Lably
Skip to content

1965 Palm Sunday tornado outbreak

Natural disaster in the US

  • 19 min read
  • 5 chapters
1965 Elkhart, Indiana double tornado on Palm Sunday . This is one of the most incredible tornado photographs ever taken, between Goshen and Elkhart on Palm Sunday, the "double tornado" destroying the
Paul Huffman (d. 2014) [1] · Public domain

Related on Lably

Through Tornado, Jet stream and Troposphere

In 2023, tornado expert Thomas P. Grazulis created the outbreak intensity score (OIS) as a way to rank various tornado outbreaks. The 1965 Palm Sunday tornado outbreak received an OIS of 238, making it the fourth-worst tornado outbreak in recorded history.

Meteorological synopsis

A vigorous extratropical cyclone centered over the northeastern High Plains, in the region of the Dakotas, was the primary catalyst for widespread severe weather on April 11, 1965. As early as the preceding day, a strong jet stream in the upper two-thirds of the troposphere traversed the southern Great Plains and was responsible for an outbreak of tornadoes from the Kansas–Missouri border to Central Arkansas, including a violent F4 tornado that struck the town of Conway in Faulkner County, Arkansas, killing six people and injuring 200. The following morning, at 7:00 a.m. CDT (12:00 UTC), data from radiosondes indicated wind speeds of 120–150 kn (140–170 mph; 220–280 km/h) between the altitudes of 18,000–30,000 ft (5,500–9,100 m) over the Sonoran–Chihuahua Deserts and the Arizona/New Mexico Mountains. Meanwhile, at 10,000 ft (3,000 m), winds of 70 kn (81 mph; 130 km/h) impinged on the southern Great Plains. Retreating northward, a warm front interacted with a shortwave to produce isolated thunderstorms from northern Missouri and Central Illinois to the Lower Peninsula of Michigan.

The well-defined surface cyclone over the High Plains intensified as it headed into Iowa, its central pressure decreasing from 990 to 985 mb (29.23 to 29.09 inHg) by 1:00 p.m. CDT (18:00 UTC). As the warm front bisected central Iowa and stretched into Illinois and Indiana, a cold front and very dry air aloft—indicative of a potent elevated mixed layer—departed from eastern Kansas. Strong winds transported steep lapse rates within the elevated mixed layer eastward across the Great Plains. Concomitant destabilization of the atmosphere occurred over the warm sector due to abundant sunshine from the elevated mixed layer. High temperatures ranged from 83 to 85 °F (28 to 29 °C) from Chicago to St. Louis. Simultaneously, a strong low-level jet stream brought a moistening air mass northward: dew points of at least 60 °F (16 °C) reached southernmost Illinois and Indiana by 10:00 a.m. CDT (15:00 UTC). Meanwhile, a pronounced dry line-like boundary near the cold front moved into eastern sections of Arkansas and Missouri. Weather stations from Topeka, Kansas, to Peoria, Illinois, showed very strong vertical shear that favored intense low-level convergence—combined with a moist dew point in the warm sector, an environment favorable for supercell thunderstorms.

A weather balloon launched from Dodge City, Kansas recorded winds of 185 mph (298 km/h) aloft; another at Peoria, Illinois, subsequently measured 135 kn (155 mph; 250 km/h). Minimum dew points of 60 °F (16 °C) reached as far north as southern Michigan by mid afternoon. Volatile atmospheric conditions led to thunderstorm activity over eastern Iowa by 1:40–48 p.m. CDT (18:40–48 UTC), the first supercell of which produced the initial tornado of the day. By 6:00 p.m. CDT (23:00 UTC), instability reached record proportions for the time of year over a wide area, with convective available potential energy (CAPE) of at least 1,000 J/kg in the mixed layer over much of Indiana and southernmost Michigan. Record-breaking ambient vertical wind shear in the lowest 6 km (3.7 mi; 20,000 ft; 6,000 m) of the atmosphere facilitated the explosive development of long-lived mesocyclones and thus long-tracked tornado families. The very strong shear and rapid forward speed of the storms—up to 70 mph (110 km/h) in some cases—may have enhanced the formation of cyclic supercells and could account for numerous reports of multiple mesocyclones and twin tornadoes, including the famous "twin tornadoes" near Elkhart, Indiana; similar conditions yielded the Tri-State Tornado, the longest-tracked and deadliest in U.S. history, on March 18, 1925.

At 11:45 a.m. CDT (16:45 UTC) on April 11, the Severe Local Storms Unit (SELS) in Kansas City, Missouri, issued an outlook that mentioned the possibility of tornadoes from northeastern Missouri to the northernmost two-thirds of Indiana. At 2:00 p.m. CDT (19:00 UTC)—fifteen minutes after the first tornado was spotted—the first tornado watch of the day was issued, covering portions of northern Illinois and southern Wisconsin. A total of four watches were issued on April 11–12. Radio news reporter Martin Jensen, then stationed at the WMT Station in Cedar Rapids, reported the first tornado of the day forming at 1:45 p.m. CDT (18:45 UTC). The station was equipped with a Collins Radio aviation radar mounted on the roof of the station building and was used to support severe weather reports on local and regional newscasts. After detecting the severe thunderstorm, the reporter called Weather Bureau offices in Waterloo (which had no radar) and Des Moines to alert them about the storm. The phone call became the first hard evidence for the Weather Bureau regarding the growing threat of severe storms that spawned dozens of tornadoes over the next 12 hours. For the first time in the U.S. Weather Bureau's history, an entire Weather Bureau Office's jurisdiction, in Northern Indiana, was under a tornado warning; this was termed a "blanket tornado warning" and was later used by several National Weather Service (NWS) offices on April 3, 1974.

Sign in to keep reading

4 more chapters are free with a Lably account.

More in Earth science