ATM OCN 100 - Summer 2002 LECTURES 32 & 33

1. ATM OCN 100 - Summer 2002LECTURES 32 & 33 THUNDERSTORMS:MESOSCALE CONVECTIVE SYSTEMS A. INTRODUCTION • Practical Questions • What is a thunderstorm? • Why do thunderstorms occur? • Definitions (where...)

2. MADISON’S CURRENT WEATHER Madison Weather at 1000 AM CDT WED AUG 8 2001 Updated twice an hour at :05 and :25 Sky/Weather: SUNNY Temperature: 83 F (28 C) Dew Point: 71 F (21 C) Relative Humidity: 67% Wind: W7 MPH Barometer: 30.04F

3. Surface Weather Map from Today with Isobars & Fronts

4. Current Temperatures (oF) & Isotherms

5. Current Dewpoints (oF)

6. Current Winds Aloft at 34,000 Ft.

7. Tomorrow’s 7AM Forecast

8. A. INTRODUCTION (con’t.) • Definitions • A thunderstorm - contains thunder; • A thunderstorm day - a day with thunder. • A Mesoscale Phenomenon

9. Cumulonimbus

10. Thunderstorm Hazards-Lightning Lightning is a killer(with more than 80 deaths in US per year)!

12. Thunderstorm Hazards-Lightning Lightning is a killer(with more than 80 deaths in US per year)!

13. Historical Thunderstorm Charge Model

14. New Conceptual Model of Charge Structure in Deep Convection from Balloon Data

15. Thunderstorm Hazards-Flash Floods Flash Flooding is a killer(with more than 120 deaths in US per year)!

16. Thunderstorm Hazards-Tornadoes Tornadoes are killers(with more than 60 deaths in US per year)!

17. Funnel Cloud When funnel clouds touch the ground they become…….

18. Tornadoes

19. Thunderstorm Hazards-High Winds (Straight line)

20. Thunderstorm Hazards-Large Hail

21. B. THUNDERSTORM GENESIS • Essential Ingredients • Low Level Moisture • Unstable Atmospheric Lapse Rate • Trigger (or Kicker) • Initial Setting & Initiation Processes • Free Convection • Forced Convection

22. When Convection?

23. STABLE CONDITIONSCompare Environment with DALRColder parcel sinks & returns to start

24. ABSOLUTELY STABLE CONDITIONSCompare Environment with SALR & DALRColder parcel sinks & returns to start

25. UNSTABLE CONDITIONSCompare Environment with DALRWarmer parcel continues upward

26. ABSOLUTELY UNSTABLE CONDITIONSCompare Environment with SALR & DALRWarmer parcel continues upward

27. If STABLE CONDITIONS for DryCompare Environment with DALRColder parcel sinks & returns to start

28. But UNSTABLE CONDITIONS for HumidCompare Environment with SALRWarmer parcel continues upward

29. CONDITIONALLY STABLE CONDITIONSCompare Environment with SALR & DALR

30. Stability CriteriaSee Fig. 6.14 Moran & Morgan (1997)

31. STABILITY CRITERIA • Absolutely Stable • Layer lapse rate less than saturation adiabatic lapse rate. • Absolutely Unstable • Layer lapse rate greater than dry adiabatic lapse rate. • Conditionally Unstable • Layer lapse rate lies between dry & saturation adiabatic lapse rates.

32. STATIC STABILITY (con’t.) • Processes which change static stability (instability) • Cool below, but warm above (stabilize) • Warm below, but cool above (destabilize) • Visual stability indicators

33. Mammatus These pocket clouds form from sinking air ahead of the most severe thunderstorms. If you see these….run for cover!!!!

35. Hail Stones

36. Hail Storm

37. THE “TRIGGER” • Free Convection • Air ascends due to destabilization; • Heat surface and/or cool aloft. • Orographic Lifting • Air ascends mountain slopes. • Frontal Lifting • Air ascends along cold front. • Dynamic Lifting • Upper level motions induce lifting.

38. C. THUNDERSTORM TYPES • Single-Cell Thunderstorms • “Air Mass” Thunderstorms • Orographic Thunderstorms • Frontal Thunderstorms • Squall-Line Thunderstorms • Mesoscale Convective Complexes (MCC) • Multiple-Cell Thunderstorms

39. D. THUNDERSTORM CLIMATOLOGY • Geographical & Seasonal Distribution • Time of Day • Duration of Thunderstorms • Reported Thunderstorm Intensities

40. Thunderstorm ClimatologySee Fig. 13.9, Moran & Morgan (1997)

41. E. CHARACTERISTICS OF THUNDERSTORMS • The Thunderstorm Cell Model • Life Cycle of a Non-Severe Thunderstorm Cell • Where…

42. Cumulus Stage in thunderstorm life cycleSee Fig. 13.2a, Moran & Morgan (1997)

43. Mature Stage in thunderstorm life cycleSee Fig. 13.2b, Moran & Morgan (1997)

44. Dissipating Stage in thunderstorm life cycleSee Fig. 13.2c, Moran & Morgan (1997)

45. F. SEVERE THUNDERSTORMS • Official Criteria for Severe Weather • Large hail(3/4 inch or large diameter); • and/or • Damaging Winds(surface wind gusts of 58 mph or greater). • Unofficial Criteria for Severe Weather • Tornadoes, Heavy Precipitation, Flash Flooding, Deadly Lightning

46. Vertical Cross section of Severe ThunderstormSee Fig. 13.11, Moran & Morgan (1997)

47. Ingredients for severe thunderstorm episodeSee Fig. 13.13, Moran & Morgan (1997)

48. F. SEVERE THUNDERSTORMS (con’t.) • Types of Severe Thunderstorms • Structure of Severe Thunderstorms • Synoptic Situations Favoring Severe Thunderstorm Weather • Movement of Severe Thunderstorm Cells

49. NWS Watches & Warnings • Severe thunderstorm watch • Issued by National Weather Service to alert public that conditions are favorable for development of severe thunderstorms (large hail &/or high winds). • Severe thunderstorm warning • Issued by National Weather Service to warn public that a severe thunderstorm has been sighted by storm spotters or has been indicated by radar.

50. Hail ClimatologySee Fig. 13.24, Moran & Morgan (1997)