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Case Studies of Midwestern Thundersnow Events

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Case Studies of Midwestern Thundersnow Events CASE STUDIES OF MIDWESTERN THUNDERSNOW EVENTS ————————————————– A Thesis Presented to the Faculty of the Graduate School University of Missouri-Columbia ————————————————– In Partial Fulfillment for the Degree Master of Science ————————————————– by CHRISTOPHER E. HALCOMB Dr. Patrick S. Market, Thesis Supervisor DECEMBER 2001 COMMITTEE IN CHARGE OF CANDIDACY: Assistant Professor Patrick S. Market Chairperson and Advisor Professor William B. Kurtz Assistant Professor Anthony R. Lupo i Acknowledgements I will begin by thanking my advisor, Dr. Patrick Market, for allowing me the opportunity to study this fascinating subject and allowing me to largely run with it as I saw fit, but giving guidance when I truly needed it. I would like to thank him most for being a great friend and filling my life with humor and laughter. I would also like to thank Dr. Anthony Lupo, who was always willing to help anytime that I asked for it. I also consider him a great friend and I will always treasure the times the three of us have had together. I would like to thank Rebecca Ebert for assisting in the generation of many of the figures that are included in the thundersnow climatology, and for not killing me when I asked her to do just one more thing for me. I would like to acknowledge Jorge Flores for his expertise in writing the computer program to search for all possible combinations in which snow and thunder can occur simultaneously. It would have taken me forever to write such a program. I am deeply appreciative of the support that I have received from my mother and my grandmother, who are two of the kindest and most sincere persons that I have known. They have both been supportive of whatever endeavor that I chose to pursue and through thick and thin. I would also like to thank Cyri Parks for being such a good and supportive friend the last few months. I really am glad that I was able to get to know her. We are so much alike in so many ways. She will always fill a special place in my heart. ii Contents 1 Introduction 1 1.1 Statement of Thesis . ....................... 4 2 Literature Review 5 2.1 Studies on Banded Precipitation . ................ 5 2.2 Thundersnow-related Climatology . ................ 20 2.3 Summary . .............................. 22 3 Methodology 24 3.1 Climatology . .............................. 24 3.2 Case Studies . .............................. 26 3.2.1 9 December 1999, 11 March 2000, and 19 April 2000 . ..... 27 3.2.2 5 December 1999 . ....................... 30 4 Thundersnow Climatology 31 4.1 Spatial and Temporal Patterns ....................... 31 4.2 Characteristics of Thundersnow Observations . ............ 35 5 Case Studies 40 5.1 5 December 1999 .............................. 40 5.1.1 Introduction . ....................... 40 5.1.2 Surface Analysis . ....................... 40 5.1.3 Upper Air Analysis . ....................... 41 5.1.4 Isentropic Analysis . ....................... 42 5.1.5 Stability Analysis . ....................... 46 5.1.6 Quasigeostrophic Forcing . ................ 46 5.1.7 Conclusions . ....................... 47 5.2 9 December 1999 .............................. 49 5.2.1 Introduction . ....................... 49 iii 5.2.2 Surface Analysis . ....................... 49 5.2.3 Upper Air Analysis . ....................... 50 5.2.4 Isentropic Analysis . ....................... 51 5.2.5 Stability and Forcing . ....................... 54 5.2.6 Conclusions . ....................... 59 5.3 11 March 2000 . .............................. 60 5.3.1 Introduction . ....................... 60 5.3.2 Surface Analysis . ....................... 60 5.3.3 Upper Air Analysis . ....................... 60 5.3.4 Isentropic Analysis . ....................... 61 5.3.5 Stability and Forcing . ....................... 64 5.3.6 Conclusions . ....................... 68 5.4 19 April 2000 . .............................. 70 5.4.1 Introduction . ....................... 70 5.4.2 Surface Analysis . ....................... 70 5.4.3 Upper Air Analysis . ....................... 70 5.4.4 Isentropic Analysis . ....................... 75 5.4.5 Stability and Forcing . ....................... 75 5.4.6 Conclusions . ....................... 78 6 Discussion and Conclusions 81 6.1 Discussion of Case Studies . ....................... 81 6.2 Conclusions . .............................. 82 References 85 Vita 88 iv List of Figures 1 g 2.1 Relationship of e (dashed, K) and M (solid, m s ) in the eval- uation of CSI, CI, and WSS (Reproduced from a figure originally constructed by Dr. James T. Moore and Sean Nolan at Saint Louis University). .................................. 10 2.2 Lifted indices for various air parcels for North Omaha, Nebraska (OVN) at 0000 UTC on 21 February 1993 (Reproduced from Moore et al. 1998). ................................. 11 2.3 T-log P plot of e (K) at North Omaha, Nebraska (OVN) at 0000 UTC on 21 February 1993. (Reproduced from Moore et al. 1998). ..... 12 2.4 Conceptual model depicting the frontogenetical region and zone of EPV reduction in a developing cyclone (Reproduced from Nicosia and Grumm 1999). ............................. 13 2.5 Proposed positive feedback mechanism between frontogenesis and the reduction of EPV (Reproduced from Nicosia and Grumm 1999). .14 2.6 Observed 24-hour snowfall totals (cm) ending at 0000 UTC on 20 January 1995. (Reproduced from Martin 1998b). ............ 15 2.7 Cloud-to-ground lightning strikes in a 24-hour period ending at 0000 UTC 20 January 1995 (Reproduced from Martin 1998b). ....... 15 v 2.8 (a) 6-hour forecast of 200-m frontogenesis from the UW-NMS model valid at 0600 UTC 19 January 1995. Shaded regions denote positive 1 1 frontogenesis every 1 K (100 km) day . (b) As in (a) except from a 12-hour forecast valid at 1200 UTC on the same day. (c) As in (a) except from a 18-hour forecast valid at 1800 UTC. (d) As in (a) except from a 24-hour forecast valid at 0000 UTC 20 January 1995. (e) As in (a) except from a 30-hour forecast valid at 0600 UTC 20 January 1995. (Reproduced from Martin 1998a). ............ 16 ~ 2.9 Schematic showing the natural coordinate partioning of Q . Dashed lines depict isentropes on an isobaric surface (Reproduced from Martin 1999). ................................. 17 ~ Q 2.10 The effect of s on horizontal thermal structure. (a) Isentropes ~ (solid lines) in a field of Q, with the maximum region of convergence shaded. Dashed line indicates convergence axis, while r depicts thermal gradient. (b) Thick black arrow depicts original direction of r r , while thick gray arrow depicts the direction of after being ro- ~ Q tated by s . (c) Oriention of thermal zone in (a) after being rotated ~ Q by s (Reproduced from Martin 1999). .................. 18 16 ~ Q 5 10 2.11 (a) Convergence of s contoured and shaded every m 1 1 kg s in the 600-900 hPa layer from an 18-hour forecast of the UW-NMS model valid at 0600 UTC 23 October 1996. (b) As in (a) ~ Q except for n (Reproduced from Martin 1999). ............. 19 2.12 Defintions of several types of instabilities (Reproduced from Schultz and Schumacher 1999). .......................... 19 2.13 Mean proximity sounding for 13 thundersnow reports during the pe- riod of 1968-1971. The thick, solid line depicts the temperature pro- file. The thick, dashed line depicts the dewpoint profile (Reproduced from Curran and Pearson 1971). ..................... 21 2.14 Number of hours of thunder at temperatures below 0 C from 1982- 1990. (Reproduced from Holle et al. 1998). ............... 22 3.1 Delineation of regions used in the thundersnow climatology. ..... 25 vi 4.1 Number of thundersnow events for each region during the period of 1961-1990. Refer to regions depicted in Fig. 3.1. ............ 32 4.2 Number of thundersnow events for each state during the period of 1961-1990. Note that the sum of the events will not equal 375 (Refer to Section 3.1). ............................... 33 4.3 As in Fig. 4.1 except events (N=375) by category (Refer to Section 3.1 for the description of categories). ................... 34 4.4 As in Fig. 4.2 except with normalized values. .............. 35 4.5 As in Fig. 4.1 except by month (N=375). ................. 36 4.6 As in Fig. 4.1 except by Local Standard Time (LST) (N=375). ..... 36 4.7 Polar plot showing the location of thundersnow events (Category 1) relative to the position of the center of the parent low (N=247). Direction is given in the traditional meteorological azimuth (degrees) from the postion of the low to the observing station. Distances are given in km. ................................. 37 4.8 As in Fig. 4.1 except by distance (km) from parent low center of initial report (N=375). ............................ 38 4.9 Representative station model for the average initial report for all thundersnow events (N=375). Temperature and dewpoint are given in degrees F, the wind speed in knots, and the sea level pressure in hPa. The standard deviation for all parameters is also represented. .38 4.10 As in Fig. 4.1 except by snowfall intensity of initial report (N=375). .. 39 5.1 Surface analysis valid at 0600 UTC on 5 December 1999. Isobars drawn every 2 hPa. Red line depicts cross section line. ........ 41 5.2 Radar mosaic valid at 0600 UTC on 5 December 1999 (obtained from the National Climatic Data Center). ................. 42 5.3 850-hPa Rapid Update Cycle initial field analysis valid at 0600 UTC on 5 December 1999. Isotherms (thick lines) drawn every 4 C, height contours (thin lines) every 2 dkm. ................. 43 vii 5.4 As in Fig. 5.3 except for 300-hPa level. Height contours (thick lines) drawn every 5 dkm, isotachs (thin lines) every 10 knots (2=20 kts, 12=120 kts, etc. ............................... 43 5.5 As in Fig. 5.3 except for 300-hPa divergence (depicted every 2 5 1 10 s ). ................................... 44 5.6 As in Fig. 5.3 except for 700-hPa equivalent potential temperature (depicted every 2 K). ............................ 45 5.7 As in Fig. 5.3 except dynamic tropopause pressures (depicted every 50 hPa). ................................... 45 5.8 Vertical cross section analysis of the 0600 UTC Rapid Update Cycle initial field from 5 December 1999.
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