CR Weather Bubble? Were you not alive in 2008 and 2020???
It's effectiveness is not absolute. No weather bubble really is absolute. But ask DM and QC weather nerds - they believe their metros also have a "bubble".
It is indeed there for CR. Far too often this spring and summer, lines of pretty intense storms have approached Linn County and split apart, skirt the northern and southern reaches of the county - only to have the line reform after it passes east. I dunno if it's the heat of the metro or some sort of locational thing as far as how lines/cells of storms cycle through their lifespans.
Who knows really.
Yes, the derecho happened - I sort of chalk that up as it being "too strong to fail" kind of thing. And it wasn't the first derecho to hit CR, too. I've lived at my current near Kirkwood address for almost 20 years now, and I can think of a couple different storms that packed quite the wallop. One did a LOT of damage to the neighborhood just west of Kirkwood Blvd behind where the Kum & Go is now (believe something like 2006-ish). Believe there was one in late July last year too.
But how many tornados can anybody name that truly hit CR proper? I can't name but one back in the 70's I believe, somewhere around the Coe College to Kenwood area of town. But otherwise they seem to skirt both north and south of town. Usually we get 1-2 every year that come close, but miss. There's been a couple weak ones recently that skirted the Kirkwood area that touched down around the C St SW/Ely Road area. One was not too long ago in June I believe, maybe late May? The other was the cell remnants of that fluke January cold core storm (the "Williamsburg tornado") that I believe was last year?
Saw both of those myself - hell, the January 2023 one, I saw the funnel cloud form literally right above my home. Both were weak as far as tornados go, but they did indeed touch down very close to CR proper.
Otherwise, though...nada. I don't remember specifically any recent (say 1990's to now) confirmed tornado that hit CR at all.