Severe Weather and Storm Chasing

1. April 10, 2012 Joe Halvorson, Chris MacIntosh, Tim Marquis Severe Weather and Storm Chasing

2. What causes a storm, severe parameters, tools. Severe Weather Basics.

3. The Basics • Thunderstorms need three things to develop: • Moisture • Instability • Lift/Trigger • Severe storms need one more ingredient: • Wind shear (directional, speed)

4. Storm Types • Single cell: “popcorn” storms • Usually not severe, short-lived • Multicell: group of cells moving together • Moderate severe, tornado potential • Squall line: line of storms • Moderate severe, low tornado potential • Supercell: storm with a rotating updraft (mesocyclone) • Very high severe potential • Main tornado producer

5. Singe cell

6. Multicell

7. Multicell radar 4 cells

8. Quasi-Linear Convective System (QLCS)

9. Supercell Structure

10. Supercell Structure

11. Parameters • CAPE/CIN(H) • Bulk Shear • Storm-Relative Helicity • Energy Helicity Index • Others • LCL Heights, LI, Lapse Rates. • Supercell Composite, Significant Tornado Parameter

12. CAPE • Convective Available Potential Energy • Ability that a parcel has to rise • Large CAPE usually means large vertical velocities • Different types: • Surface-based • Mixed-layer (Mean layer) • Most unstable • 0–3 km • “Skinny” and “Fat” CAPE • Skinny: weaker updrafts • Fat: stronger updrafts

13. “Fat” CAPE CAPE! “Skinny” CAPE CAPE!

14. CAPE • Thresholds (in J kg-1): • 1–1,000 : Marginally unstable • 1,000–2,500 : Moderately unstable • 2,500–3,500 : Very unstable • 3,500+ : Extremely unstable • For 0–3 km CAPE, 100+ J kg-1 best for tornadic environment

15. CIN (CINH) • Convective Inhibition • “Cap,” can prevent instability from being realized • Negative CAPE • Ways to overcome CIN: • Heating (daytime or warm air advection) • Moisture • Lift

16. CIN!

17. CIN (CINH) • Thresholds (in J kg-1): • 0–50 : Weak cap • 50–200 : Moderate cap • 200+ : Strong cap • These values are negative on most model and mesoanalysis charts.

18. CAPE/CIN: 24 May 2011 Surface-based Mixed-layer

19. Bulk Shear • Change in wind direction and speed with height put into a single number • Most useful: 0–1 km, Effective • Effective accounts for storm depth (inflow base to equilibrium level) • Thresholds • 0–1 km : 15-20+ kts supportive of tornadoes • Effective : 25–40+ kts supportive of supercells

20. Bulk Shear: 27 April 2011 Effective 0–1 km

21. Storm-Relative Helicity (SRH) • Measure of the potential for a rotating updraft in a supercell • Higher numbers associated with a higher potential for tornadoes • Three types: • 0–1 km, 0–3 km, effective • Effective is most useful in discriminating between tornadic and nontornadic storms.

22. Storm-Relative Helicity (SRH) • Thresholds (in m2 s-2) • 0–1 km : 100+ • 0–3 km : 250+ • Effective : 100+

23. 0–1 km SRH: Outbreaks 27 April 2011 24 May 2011

24. Hodographs Greensburg EF5 Parkersburg EF5

25. Outbreak Sounding

26. Energy Helicity Index (EHI) • Combination of CAPE and SRH • Two types: 0–1 km, 0–3 km • Thresholds • >2.5 : Favorable for tornadoes • Storms must develop for this to be useful • Can be skewed by high CAPE values

27. 0–1 km EHI: Outbreaks 27 April 2011 24 May 2011

28. Other Parameters • LCL Heights • Lower heights (<1000 m) associated with tornadoes • Higher moisture available, keeping RFD warm • Lifted Index (LI) • Another stability index (taken at 500 mb) • The lower the number, the more unstable the atmosphere

29. Other Parameters • Supercell Composite • Significant Tornado Parameter • For these two, we shall play a game!

30. But first… MATH! Not scary Chen math, but still a nuisance.

31. Game time!

32. Game time!

33. Where was the severe weather? ?

34. The point of STP & SCP • These are best used to pinpoint a region that severe weather could occur on a given day. • Should never be used to make any other decisions without actually analyzing the environment.

35. More things to look at! • Jet Stream • Increases shear • Separates downdraft from updraft • Longer-lived storms • Low-level Jet (LLJ) • Brings in moisture and warmer temperatures, increases shear and helicity • Upper-Level Jet Streaks • Increased shear, upward motion to increase instability • Upward regions: right entrance, left exit

36. 500 mb Jet: 27 April 2011

37. LLJ: 9 April 2011

38. Upper Level Jet Streak Left Exit RightExit Left Entrance Right Entrance

39. More things to look at! • Frontal boundaries • Cold and warm fronts, dryline • Can enhance shear, helicity • Source of lift • Surface observations • Gives an idea of what is going on at this moment • Look for mesoscale features • Satellite Imagery • Look for clearing early, robust CU fields

40. More things to look at! • Water Vapor Imagery • Shows drying, moistening in the mid- and upper-levels • See where fronts/shortwaves are located

41. More things to look at! • Moisture • Storms won’t form without it • Td > 60°F for best environment • 700 mb temperatures • Good indicator of cap strength • < 12°C in the spring without a strong lifting mechanism • Can be slightly higher (<13°C) during summer months or with strong lift

42. More things to look at! • Theta-E • Measure of heat and moisture in the atmosphere • Look for theta-e advection/ridges • Increased instability, convergence • Could be area of convective development • Storm Motion • Calculated average direction and speed of storms • Gives an idea of how storms will move

43. Where Do We Look At This Stuff? • SPC Mesoanalysis • TwisterData • COD Analysis • AMS Model Animator • HPC • RAP Weather

44. How to chase safely and effectively. Storm Chasing Basics.

45. The Beginner’s Way • S/SE is safest place to be • Watch for right-turning • Avoid core-punching • Avoid rain-wrapped messes • Pull off on side roads, not main roads

46. What NOT to expect… • To see a tornado on your first time out… • or second… • or third… • Good chasers usually see a tornado about once in every seven chases. • Don’t let this deter you from chasing… • Can’t win the game if you don’t play!

47. What to expect… • LONG car rides • Sitting, waiting, wishing… football and frisbee! • Lots of gas station/fast food meals • Sketchy dirt roads • And in turn, few rest stops. • The beauty of the Plains • Awesome tunes! • THE TIME OF YOUR LIFE! Memories!

48. Tips • Wear real shoes or boots, not flip flops. • Watch the skies, not just the computer screen. • Only your eyes can tell you what’s actually happening around you. • Try to learn as much as possible, not just watch.

49. So we’re not held liable if you act stupid. Just kidding. But seriously. Storm Chasing Safety.

50. Safety Tips • CHASE WITH SOMEONE WHO HAS CHASED BEFORE. • Chase with a partner • Stay in the car as much as possible if there’s lightning nearby. • Have an escape route • Try to head south if you feel that you’re in danger. • If that’s not possible, head east until you can go south.