A Wrap Up of the 2018 Tornado Season (and a Picturesque Tornado in Laramie, Wyoming)

The 2018 tornado season was off to a slow start. One hundred forty six tornadoes in April compared to the 214 in 2017, 166 in May (291 in 2017, 381 based on the 3-year average), 166 in June (146 in 2017), and 94 in July (81 in 2017).  Tornadic activity peaked in late June. Surprisingly, some of the top ten tornado days of 2018 were in April, February, and March, respectively. More tornadoes were reported in Iowa (51), Louisiana (49), and Alabama (42) than other states. There were 10 EF3 tornadoes, but no EF4’s or EF5’s to report. KanSas and Oklahoma went tornado-free from January through April. This has happened only three times since 1950.  As of early June, there were 13 reports of tornadoes in Wyoming, compared to 10 in Oklahoma, usually a prime tornado hotbed.

During the evening hours of June 6, a low precipitation (LP) supercell thunderstorm spawned a long-lived EF3 tornado near Laramie, Wyoming at 5:43 MDT. The tornado covered a path approximately 12 miles long and was on the ground for a total of 53 minutes. Damage surveys conducted by the National Weather Service Cheyenne office (tornado intensity/wind speeds are estimated afterwards based on the amount of damage that has occurred) found grass scoured out in a trail 1/3 of a mile wide and power poles snapped at 90 degree angles along County Road 121, consistent with EF3 damage (estimated maximum wind speeds of 150 mph). The same supercell produced a satellite EF2 tornado (winds up to 120 mph) that damaged an attached garage.  A weak EF0 was confirmed later that night in southwestern Nebraska.

While tornadoes aren’t unusual in Wyoming, they typically occur in low population areas and cause little damage. In previous years, tornadoes over open land may have gone unreported. Furthermore, EF3 tornadoes in Wyoming are quite rare (there have only been 9 instances of EF3 or greater tornadoes in Wyoming since 1950). The Laramie WY tornado was the second EF3 tornado since 1987. Less than a week earlier (on June 1, 2018), an EF3 tornado damaged a subdivision in Gillette, Wyoming (in the northeast part of the state). The recent July 28th tornado in Douglas, Wyoming making a 3rd EF3 for the year.

The early part of the year started off as active, but the combination of a slightly positive ENSO, a negative PDO, and a shift to a positive Northern Atlantic Oscillation- NAO (https://www.globalweatherclimatecenter.com/severe/altering-characteristics-of-tornadogenesis-the-impact-of-global-climate-change-spring-2018-outlook-photo-credit-noaas-national-severe-storms-laboratory) allowed for an extension of drier, cooler Canadian air, keeping the moist Gulf of Mexico air at bay and springing up drought conditions across the Plains (also a feedback mechanism).  Generally, these kinds of blocking patterns are “weaker”, and thus, pretty short-lived (on a timescale <10 days or so). But, depending on the blocking pattern, it can persist for weeks or more at a time. Some slight ridging over the southeastern United States pushed the pattern more northward, leaning towards more high plains action this year.

Unfortunately, 4 tornado deaths were reported this year, but that is down from the 35 deaths in 2017. While this may be attributed to the lack of severe weather, meteorologists say continual public awareness of natural disasters has aided in fewer tornado deaths this year. While tornado “season” may be over, the potential exists for another round of severe weather in southeast Wyoming this weekend.

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©2018 Meteorologist Sharon Sullivan