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

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

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 inches of snow in a matter of hours ► Although rare, can profoundly affect the daily life of the average person.

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

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

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

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

Overview Eau Claire Wisconsin 23 March 1966

Meteorogram for EAU 6 pm, 3/ am, 3/23

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”

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

L Surface Analysis 0000 UTC 23 March 1966

850 mb Heights and Temperatures

700 mb Heights and Temperatures

700 mb  e

500 mb Heights and Vorticity

Q-vector Divergence

mb Layer Mean Relative Humidity

300 mb Heights and Isotachs

Q-vector Divergence

Location of First Cross-Section

Cross-Section Analysis EAU

Vertical Profile of EPV3

Vertical Profile of Frontogenesis

Vertical Profile of  e

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

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

L Surface Analysis 1200 UTC 23 March 1966

850 mb Heights and Temperatures

700 mb Heights and Temperatures

700 mb  e

500 mb heights and Vorticity

Q-Vector Divergence

Layer Mean Relative Humidity

300 mb Heights and Isotachs

Location of Second Cross-Section

Cross-Section Analysis EAU

Vertical Profile of EPV3

Vertical Profile of Frontogenesis

Vertical Profile of Theta E

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

Meteorogram for EAU 6 pm, 3/ am, 3/23

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”

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 mb layer ► EPV and CSI present in a cross-section analysis

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 mb layer of Q-vectors ► Completes the composite work done by Oravetz (2003)

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

Acknowledgments ► National Science Foundation ► National Climatic Data Center