a common generation point.

42. A Few Bullets Related to the Learning Objectives: By the beginning of this event, conditions suggested enhanced duration was possible where the low-level flow intersected surface boundaries. But rainfall intensity and hydrologic character of the basin were more important in this event. Although large amounts of hail occurred throughout much of the storm history, a transformation into a more intense rainstorm occurred in Dallas County. This evolution can be seen in the change of characteristics of the radar echo. The low-level moisture transport was very strong, and when coupled with vertical motion, may have increased the height of the freezing level. The result was a deeper warm cloud layer and thus more efficient precipitation processes.

43. A Few Bullets Related to the Learning Objectives: The hydrologic response in this highly urbanized area was very rapid due to the impermeable surfaces and constricted waterways. Even though a second heavy accumulation band can be noted south of the Dallas rainfall footprint, serious flooding did not occur there [primarily] because the rainfall intensity and urban runoff characteristics were so different from that in Dallas. The final rainfall amounts were not very impressive by Texas standards. The intensity of the precipitation and the hydrologic response of the urbanized environment contributed greatly to this deadly flash flood event. Rainfall amounts up to 4.75 inches were reported in Dallas, but rainfall rates for short periods approached 10 inches per hour.

44. The Financial Toll: Estimated damages across Parker, Tarrant and Dallas counties — from this storm — was estimated at over $1.2 Billion — the costliest thunderstorm event in the history of the USA.