Tornado outbreak of November 30 – December 2, 2018

The first advertised threat for organized severe weather came on November 26, when the Storm Prediction Center (SPC) outlined a day 5 risk area across portions of the Southern Plains.[2] A large slight risk was introduced for portions of Oklahoma, Texas, Arkansas, Louisiana, and Mississippi on November 28,[3] with an upgrade to enhanced risk for much of those same locations the next morning.[4] On November 30, a vigorous shortwave trough—part of an active wave train within the subtropical jet—progressed from Arizona into the Central Plains. The Storm Prediction Center maintained an enhanced risk for severe weather, including a 10% hatched risk area for tornadoes. As an expansive 110–140 kn (130–160 mph; 200–260 km/h) jet stream pushed through the trough, it began to take on a negative tilt. A surface low developed over Colorado in response, pushing into eastern Kansas by early on December 1. Despite a confined warm sector, the combined influence of moderate CAPE around 500–1,500 J/kg, an 850 mb (hPa) jet stronger than 50 kn (58 mph; 93 km/h), low lifted condensation levels (LCLs), cold temperatures aloft (steep lapse rates), weakening convective inhibition (CIN), and persistent moisture transport (warm-air advection (WAA)) resulted in the formation of semi-discrete supercells and quasi-linear convective systems (QLCSs) that resulted in widespread damaging wind reports and several tornadoes.[5][6] In Oklahoma, a large and long-tracked EF2 wedge tornado impacted areas near Tenkiller Ferry Lake, damaging or destroying many homes and other structures, downing countless trees, and injuring 5 people. Another EF2 tornado struck Van Buren, Arkansas, causing major damage to several homes. A few other weak tornadoes were also confirmed.[7]

The EF3 wedge tornado that caused major damage in Taylorville, Illinois and injured 22 people.

During the very early morning hours of December 1, an EF1 tornado struck the southern part of Aurora, Missouri, killing one person at a motel and damaging a few other nearby businesses. Later that day, the deepening area of low pressure—initially over Kansas—shifted into Iowa as it occluded. The aforementioned shortwave progressed into the Mississippi River Valley, supporting the formation of a secondary surface low pressure over Missouri that moved toward the Great Lakes. A mid-level area of low pressure was centered farther west near the surface low, and was a cold-core low, within a longwave trough extending over the outbreak area and which provided cold air aloft, steeper lapse rates, and thus higher convective instability. Low level instability as measured by surface to 3 km (10,000 ft) CAPE was also significant, especially for a cold-core setup, reaching values of 200 J/kg. Within the warm sector of this feature, a pronounced dry slot allowed for relatively substantial destabilization, with mixed-layer CAPE increasing to 500–1,200 J/kg. Strong deep-layer shear and pronounced low-level directional shear as a result of backed surface winds contributed to enlarged bell-shaped hodographs, with dew points upwards of 60 °F (16 °C), resulting in an outbreak of tornadic supercells across western and central Illinois throughout the afternoon hours and extending into the evening,[8] even though the SPC had only issued a slight risk and 5% unhatched tornado forecast for the region.[9] Numerous tornadoes were reported in Illinois, most of which occurred as a result two long-tracked, cyclic supercell thunderstorms. This included an EF3 wedge tornado that caused major damage throughout portions of Taylorville, Illinois, injuring 22 people. At 5:15 PM, a tornado emergency was issued for Central Christian County. A total of 406 homes in Taylorville sustained some form of damage; 66 homes suffered major damage; and 34 homes experienced severe damage or total destruction. An EF1 tornado caused moderate damage in Beardstown, while EF2 tornadoes ripped roofs off of homes near Litchfield and Le Roy. Another EF2 touched down in Stoningon, snapping trees and power poles, and destroying garages before leveling several barns outside of town. Producing 29 tornadoes in the state, this was the largest December tornado outbreak in Illinois history.[10][8] Further south, a secondary area of severe weather produced two EF0 tornadoes in Alabama.[11]

A few isolated tornadoes continued to touch down across the Southern United States on December 2. This included strong EF3 tornado that struck the Naval Submarine Base Kings Bay in Camden County, Georgia, tossing heavy objects and injuring four people. Rare severe thunderstorm watches with an isolated tornado warning were issued as far north as southern Ontario in Canada.[12][13][14] No tornadoes were reported in Ontario; however, a lightning strike sparked a fire at a home near Mount Forest, causing an estimated CA$175,000 in damage.[15]