1. HOLLY, COLORADO TORNADO 28 MARCH 2007 Bill Eckrich DayWeather, Inc. Cheyenne, Wyoming

2. Overview of Holly, Colorado  Located in southeastern Colorado on U.S. Highway 50 in far eastern Prowers County, 28 miles east of Lamar and approximately 5 miles from the Kansas state line  Population 1,048 (2000 U.S. Census)

3. Holly Tornado Statistics  First touched down at 1957 MDT one mile south of Holly  WFO PUB Tornado Warning issued at 2000 MDT  Rated as high-end EF3  Moved just east of north across the entire town causing EF1 to low-end EF3 damage  2 fatalities, one within a day and another nearly a month later, with 10 injuries  Path length 28 miles over a 25-30 minute period  Damage width in Holly was 1000 feet wide

4. Holly Tornado Statistics  48 structures destroyed  100+ structures damaged  Event occurred outside of both the SPC slight and moderate risk areas (12Z, 13Z, 1630Z, 20Z, 01Z) as well as the later-issued Tornado Watch #83  Colorado convection evolved from a retreating dryline possibly caused by stronger-than-forecast ageostrophic forcing from northward-propagating shortwave

5. SPC DAY1 OUTLOOK (20Z)

6. TORNADO WATCH #83 HOLLY

7. SYNOPTIC AND MESOSCALE ENVIRONMENT INCLUDING RADAR AND SATELLITE DATA

8. 00Z 29 March 300mb NOSE OF JET STREAK

9. 00Z 29 March 500mb

10. 00Z 29 March 700mb

11. 00Z 29 March 850mb THERMAL RIDGE

16. 2116Z 28 March

17. 2316Z 28 March

18. 0200Z 29 March

19. IR SATELLITE 0100Z 29 MARCH

20. VISIBLE SATELLITE 0130Z 29 MARCH

21. 0153Z 29 MARCH

22. 0157Z 29 MARCH

24. 0202Z 29 MARCH

26. HOLLY Prowers County Kiowa County Kansas

28. EF3 Damage in Holly WFO Pueblo

29. EF3 Damage in Holly WFO Pueblo

30. High-end EF3 Damage 12N of Holly WFO Pueblo

31. High-end EF3 Damage 12N of Holly WFO Pueblo

32. Courtesy Ty Harmon - KLMR

36. CONCLUSIONS  Large and deep storm system over the central Rockies  Large-scale ascent across eastern Colorado, southwestern Nebraska, western Kansas and the Oklahoma/Texas panhandles  Surface winds ahead of the dryline backed with time as the shortwave/jet streak approached  Dryline retreated  SRH increased with backing winds relative to storm motion

37. CONCLUSIONS  First tornado deaths in Colorado since June 27, 1960  Only the second killer tornado in Colorado since 1950  Earliest strong tornado in Colorado history Previous: 3/29/1910 in Sedgwick County  Earliest killer tornado in Colorado history Previous: 4/30/1942 in Bent/Kiowa counties

38. CONCLUSIONS  Prowers County has had only one prior significant tornado  June 24, 1968  One injury  Occurred within one mile of Holly