The 1965 Palm Sunday tornado outbreak was a historic severe weather event that affected the Midwestern and Southeastern United States on April 10–12, 1965.

[13] 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.

[14][15] 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.

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.

[15][16] 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).

[16][17] 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).

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.

[15][14][19] 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.

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.

The tornado, now 500 to 800 yards (460 to 730 m) wide, then restrengthened and felled mature oak trees as it crested a precipitous hill before striking Bay View Beach.

In Island Lake the tornado tossed boats ashore, wrecked piers, and caused homes to collapse, resulting in one additional death.

As Huffman and his wife Betty awaited the storm, he noticed the tornado approaching from the southwest, so he began taking a series of photographs, six in all.

(Roughly 45 minutes later, another F4 tornado passed just to the north of the Midway Trailer Court, splitting into yet another pair of funnels as it struck the Sunnyside neighborhood in Dunlap.)

The tornado obliterated roughly 80% of the trailer park, with 10 deaths, and caused F4 damage to numerous other homes near Middlebury, some of which were swept clean.

[31] With the telephone lines down, emergency services in Elkhart County, Indiana, could not warn Michigan residents that the tornadoes were headed their way.

Weather Bureau Office (WBO) observed that the thunderstorms over Northern Indiana and western Lower Michigan were moving east-northeastward at 70 mph (110 km/h).

Starting just south of the Indiana-Michigan state line, near Orland, the first, deadliest, and strongest of two massive tornadoes, each rated F4, debarked trees and leveled homes on the shoreline of Lake Pleasant in Steuben County.

After striking Coldwater Lake, the tornado widened even further, up to 2 miles (3.2 km) across, destroying a century-old farmhouse and killing a family of six near Reading.

The Wolverine Plastics building on the Monroe County side of town, then the top employer in the village, was destroyed with the roof being completely removed in the process.

The Palm Sunday Tornado Memorial Park now exists near this location, at the corner of County Road 45 and Cole Street in Dunlap (41°38′29″N 85°55′31″W / 41.641522°N 85.925157°W / 41.641522; -85.925157).

The tornado then widened to 1 mile (1.6 km) across as it moved into nearby Alto, causing F4-level damage to homes, before striking the southern edge of the larger city of Kokomo.

As it struck the southern outskirts of Marion, the tornado leveled a pair of homes, partly unroofed a Department of Veterans Affairs (VA) hospital, and wrecked the Panorama shopping center.

Across Northern Illinois, numerous funnel clouds were sighted in Wheaton, Carol Stream, Winfield, West Chicago, Aurora, and Rockford, respectively.

[37][15][21][38] It occurred on Palm Sunday, an important day in the Christian religion, and many people were attending services at church, one possible reason why some warnings were not received.

For many areas, April 11 marked the first day of above-average temperatures, so members of the public, being outdoors or attending services, failed to receive updates from radio and television.

Officials of the severe storms forecast center in Kansas City met with WMT meteorologist Conrad Johnson and News Director Grant Price.

Additionally, communities began activating civil defense sirens during tornado warnings, and storm spotting via amateur radio networks and other media received increased logistical support and emphasis, leading to the eventual creation of SKYWARN.

A strong jet stream, combined with tornadoes, lofted topsoil from Illinois and Missouri eastward, producing hazy skies prior to the arrival of storms.