Radar – Supercell Convection Conceptual Models

1. Radar – Supercell Convection Conceptual Models

2. Supercells

4. Well developed Supercell with Rear Anvil

5. MAMMATUS CLOUDS (in the overhanging anvil)

6. MAMMATUS HEAVYRAIN RAIN HAIL SHORT FLANKING TOWERS (no rain) RAIN FREE BASE OVERSHOOTING TOPS

7. Banding

8. Wall Cloud Tail Cloud

10. Supercell Identification • Cloud Features

11. LP Supercell • Less common supercell

12. HP Supercell • More common supercell

13. Supercell Modeling - Satellite Features - Low Level Flow Boundaries • Outflow boundary interaction...

14. Supercell Modeling - Satellite FeaturesMid Level Flows relating to Low Level Flows • V- notch and other flows...

15. Storm Propagation • Regeneration • Propagation • Train-echo systems

16. Supercell Splitting - One • Storm splitting in straight line shear

17. Supercell Splitting - Two • Low level baroclinicity increases mid level meso

18. Supercell Splitting - Three • Veering hodo favours the right mover...

19. Supercell Splitting - Four • straight line shear • cyclonic shear with height

20. Supercell Structure • Potential satellite and radar clues to a supercell

21. Supercell Prediction

22. Instability • Thermodynamic parameters • The most important include: • CAPE • LI • Cap • Dewpoint depression 700 through 500 mb

23. Moisture - Dewpoints • Greater than 24C (75F) Incredibly juicy • 18-23C (65-74F) Juicy • 12-17C (55-64F) Semi-juicy • Less than 11C (55F) Low moisture content

24. Conceptual Model for Supercell Tornadogenesis

25. Shear • Positive shear in the 0 to 3km above ground level. Units are in time to the negative 1. • 0 to 3 weak • 4 to 5 moderate • 6 to 8 large • 9+ very large

26. Speed Shear • Causes updrafts to tilt in the vertical thus leading to supercell storms. • Speed shear also causes tubes of horizontal vorticity, which can be ingested into thunderstorms.

27. Cell Splitting

28. 0-3km VWS • Directional Shear • Cause horizontal vorticity • Also produces differential advection • Best case… SE at sfc… SW at 700 mb

29. Right Propagating Supercells

30. Tornadogenesis and the RFD

31. Storm-Relative 500 mb Winds • 500 mb level) storm-relative (S-R) winds useful to help differentiate between tornadic and non-tornadic supercells within the overall environment • Balance between Low-Level Inflow and • Low-level Rear Flank Downdraft

32. Storm-Relative 500 mb Winds • 500 mb S-R winds = 16 kts (8 m/s) Lower limit for tornadic supercells. • 500 mb S-R winds = 40 kts (20 m/s) Aprx upper limit for tornadic supercells.

33. Vorticity Generation • Advection + Tilting + Stretching • Stretching term is the ONLY term capable of amplifying vorticity to tornadic magnitudes

34. 500 millibar vorticity • Vorticity is a function of curvature, earth vorticity, and speed gradients. • If the values of vorticity are being rapidly advected, divergence will "in the real world" be much more than if the winds through the vorticity maximum are stationary or moving slowly.

35. Low Level Jet - LLJ • Strong low level winds will quickly advect warm and moist air into a region if it is associated with the low level jet • Low level convergence along LLJ

36. Upper level Jet Stream • Greater 200 knots Incredible divergence • 150 to 200 knots Large divergence • 100 to 149 knots Good divergence • 70 to 99 knots Marginal divergence • Less 70 knots Small divergence

37. Lake Breeze Boundaries – Guelph Tornado

38. Maximum Updraft Speed • W-max = square root of [2(CAPE)] • CAPE of 1500-2500 J/kg gives a w-max range of about 50-70 m/s (100-140 kts). • due to water loading, mixing, entrainment, and evaporative cooling, the actual w-max is approximately one-half that calculated

39. CAPE Distribution • A longer, narrower profile represents the potential for a slower updraft acceleration but taller thunderstorms which is best for high precipitation efficiency • A shorter, fatter profile would lead to a more rapid vertical acceleration which would be important for potential development of updraft rotation within the storm.

40. Convective Inhibition - CINH • negative area on a sounding. A large cap or a dry planetary boundary layer will lead to high values of CINH and stability

41. CAP • Cap strength in degrees Celsius • Cap needs to be less than 2 in general before it can be broken

42. Mesocyclone and the Updraft

43. RFD • If RFD is too cold and strong then the updraft may be undercut before tornadogenesis can begin • If the RFD is relatively warm, the tornadoes can be long lived and violent.

44. Precipitation Drag RFD’s • In moist thermodynamic profiles, evaporative cooling potential minimal even if heavy PCPN is close to the updraft… precipitation drag may drive the RFD.

45. Cyclic Mesocyclones

46. Tornado Events • Likely isolated supercells but can develop within line segments • High Ambient SRH (0-2km>200 m2s2) except when high CAPE and deviant storm motion locally creates helicity • Mid-upper level winds (4-6km >15kts) aid tornado development and longevity • CAPE/CAPE Distribution/LFC/LCL and Evaporative cooling (RFD) • Boundaries – local helicity and possibly lower LCL

47. Discrete Supercells • Convergence more localized than linear • If CIN/CAP weak, convergence trigger can be very subtle • Strong CIN/CAP (50 J/kg) under strong convergence • Shear is through a deep layer (0-6km) • Mean Shear Vector oriented at a relatively large angle to the initiating boundary • Discrete Supercells can evolve into lines but rarely from lines to discrete

48. LFC/LCL Heights • For greater tornado threat, relatively low LCL heights (<6000 ft) • High LCL heights associated with dry boundary layers promote • Convective downbursts • Outflow dominated convection

49. Horizontal Convective Rolls • Align with the mean wind • Forced by surface heating • Identified by cloud streets • Contribute to convection initiation

50. Horizontal Roll Conceptual Model