1. Title card A Look at Environments Associated with Nighttime Supercell Tornadoes in the Central Plains Meteorologist Jon Davies Private © Dick McGowan & Darin Brunin

2. Processes Basic parameters that suggest potential for strong tornadic supercell storms: CAPE – buoyancy/instability for thunderstorm updrafts SRH (storm-relative helicity) – change in wind direction and increase in wind speed not far above ground as a source of “spin” or rotation in low-levels Deep layer shear – increasing winds with height through a deep layer to organize and strengthen updrafts CAPE in low-levels near the ground (0-3 km CAPE) and low cloud bases (LCL heights) for storms that are strongly surface-based without excessive cold outflow

3. If air bubbles near ground don’t have to be lifted very far to become buoyant and rise on their own, developing low-level circulations can stretch and spin faster Low-level CAPE and a strongly surface-based environment probably help with stretching at the ground. stretching at ground

4. If air bubbles near ground are too cool, it’s like the updraft has to lift bricks instead of ping-pong balls near the ground Cool, stable air in low-levels tends to reduce stretching at the ground, though there may be CAPE further above. stretching aloft Layer of cool, stable air

5. Stats noon 6 pm mid 6 am noon 6 pm mid 6 am North Dakota tornadoes 1950-1989 Mississippi tornadoes 1950-1989 Tornadoes by time of day (from Grazulis ) 100 80 60 40 20 75 50 25

6. MLCAPE 2050 J/kg 0-1k SRH 143 m /s 0-1k EHI 1.8 0-6k shear 58 kts MLLCL 1200 m MLCIN –55 J/kg 2 2 weak inversion RUC analysis

7. MLCAPE 2165 J/kg 0-1k SRH 357 m /s 0-1k EHI 4.8 0-6k shear 55 kts MLLCL 500 m MLCIN –150 J/kg 2 2 strong inversion only 2 hours later! Tornado warned supercell near Dodge City after dark, no tornadoes surface cooling RUC analysis

8. MLCAPE 960 J/kg 0-1k SRH 370 m /s 0-1k EHI 2.2 0-6k shear 52 kts MLLCL 700 m MLCIN –15 J/kg 2 2 little or no inversion Nighttime killer tornado at Evansville IN 22 dead middle of the night! RUC analysis

9. Key characteristics – plains vs. eastern U.S. A key difference between environments in the Great Plains and areas farther east (Gulf Coast-Ohio Valley) that impacts the occurrence of nighttime tornadoes: An elevated mixed layer from the dry desert southwest is often present in the plains. Cooling at nightfall beneath this layer can rapidly change a strongly surface-based environment to one that is more elevated and not really surface-based, reducing the chance of nighttime tornadoes. In the eastern U. S., the absence of this elevated mixed layer when strong low-level moist advection is taking place often makes for a better chance of tornadoes at night.

10. A typical nighttime evolution of parameters in the plains… Typical nighttime evolution of parameters in the plains…

11. SRH 0-1 km SRH NAM/WRF model

12. 0-1 km SRH Low-level shear increases with nocturnal backing of winds and the nocturnal increase in the low-level jet NAM/WRF model

13. 0-1 km SRH Low-level shear increases with nocturnal backing of winds and the nocturnal increase in the low-level jet NAM/WRF model

14. EHI 0-1 km EHI NAM/WRF model

15. 0-1 km EHI The resulting rise in SRH increases nighttime CAPE-shear combinations NAM/WRF model

16. 0-1 km EHI The resulting rise in SRH increases nighttime CAPE-shear combinations NAM/WRF model

17. Low-level CAPE 0-3 km CAPE NAM/WRF model

18. 0-3 km CAPE BUT… nocturnal cooling decreases low-level CAPE, causing nighttime environments to become increasingly “elevated” NAM/WRF model

19. 0-3 km CAPE BUT… nocturnal cooling decreases low-level CAPE, causing nighttime environments to become increasingly “elevated” NAM/WRF model

20. Characteristics to watch for… Nighttime situations to watch for in the Central Plains are those where the elevated mixed layer and accompanying inversion are not particularly strong, and where strong warm-moist advection is taking place to reduce the impact of nighttime cooling.

21. Model forecast characteristics that can help with assessing nighttime environments more conducive to tornadoes after dark in the Central Plains: Strong CAPE-shear combinations at night The presence of significant low-level CAPE (CAPE below 3 km) at night, suggesting strong warm-moist advection and a more surface-based environment

22. Some case studies… Case studies…

23. 28 Feb 2007 KS-MO tornadic supercell 28 February 2007

27. Tornadic supercell east-central Kansas 7:30-8:00 p.m. CST (in late February!)

28. © Andy Fischer © courtesy KMBC-TV EF-4 tornado after dark in Linn County, KS 2/28/07

29. Tornadoes continued into Missouri after 10 p.m. CST

30. 0245 UTC

31. MLCAPE 870 J/kg 0-1k SRH 460 m /s 0-1k EHI 2.5 0-6k shear 56 kts MLLCL 930 m MLCIN –55 J/kg 2 2 weak inversion RUC analysis

32. MLCAPE 620 J/kg 0-1k SRH 280 m /s 0-1k EHI 1.1 0-6k shear 53 kts MLLCL 1050 m MLCIN –30 J/kg 2 2 little or no inversion WRF 3 hr forecast for CNU valid 03 UTC

33. 17 April 2004 N Iowa nontornadic supercells 17 April 2004

36. Poor low-level CAPE indicated

37. Strong supercells after dark in northern Iowa

38. Isolated wind damage, but no tornadoes

39. 0245 UTC

40. MLCAPE 1030 J/kg 0-1k SRH 480 m /s 0-1k EHI 3.1 0-6k shear 60 kts MLLCL 970 m MLCIN –210 J/kg 2 2 strong inversion RUC analysis

41. 4 May 2007 Greensburg tornado 4 May 2007 Greensburg event

47. 0145 UTC

50. © Dick McGowan & Darin Brunin © Courtesy Wichita Eagle EF-5 tornado strikes Greensburg KS before 10 p.m. CDT 5/4/07

51. Tornadoes continued in central Kansas well after midnight!

52. MLCAPE 1600 J/kg 0-1k SRH 205 m /s 0-1k EHI 2.0 0-6k shear 46 kts MLLCL 1640 m MLCIN –190 J/kg 2 2 strong inversion RUC analysis Erroneous moisture! (too dry in low-levels)

53. MLCAPE 3800 J/kg 0-1k SRH 240 m /s 0-1k EHI 5.6 0-6k shear 47 kts MLLCL 710 m MLCIN –10 J/kg 2 2 weak inversion WRF 3 hr forecast for PTT valid 03 UTC Much better depiction of low-level moisture!

54. MLCAPE 3800 J/kg 0-1k SRH 240 m /s 0-1k EHI 5.6 0-6k shear 47 kts MLLCL 710 m MLCIN –10 J/kg 2 2 WRF 3 hr forecast for PTT valid 03 UTC Much better depiction of low-level moisture! hodograph

55. Greensburg KS (EF-5) Moore OK (F5) from Johns & Davies 1993

56. Quick review of the cases we just looked at… Review

57. 28 Feb 2007

59. significant tornadoes well after dark (significant low-level CAPE)

60. 17 April 2004

62. no tornadoes after dark (no low-level CAPE – elevated storms) 17 April 2004

63. 4 May 2007

65. strong-violent tornadoes well into the night (plentiful low-level CAPE)

66. Summary Regarding potential for strong or violent tornadoes after dark, on forecast models such as the WRF, watch for: Strong CAPE-shear combinations after dark Significant low-level CAPE continuing after dark

67. RUC caveats Beware the RUC! It is often too dry in low-levels with strong moisture advection situations such as: Retreating (westward moving) drylines Advancing warm fronts The WRF seems to handle these situations better.

68. Close © Jon Davies My site (Greensburg tornado case study): http://members.cox.net/jdavies1 Earl Barker’s site: www.wxcaster.com

69. © Jon Davies My site (Greensburg tornado case study): http://members.cox.net/jdavies1 Earl Barker’s site: www.wxcaster.com I’ve moved! Jon Davies 9101 Alpha Ridge Rd. Trimble MO 64492 (north of Kansas City) e-mail remains for now: jdavies1@cox.net

70. Book

76. F-4

77. Available from www.amazon.com (search on “Jon Davies”) and www.farcountrypress.com

78. Close © Jon Davies My site (Greensburg tornado case study): http://members.cox.net/jdavies1 Earl Barker’s site: www.wxcaster.com New address: Jon Davies 9101 Alpha Ridge Rd. Trimble MO 64492 (north of Kansas City) e-mail remains for now: jdavies1@cox.net