The F5 That Shouldn't Have Happened

Get Cheat Sheet: https://stormchasercoaching.com/storm-chasing-podcast-notes Join Discord Community: https://discord.gg/stormchasercoaching Get FREE Chaser Safety Ebook: https://stormchasercoaching.com/eight-rules/ Get FREE Dixie Alley Ebook: https://stormchasercoaching.com/dixie-alley/ Buy Merch: https://storm-chaser-coaching.myspreadshop.com/ Follow Twitter: https://x.com/TornadoCoaching Subscribe and Join our Channel Membership: www.youtube.com/channel/UCCP12NYSDa9KL26PW1zokcA On August 28th, 1990, a violent F5 tornado tore through the Chicago suburbs in conditions that shouldn't have produced anything close to that powerful — and the reason why will change how you read the sky forever. Join Gabriel Harbor and meteorologist Trey Greenwood as they break down the hidden storm-scale processes behind the Plainfield F5, revealing practical forecasting and chasing lessons that could help you spot the next tornado that "wasn't supposed to happen." 00:00 Plainfield F5: Tornado That Defied Odds 01:25 Why Plainfield Was Historically Unusual 01:59 Synoptic Pattern: Aug 28, 1990 Setup 02:34 High CAPE, Low Shear Tornado Setup 03:47 Storm-Scale Processes Behind the F5 05:01 Outflow Boundary Tornadogenesis Cases 06:01 Forecasting Lessons from Plainfield F5 On August 28th, 1990, a violent F5 tornado carved a devastating path through the Chicago suburbs, killing 29 people and injuring hundreds more. What makes the Plainfield tornado so extraordinary to meteorologists and storm chasers alike is that the atmospheric environment that day didn't look favorable for a violent tornado at all. With extreme instability but very limited low-level wind shear, the setup typically associated with hail and damaging winds rather than F5 tornadoes, this event defied conventional tornado forecasting logic. In this deep-dive conversation, host Gabriel Harbor sits down with meteorologist Trey Greenwood of Convective Chronicles to unpack the meteorology behind one of the most powerful tornadoes in U.S. history. They explore the large-scale synoptic pattern that day — a classic northwest flow event with an elongated trough and jet streak aloft — and examine why the high CAPE, low shear environment should have precluded significant tornadic supercells. The key lies in storm-scale processes: the Plainfield supercell generated its own outflow boundary, surged ahead of the storm, and then caught back up to it, ingesting critical low-level vorticity along that boundary to produce an EF5 tornado. Trey also draws parallels to a similar 2019 Tahoka, Texas case where the same outflow boundary tornadogenesis mechanism produced a significant EF2 tornado. The episode wraps with practical forecasting and storm chasing lessons — always watch outflow boundaries, never write off a supercell too early, and remember that extreme instability can override weak low-level shear when boundaries are in play. From the Jarrell, Texas tornado of 1997 to the Plainfield F5, history shows that when CAPE is sky-high and a boundary interacts with a supercell, the rules can go out the window.