Well, it figures. When they demolish New York and Los Angeles, it merits a major movie blockbuster – “The Day After Tomorrow.”

Wipe out Chicago, and all we get is a lousy network miniseries. All kidding and Second City insecurities aside, “Category 6: Day of Destruction” (9 p.m. Sunday and 8 p.m. Wednesday, CBS), is pretty lousy, despite a wealth of impressive special effects that end with an image of a completely demolished Chicago skyline.

A note of caution: Reviewers (as is often the case) were sent a preliminary version devoid of many of the final effects. Even so, it’s clear that all the money and muscle went into delivering an awesome fantasy version of the Windy City destroyed by weather calamity. But while the hokey, melodramatic plotlines are altogether different from the ones devised for “Day After Tomorrow,” they’re just as hokey and melodramatic.

As a result, viewers may well enjoy the sick kick of watching Hollywood magicians bit by bit destroy our lovely architecture. The rest of the stuff, from the overly contrived series of human catastrophes to the vague and shallow nod to environmental concerns, is hopelessly juvenile and at times makes this two-part, five-hour epic pretty slow going.

The story line storyline involves a summer of runaway weather in which not one, but two major storms hit Chicago simultaneously. One is a tropical hurricane moving up from the gulf, destroying the St. Louis arch in its path, while the other is an arctic storm descending from the north. The result is a tsunami of tornadoes strong enough to demolish major skyscrapers. While ridiculous (hurricanes are about the only weather horror we’re spared here), that kind of apocalyptic fantasy is a basic tool of disaster fiction.

Where scriptwriter Matt Dorff really errs is in the unwieldy assortment of additional coincidences and ill fortunes he heaps upon the city and his hapless characters.

Evildoers at the fictional utility (Lexer Electric) are woefully unprepared for computer hacking, and thus, just before word of the storms arrives, Chicago is dealt a major blackout like the one the East Coast suffered just over a year ago. As if dual mega-storms weren’t enough, the blackout silences major communications and throws the city into chaos only hours before the first telltale gust.

And, as in “Day After Tomorrow,” the people whose lives we follow endure mishaps and atrociously bad luck. Here’s one: Thomas Gibson, playing an official dealing with the crisis, has a daughter dating a psychopath. When the lights go out, he’s stalking her and her mother at the bank, where the power meltdown causes all the security doors to slam shut. In the skirmish, Gibson’s daughter gets shot and needs to be rescued, just at the time her father is trying to manage a citywide crisis and hospitals have all but shut down.

That’s just a taste of the madness. Meanwhile, a harried secretary of energy (Dianne Wiest) tries to grapple with it all in a political sideshow that’s long on preachy pronouncements and short on dramatic depth or thematic clarity. We’re warned we better do something, but it’s never clear what.

The performances of the large cast, including Gibson, Wiest and Brian Dennehy (as a wizened climactic expert) bring maturity to an otherwise sophomoric undertaking. But they don’t rescue the ridiculous storytelling, and the dramatic credibility in all this proves even less durable than a Loop besieged by countless cyclones.