1. Characteristics of an Anomalous, Long-Lived Convective Snowstorm Rebecca L. Ebert Department of Soil, Environmental, and Atmospheric Sciences University of Missouri-Columbia SEAS 410: Seminar 29 March 2004

2. Outline ► Introduction  What is Thundersnow?  Where does it happen? ► Motivation ► Data Used ► Synoptic Analysis ► Case Study ► Results ► Conclusion and Future Work

3. Introduction ► Thundersnow- A convective thunderstorm like those you see in the spring and summer, except this occurs in the winter.  Can produce: ► Blizzard-like conditions almost instantaneously ► Heavy banded precipitation structures that can produce 12-24 inches of snow in a matter of hours ► Although rare, can profoundly affect the daily life of the average person.

4. Introduction Cont. ► For 20 years researchers have studied the atmospheric link between routine snowstorms and those with convection. ► They assume that the ingredients are dynamic in nature  Occur around a surface cyclone  Or lake area in association with surface-based instability

5. Motivation ► The purpose of this study is to reveal the dynamic characteristics of a particularly strong, long-lived convective snowstorm. ► The case that is studied was very unique with 9 non-consecutive hours of thundersnow reported  The longest lasting event on record of which we are aware  Observers witnessed lightning numerous times during the event

6. Motivation cont. ► With this work we expect to support the efforts of previous investigators  Investigations by Market et al.(2002) revealed: ► Two maxima of thundersnow occurrences  Rocky Mountains  Central Plains ► Location of thundersnow events in the Central Plains:  Often occurs northwest or northeast of a surface cyclone  Oravetz (2003) performed a composite study of thundersnow occurrences northwest and northeast of surface cyclones

7. Data Used ► Surface Observations  Temperature  Relative humidity  Wind direction  Visibility  Current weather conditions ► Rawinsonde observations  Upper air analysis  Sounding profiles ► Objective Analysis  Atmospheric characteristics observed during analysis

8. Overview Eau Claire Wisconsin 23 March 1966

9. Meteorogram for EAU 6 pm, 3/22 - 9 am, 3/23

10. Storm Total Snowfall (inches) 48 hr accumulations ending 6 pm, 3/23/1966 1” 5” 10” 1” 10” 5” 15” 10” 5” 5”5” 15” 10” 15” 5” 1” 5” 1” 5” 10” 15” 1”

11. Synopsis 0000 UTC 23 March 1966 (6 pm CST 22 March 1966)

12. L Surface Analysis 0000 UTC 23 March 1966

13. 850 mb Heights and Temperatures

14. 700 mb Heights and Temperatures

15. 700 mb  e

16. 500 mb Heights and Vorticity

17. Q-vector Divergence

18. 850-500 mb Layer Mean Relative Humidity

19. 300 mb Heights and Isotachs

20. Q-vector Divergence

21. Location of First Cross-Section

22. Cross-Section Analysis EAU

23. Vertical Profile of EPV3

24. Vertical Profile of Frontogenesis

25. Vertical Profile of  e

26. Summary (0000 UTC) ► Eau Claire, Wisconsin is located northeast of a surface cyclone  Warm air advection (WAA) is present at 850 mb and 700 mb  A semblance of a TROugh of Warm air ALoft (TROWAL) is visible on the 700 mb  e map  A positively tilted trough at 500 mb  Q Convergence downstream of event location  Plenty of available moisture  Left exit region of a 70 knot curved jet streak  Presence of Equivalent Potential Vorticity (EPV) and Conditional Symmetric Instability (CSI) present in Eau Claire.  Producing slantwise convection

27. Synopsis 1200 UTC 23 March 1966 (6 am CST 23 March 1966) (6 am CST 23 March 1966)

28. L Surface Analysis 1200 UTC 23 March 1966

29. 850 mb Heights and Temperatures

30. 700 mb Heights and Temperatures

31. 700 mb  e

32. 500 mb heights and Vorticity

33. Q-Vector Divergence

34. 850-500 Layer Mean Relative Humidity

35. 300 mb Heights and Isotachs

36. Location of Second Cross-Section

37. Cross-Section Analysis EAU

38. Vertical Profile of EPV3

39. Vertical Profile of Frontogenesis

40. Vertical Profile of Theta E

41. Summary (1200 UTC) ► Eau Claire, Wisconsin is located northwest of a surface cyclone  Warm air advection (WAA) is present at 850 mb east of the location  The TROWAL is visible on the 700 mb  e map almost directly over Eau Claire, WI  A negatively tilted trough at 500 mb is now present  Q convergence downstream of event location has weakened but is still relative strong  Deep moisture is still present  Jet streak has increased to 90 knots, with Eau Claire still in the left exit region  Presence of Equivalent Potential Vorticity (EPV) and Conditional Symmetric Instability (CSI) present in Eau Claire.  Producing slantwise convection

42. Meteorogram for EAU 6 pm, 3/22 - 9 am, 3/23

43. Storm Total Snowfall (inches) 48 hr accumulations ending 6 pm, 3/23/1966 1” 5” 10” 1” 10” 5” 15” 10” 5” 5”5” 15” 10” 15” 5” 1” 5” 1” 5” 10” 15” 1”

44. Conclusions ► A long-lived thundersnow event occurred at Eau Claire, WI for 9 non-consecutive hours ► In the beginning of this event Eau Claire was northeast of a surface cyclone at 0000 UTC  Present features included: ► Ample moisture ►  e pattern reveals a slight ridge southeast of the event sites and east of the 700 mb low ► Forcing for ascent  Strong convergence in the 400-700 mb layer ► EPV and CSI present in a cross-section analysis

45. Conclusions Cont. ► As the system progressed over a 12 hour period, Eau Claire became northwest of the surface cyclone at 1200 UTC  Present features included: ► Ample moisture ►  e pattern at 700 mb indicates a TROWAL right over the Eau Claire location ► Forcing for ascent  Again convergence is present in the 400-700mb layer of Q-vectors ► Completes the composite work done by Oravetz (2003)

46. Future Work ► Incorporate the Workstation Eta (WSEta) model run analysis of this event  Compare the model run with the actual observations from the event, correlating if the model can forecast such events  Calculate slantwise convective available potential energy (SCAPE) during the event

47. Acknowledgments ► National Science Foundation ► National Climatic Data Center