Draft:1974 DePauw tornado

Depauw-Daisy Hill, Indiana

Meteorological history
Formed	April 3, 3:20 p.m. CDT (UTC-5:00)
Dissipated	April 3, 4:29 p.m. CDT (UTC-5:00)
Duration	69 minutes
F5 tornado
on the Fujita scale
Overall effects
Casualties	6 fatalities, 86 injuries

Meteorological synopsis

By 12:00 UTC on April 3, a large-scale trough extended over most of the contiguous United States, with several modest shortwaves rotating around the broad base of the trough. The mid-latitude low-pressure center over Kansas continued to deepen to 980 mb (28.94 inHg), and wind speeds at the 850-mb level increased to 50 kn (58 mph) (25.7 m/s (93 km/h)) over portions of Louisiana, Mississippi, and Alabama. Due to significant moisture advection, destabilization rapidly proceeded apace; the warm front near the Gulf Coast dissipated and then redeveloped northward over the Ohio River valley. Consequently, CAPE levels in the region rose to 1,000 J/kg. However, a warm temperature plume in the elevated mixed layer kept thunderstorms from initiating at the surface. Meanwhile, a large mesoscale convective system (MCS) that had developed overnight in Arkansas continued to strengthen due to strong environmental lapse rates. Later in the day, strong daytime heating caused instability to further rise. By 18:00 UTC, CAPE values in excess of 2,500 J/kg were present over the lower Ohio and the Mississippi Valley. As wind speeds in the troposphere increased, Large-scale lifting overspread the warm sector. At the same time, the forward-propagating MCS spread into the Tennessee and Ohio valleys, where it evolved into the first of three main convection bands that produced tornadoes. This first convective band moved rapidly northeast, at times reaching speeds of about 60 kn (69 mph) (30.9 m/s (111 km/h)). However, thunderstorm activity, for the moment, remained mostly elevated in nature.

By 16:30 UTC, the large MCS began to splinter into two sections: the southern part slowed, lagging into southeast Tennessee, while the northern part accelerated, reaching Pennsylvania by 19:30 UTC. The split was related to several factors, including a band of subsidence over eastern Kentucky and western West Virginia; local downslope winds over the Appalachians; and an inversion over the same area. These factors allowed the northern part of the MCS to accelerate due to efficient ducting, while the southern part slowed as the boundary layer warmed and moistened. Numerous surface-based supercells began to develop in the southern area, beginning with one that produced an F3 tornado at about 16:30 UTC near Cleveland, Tennessee. Meanwhile, a new band of scattered thunderstorms developed at 15:00 UTC over eastern Arkansas and Missouri; over the next four hours, this band became the focus for several intense supercells, starting in eastern Illinois and southern Indiana. In the wake of the MCS, backing low-level winds, rapid diurnal destabilization, and perhaps cool, mid-level advection had occurred over the warm sector, weakening the convective inhibition (CINH) layer, and favorable wind profiles bolstered helicity to over 230 m²/s²—a combination of factors conducive to tornadogenesis. Consequently, the storms increased in intensity and coverage as they moved into Illinois, Indiana, and northern Kentucky, producing several tornadoes, including the DuPauw tornado.

Tornado summary

Of the F5 tornadoes produced by the outbreak, the Depauw-Daisy Hill tornado was the first to form, touching down at 3:20 pm local time. It is probably the least-known of the F5 tornadoes in the outbreak as it traveled through rural areas in southern Indiana northwest of Louisville, traversing about 65 miles (105 km) through parts of Perry and Harrison Counties. F5 damage was observed near the community of Depauw, where numerous farms were leveled. Areas near Palmyra and Borden were also heavily affected by the tornado. Morgan Elementary School in northern Harrison County Indiana was directly hit by the tornado. Four classrooms were destroyed and the roof was removed from the school and placed on the cars of the faculty. Fortunately, the children and faculty, who were huddled in the hallways, were not injured. All but 10 homes in Martinsburg were destroyed; and in the Daisy Hill community homes were completely swept away at F5 intensity. Published photographs of this storm reveal a very wide debris cloud and wall cloud structure, with no visible condensation funnel at times. Overall, six were killed by the storm and 86 were injured. One of the fatalities occurred when a woman was crushed by a school bus that flew into a ditch she was sheltering in. The tornado had a peak width of 700–1,760 yards (640–1,610 m).

Notes and references