Despite the calendar reading early October, tornadoes inflicted heavy damage in parts of Nebraska, South Dakota and Iowa on Friday, Oct. 4.
Severe Weather Expert Dr. Greg Forbes says 12 tornadoes have been confirmed from northeast Nebraska into southeast South Dakota and northwest Iowa. National Weather Service meteorologists will continue storm surveys to determine the final tornado count, as well as Enhanced-Fujita ratings.
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The majority of the tornadoes were spawned by two supercells, which you can see in the animated radar history below at right.
Supercell #1: Wayne, Neb. to Plymouth Co., Iowa
Animation of radar with preliminary tornado reports (red tornado symbols) during the evening of Oct. 4, 2013 in northeast Nebraska and northwest Iowa.
The first supercell spawned its first tornado, a brief "rope" near Stanton, Neb. around 4:30 p.m. CT. Just one hour later, that supercell spawned another tornado which produced significant damage on the east side of Wayne, Neb. Fifteen were injured in initial reports. This tornado also destroyed a farm house and an airport near the town.
Less than half an hour later, a multi-vortex tornado was spotted in neighboring Dixon County, Neb. to the northeast of Wayne from that same supercell. The tornado, at the time, was estimated to be a half-mile wide.
After damaging at least one home near North Sioux City, S.D., this supercell crossed into Plymouth County, Iowa, with at least one report of a one-half to one-mile wide tornado west of Hinton, Iowa.
- Time from first to last tornado report: 2 hours, 49 minutes
- Distance supercell traveled while producing tornadoes: About 75 miles
- Notable tornadoes (& ratings) from this supercell: EF4 in Wayne, Neb., based on damage to the industrial park. Two EF1s (100-110 mph winds) near Jefferson, S.D. Another EF1 (100-110 mph winds) near McCook Lake, S.D. (more to come as surveys continue)
- Historical analysis: The EF4 tornado in Wayne is rare for October. The last F/EF4 or stronger tornado in Nebraska was the massive Hallam, Neb. tornado on May 22, 2004, according to the NWS office in Omaha. The last October F/EF4 or stronger tornado anywhere in the U.S. was on Oct. 3, 1979 in Connecticut.
Supercell #2: Macy, Neb., Woodbury and Cherokee Counties, Iowa
Nine minutes after the first supercell spawned tornado hammered parts of Wayne, Neb., a second supercell began its two-hour rampage.
After spawning a brief tornado near Lyons, Neb., it then swept into the town of Macy, Neb., destroying at least six homes and damaging 12 others.
Crossing the Missouri River, the tornado in Woodbury County, Iowa was observed to be one-mile wide near Sloan, and east of Moville, Iowa, with damage reported in both locations.
Continuing northeast into Cherokee County, major damage was reported in the town of Quimby.
- Time from first to last tornado report: 2 hours, 1 minute
- Distance supercell traveled while producing tornadoes: About 70 miles
- Notable tornadoes (& ratings) from this supercell: A tornado from near Climbing Hill to near Washta, Ia. produced EF4 damage south of the town of Pierson, including tossing farm equipment over 400 yards. Peak winds were estimated at 170 mph. The maximum path width of this tornado was up to 1.5 miles wide. Another tornado from Macy, Neb. to Sloan, Ia. was rated EF2.
A Close Call
While recognizing the damage these tornadic supercells were responsible for, we should point out a close call.
Sioux City, Iowa, with a 2010 population of about 82,000, is the most populous city in the area affected.
The twin supercells on Oct. 4, 2013, one spawning a multi-vortex tornado, the other a mile-wide tornado, thankfully missed the city to the north and south.
Unusual for October?
Of course, the very nature of averages smooths out anomalous, extreme events. Any time warm, humid air near the surface clashes with cool, dry air aloft -- especially when sufficiently strong wind shear is present, particularly in the lowest levels of the atmosphere -- tornadic supercells can result.
While certainly not unprecedented, October tornadoes in this part of the nation are relatively infrequent.
These are the first October tornadoes in Nebraska since Oct. 19, 2001 and in Iowa since 2007.
Prior to this event, there had been 75 October tornadoes in Nebraska and 13 in Iowa since 1980.
The only other F/EF4 or stronger October tornado in Nebraska history was on Oct. 29, 1956. The Cornhusker State is the only state with more than one F/EF4 October tornado in modern records, according to NWS-Omaha.
Similarly for Iowa, the only other October F/EF4 or stronger tornado in records dating to 1950 was an F5 tornado on Oct. 14, 1966.
The Hawkeye State had been in a relative tornado drought during the past few years.
According to the National Weather Service Office in Des Moines, Iowa set a modern-era record low tornado count in 2012, with only 16 tornadoes statewide.
This year hasn't been much more active, thankfully, with only 15 Iowa tornadoes, prior to the Oct. 4 event. Those 15 tornadoes were also contained within a 38-day period from May 19 through June 26, the shortest such period on record prior to the Oct. 4 tornadoes, according to NWS-Des Moines.
The intensity of the Wayne, Neb. and Pierson, Ia. EF4 tornadoes is also unusual for October anywhere in the country. Severe weather expert Dr. Greg Forbes says they were only the sixth and seventh violent October tornadoes – a tornado rated 4 or 5 on the original or enhanced Fujita Scale – nationwide since reliable tornado records began in 1950.Follow @wxjerdman
MORE: Nebraska/Iowa Tornado Damage Photos
This photo shows damage from a tornado, Saturday, Oct. 5, 2013 in Wayne, Neb. As many as nine tornadoes hit an area covering northeast Nebraska and northwest Iowa, causing structural damage and injuries but no fatalities, the National Weather Service said Saturday. (AP Photo/Nebraska State Patrol)