Warm-Season Elevated Thunderstorms with Heavy Rainfall: A Composite Study

1. Warm-Season Elevated Thunderstorms with Heavy Rainfall: A Composite Study Dr. Scott M. Rochette SUNY Brockport

2. Basis of Presentation • Background Review • Methodology of Composite Study • Kinematic and Thermodynamic Fields • Stability and Moisture Fields • Vertical Profiles and Hodographs • Correlations • Conceptual Model • Summary

3. Background Review

4. Elevated Thunderstorms 1(Colman 1990) • An elevated thunderstorm occurs above a frontal inversion • Isolated from surface diabatic effects • Colman’s criteria • observation must lie on the cold side of an analyzed front, showing a clear contrast in temperature, dew point, and wind • station’s temperature, dew point, and wind must be qualitatively similar to immediately surrounding values • surface air on warm side of analyzed front must have higher e than air on cold side

5. Elevated Thunderstorms 2(Colman 1990) • Cold-sector MCSs generally fit Maddox frontal or meso-high type flash flood scenarios • Elevated thunderstorms can occur during any time of year • usually associated with heavy rain/snow or hail • nearly all winter-season thunderstorms over the U.S. east of the Rockies (excluding Florida) are elevated

6. Elevated Thunderstorm Climatology 1 • Climatology of elevated thunderstorms reveals bimodal variation • primary maximum in April • secondary maximum in September (Colman 1990)

7. Elevated Thunderstorm Climatology 2 (Colman 1990)

8. Elevated Thunderstorm Climatology 3 (Colman 1990)

9. Max-e CAPE Use max-e CAPE when lifting is at/above frontal zone (stable PBL)

10. Elevated Convective Instability 1 • Convectively stable PBL • eincreases w/height • Convective environment insulated from local surface diabatic effects • Convective instability above frontal zone • edecreases w/height • Vertical profile helpful for diagnosis

11. Elevated Convective Instability 2 (Trier and Parsons 1993)

12. Methodology

13. Composite Study of WSElevated Thunderstorms 1 • 21 Cases • 35 Events • Some occurred over multiple time periods •  4 in (24 h)-1 of rain over  (100 km x 100 km) area • Diagnostic fields computed for each event • Thermodynamic • Kinematic • Stability • Moisture • Pre-convective environment ( 4 h of 0000/1200 UTC)

14. Composite Study of WSElevated Thunderstorms 2 • MCS centroid identified for each event • Initiation point • Point of most intense convection • 11 x 11 grid defined wrt centroid • x = 190.5 km • Grid computed for each parameter/event • Composite fields created by averaging objectively analyzed fields for individual parameters • Storm-relative composites • Geography shows spatial orientation/relative magnitudes • Not meant to signify specific geographic location

15. Elevated Thunderstorm Distribution (1993-1998)

16. Elevated +TSRA Events 1993-1998

17. MCS Centroid Locations

18. Kinematic and Thermodynamic Fields

19. Composite Surface Conditions

20. Composite 925-hPa h/T

21. Composite 925-hPa Winds

22. Composite 925-hPa e

23. Composite 925-hPa Moisture Convergence

24. Composite 850-hPa h/T

25. Composite 850-hPa Winds

26. Composite 850-hPa e

27. Composite 850-hPa -V•e

28. Composite 850-hPa -•(qV)

29. Composite 850-hPa w

30. Composite 850-hPa qV

31. Composite 850-hPa -V•T

32. 925- & 850-hPa Proximity Frontogenesis

33. Composite 700-hPa Winds

34. Composite 700-hPa T

35. Composite 700-hPa -V•T

36. Composite 700-hPa -•(qV)

37. Composite 500-hPa Winds

38. Composite 500-hPa h/

39. Composite 250-hPa Winds

40. Composite 250-hPa •V

41. Stability and Moisture Fields

42. Composite Lifted Index

43. Composite Showalter Index

44. Composite Mean-Parcel CAPE

45. Composite Mean-Parcel CIN

46. Composite Max-e CAPE

47. Composite Max-eCIN

48. Composite Convective Instability (e850 - e500)

49. Composite K Index

50. Composite Precipitable Water