Great Storm of 1975
Storm system in Central and Southeastern United States in 1975
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Through Tornado, Great Plains and Air mass
Meteorological synopsis
The storm originated over the Pacific Ocean and crashed into the Northwest Pacific coast with damaging gale-force winds on January 8, 1975. By January 9 it had cleared the Rocky Mountains and began to redevelop and strengthen. At the same time, Arctic air was being drawn southward from Canada into the Great Plains, and large amounts of warm tropical air from the Gulf of Mexico were being pulled northward into much of the eastern U.S. The storm was a classic Panhandle Hook which moved from Colorado into Oklahoma before turning northward towards the Upper Midwest. It produced record low barometric pressure readings in the Midwest, with the pressure falling to an estimated 28.38 inHg (961 mb) just north of the Minnesota border in Canada.
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Tornado outbreak
Tornado summary event
An unusual feature of this outbreak was that daytime heating, typically a key ingredient in the formation of tornadoes, had very little impact on their development. Rather, as the storm system pulled out into the central plains, strong thunderstorms and tornadoes quickly began to form despite the late hours. The first two tornadoes touched down after 10:00 p.m. CST on January 9 in Oklahoma and Louisiana. From there the progression of the twisters shifted eastward through the overnight and early morning hours, setting the stage for what would turn out to be a record-setting day on January 10. Texas saw five tornadoes between 1:30 a.m. and 3:30 a.m., one tornado touched down in Arkansas at 6:00 a.m., Louisiana saw seven tornadoes between 5:30 a.m. and 8:00 a.m. (killing one person), Mississippi had five tornadoes between 8:15 a.m. and 10:00 a.m. (killing nine), and Illinois and Indiana each experienced three lunch-hour tornadoes. The tornadic line of storms then shifted into Alabama (killing one) and Florida during the afternoon and evening hours.
Mississippi and Alabama were the two states hardest hit by this outbreak. Alabama had the most twisters of any state with 13, but Mississippi saw the largest and deadliest tornado. An F4 tornado that tore through Pike, Lincoln, Lawrence, and Simpson Counties at 8:14 a.m. killed nine people and injured over 200, and severely damaged 38 blocks in the town of McComb. The 39 tornadoes on January 10 marked the most active tornadic day in January in U.S. history at that time. The 52 tornadoes during January 1975 also set a U.S. record for the most tornadoes during that month. Both of these records were broken in January 1999.
After a calm day on January 11, four more tornadoes touched down in Florida and Georgia on January 12, killing one person in Florida. By the time the outbreak ended it had produced 45 tornadoes, killed 12 people, injured 377 and caused $42 million in damages.
Confirmed tornadoes
Prior to 1990, there is a likely undercount of tornadoes, particularly E/F0–1, with reports of weaker tornadoes becoming more common as population increased. A sharp increase in the annual average E/F0–1 count by approximately 200 tornadoes was noted upon the implementation of NEXRAD Doppler weather radar in 1990–1991. 1974 marked the first year where significant tornado (E/F2+) counts became homogenous with contemporary values, attributed to the consistent implementation of Fujita scale assessments. Numerous discrepancies on the details of tornadoes in this outbreak exist between sources. The total count of tornadoes and ratings differs from various agencies accordingly. The list below documents information from the most contemporary official sources alongside assessments from tornado historian Thomas P. Grazulis.
January 9 event
January 10 event
January 12 event
Blizzard
As the storm system began to move northeastward out of Oklahoma, the cool air pulled down behind the system interacted with the moisture being pulled northward to produce snow over a large part of the Midwest. The snow began falling on Friday, January 10 and continued for the next two days. Snowfall of a foot (30.5 cm) or more was common from Nebraska to Minnesota, with 27 inches (69 cm) in Riverton, Minnesota. The heaviest snow fell to the west of the low pressure center, which tracked from northeast Iowa through central Minnesota up to Lake Superior. Sustained winds of 30–50 mph (48–80 km/h) with gusts from 70–90 mph (110–140 km/h) produced snowdrifts up to 20 feet (6 m) in some locations.
Sioux Falls, South Dakota saw visibilities of below 1⁄4 mile (0.4 km) for 24 straight hours, and just east of Sioux Falls a 2,000-foot (610 m) broadcast tower collapsed. In Willmar, Minnesota, 168 passengers were trapped in a stranded train for hours, unable to walk to shelter because of dangerously low wind chill values. In Omaha, Nebraska a foot (31 cm) of snow fell, Sioux Falls saw 7 inches (18 cm), Duluth, Minnesota saw 8 inches (20 cm), and International Falls, Minnesota saw 24 inches (61 cm).
Record low pressures were recorded in communities in Nebraska, Minnesota, Illinois, and Wisconsin, with a low of 28.55 inHg (967 mb) in Duluth, Minnesota. Approximately 58 people died from effects of the blizzard and over 100,000 farm animals were lost. The combination of snowfall totals, wind velocities, and cold temperatures made this one of the most severe blizzards the Upper Midwest had experienced.
Record events
This storm system had, in part, a large effect on the weather in the entire eastern half of the country. A number of different weather records (at the time) were set during the four days of this storm, especially in daily high temperatures, wind gusts, low barometric pressure readings, and number of tornadoes.
Daily high temperatures
January 10
- Chicago: 60 °F (16 °C)
- Indianapolis, Indiana: 62 °F (17 °C)
- Louisville, Kentucky: 66 °F (19 °C)
- South Bend, Indiana: 61 °F (16 °C)
January 11
- New York City: 65 °F (18 °C)
- Providence, Rhode Island: 61 °F (16 °C)
- Washington, D.C.: 75 °F (24 °C)
Low pressure measurements
- Duluth, Minnesota: 28.55 inHg (967 mb)
- Minneapolis, Minnesota: 28.62 inHg (969 mb)
- Rochester, Minnesota: 28.67 inHg (971 mb)
- Milwaukee, Wisconsin: 28.86 inHg (977 mb)
- Rockford, Illinois: 28.87 inHg (978 mb)
- St. Louis, Missouri: 28.93 inHg (980 mb)
Tornadoes
- Most tornadoes on one day in January: 39
- Most tornadoes in the United States during January: 52