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

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)

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 minute period  Damage width in Holly was 1000 feet wide

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

SPC DAY1 OUTLOOK (20Z)

TORNADO WATCH #83 HOLLY

SYNOPTIC AND MESOSCALE ENVIRONMENT INCLUDING RADAR AND SATELLITE DATA

00Z 29 March 300mb NOSE OF JET STREAK

00Z 29 March 500mb

00Z 29 March 700mb

00Z 29 March 850mb THERMAL RIDGE

2116Z 28 March

2316Z 28 March

0200Z 29 March

IR SATELLITE 0100Z 29 MARCH

VISIBLE SATELLITE 0130Z 29 MARCH

0153Z 29 MARCH

0157Z 29 MARCH

0202Z 29 MARCH

HOLLY Prowers County Kiowa County Kansas

EF3 Damage in Holly WFO Pueblo

EF3 Damage in Holly WFO Pueblo

High-end EF3 Damage 12N of Holly WFO Pueblo

High-end EF3 Damage 12N of Holly WFO Pueblo

Courtesy Ty Harmon - KLMR

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

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

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