The tornado outbreak of February 28 – March 1, 2017 was a widespread and significant outbreak of tornadoes and severe weather that affected the Midwestern United States at the end of February 2017 and beginning of March. Fueled by the combination of ample instability, strong wind shear, and rich low-level moisture, the event led to 71 confirmed tornadoes and thousands of other non-tornadic severe weather reports. The most notable aspect of the outbreak was a long-tracked EF4 tornado—the first violent tornado of 2017 and the first violent tornado during the month of February since the 2013 Hattiesburg tornado—that tracked from Perryville, Missouri to near Christopher, Illinois, killing one person. Three EF3 tornadoes were recorded during the event, including one that caused two fatalities in Ottawa, Illinois, one that caused a fatality near Crossville, and one that heavily damaged or destroyed homes in and around Washburn. In addition to the deaths, 38 people were injured by tornadoes and an additional 30 were injured by non-tornadic impacts, mainly by fallen trees.
Meteorological synopsis
The first indications of a severe weather event came on February 24, when the Storm Prediction Center (SPC) issued a threat area across Arkansas and portions of the lower Mississippi Valley valid for February 28. The threat level was maintained for Arkansas and surrounding states in the subsequent outlook, while a new risk area was introduced from northern Louisiana to southwestern Kentucky valid for March 1. Despite significant variance among model guidance, the SPC issued a day 3 Enhanced risk over the Ozark Plateau into southeastern Missouri, encompassed by much broader Slight and Marginal risk areas. The next day, an Enhanced risk was introduced portions of the Mid-South and Ohio River Valley in anticipation of a widespread damaging wind event on March 1. On February 28, the SPC introduced a Moderate risk of severe weather across portions of eastern Missouri, central and southern Illinois, central and southern Indiana, into western and northern Kentucky. The organization warned of supercell thunderstorm development and the potential for "nocturnal significant tornadoes." As the storm system spread east on March 1, a Moderate risk was briefly added across central Kentucky and middle Tennessee into the Cumberland Gap. The setup for a widespread tornado outbreak came as a mid- to upper-level trough progressed eastward from the Great Basin and lower Colorado River Valley to the Mississippi Valley on February 28. With large-scale height falls, three rounds of severe weather were expected to evolve across the Midwestern United States: elevated thunderstorms across northern Illinois early in the day, significant supercell development throughout the evening and overnight hours, and a quasi-linear convective system throughout the overnight hours into March 1. At the surface, an area of low pressure developed near the Missouri–Iowa border and progressed into southern Michigan late on February 28. A cold front, meanwhile, extended from the Plains to the Mississippi Valley, and a warm front lifted northward across Illinois. In the warm sector ahead of the cold front, rich low-level moisture surged northward, with dewpoints of observed across Texas and Louisiana. Although a strong subtropical jet stream allowed a widespread cirrus plume to overspread the risk area, limiting surface heating in some locations, mid-level CAPE values were still expected to reach upward of 1500–2000 J/kg. Combined with ample moisture, steep mid-level lapse rates, and sufficient destabilization, effective bulk shear near or over , was expected to yield storm relative helicity values in excess of 300–400 m2/s2. However, the driving mechanism for convection across the risk area was still somewhat uncertain given the confluence of a weak capping inversion, warm-air advection, and negligible ascent.
The first signs of convective activity came around 19:45 UTC, when shallow cumulus development was observed across Arkansas. A half hour later, at 20:15 UTC, the SPC issued their first tornado watch across portions of Kansas, Missouri, and Illinois, the first of many watches issued throughout the afternoon and overnight hours. The first significant tornado touched down at 22:41 UTC, causing extensive damage along a path from Naplate to northwest of Marseilles, Illinois, most notably the city of Ottawa, with that tornado being rated EF3. There, two deaths were recorded and fourteen people were injured. Two other EF3 tornadoes were documented during the outbreak: one near Washburn, Illinois, and the other from Crossville, Illinois to Oakland City, Indiana that caused one fatality as well that traveled 44 miles and was produced by the same supercell as the Perryville tornado. The strongest event was an EF4 tornado that traveled more than from Perryville, Missouri to southwest of Christopher, Illinois that killed one person, making it the first violent tornado of 2017, and the first since an EF4 tornado struck near Chapman, Kansas on May 25, 2016. In total, 72 tornadoes were confirmed during the outbreak. This outbreak would be followed by another outbreak which affected many of the same areas only 5 days later.
Confirmed tornadoes
February 28 event