Blog Article
Severe Clear: The Sky on 9/11 vs. Today's Weather
25 years after 9/11's famous 'severe clear' sky, we break down the meteorology behind that term and how this weekend's storms and flood risk affect college football and NFL openers.
Severe Clear: What the Sky Looked Like 25 Years Ago, and What It Looks Like Now
Alright folks, today's a heavy one. Twenty-five years since September 11, 2001, and if you've been anywhere near a TV or a news feed today, you've heard the phrase pop back up: severe clear. Pilots used it that morning to describe the sky over the Northeast. High pressure, bone-dry air, visibility for miles and miles. It's become shorthand for a certain kind of American memory. A perfect blue morning that turned into the worst day a lot of us can remember.
So let's talk about what that phrase actually means, meteorologically, and why it matters that today's sky doesn't look anything like it.
What "Severe Clear" Actually Means
Here's the thing. "Severe clear" isn't an official NWS term, it's pilot slang, but it describes something real. A strong area of high pressure had settled over the Northeast in early September 2001. High pressure sinks air. Sinking air dries out and suppresses cloud formation. Pair that with a dry Canadian air mass pushing in behind a cold front, and you get dewpoints in the 40s, near-zero humidity by afternoon, and visibility that pilots that day described as 60-plus miles. You could see the curvature of the horizon from altitude. That's not poetry, that's just physics. Dry air scatters less light and holds no moisture to fog up your view.
It's the same setup we talk about anytime a cold front clears out humidity and leaves you with one of those crisp fall mornings where the sky looks painted on. Good weather, plain and simple. Which is part of why that day sticks with people the way it does.
Today's Atmosphere Is a Different Animal
Contrast that with where we sit tonight. This week has been anything but severe clear. Just yesterday, training thunderstorms dumped almost 7 inches of rain on Gallipolis, Ohio, and Point Pleasant, West Virginia, triggering water rescues and closing US-23 in Pike County. A mesonet station near Colby, Kansas, clocked an 87 mph thunderstorm gust. That's the kind of active, moisture-rich pattern we've had for going on two weeks now, stacked right on top of Tropical Storm Edouard's flooding in Texas and Hurricane Lowell brushing Hawaii earlier this month.
Tonight, SPC has a Slight Risk for severe storms up in northern Minnesota, Duluth to Bemidji, with large hail and a couple of tornadoes possible, and a broad Marginal Risk stretching from Charlotte and Nashville down through Atlanta and out to Omaha. None of that is severe clear. It's the opposite: a moist, unstable air mass getting squeezed by a cold front.
The Weekend Forecast Behind the Games
Speaking of that front, it's going to be a character in this weekend's sports storylines whether anybody mentions it on the broadcast or not. Saturday's college slate is loaded, and a few games sit right in the path of what SPC and WPC are watching. Kansas State hosting Washington State in Manhattan sits inside Saturday's Marginal severe risk zone across the Central Plains, where hot, unstable air south of the front could fire up isolated large hail and gusts over 60 mph by evening. Pitt hosting UCF in Pittsburgh and the Temple-Penn State game in Philadelphia both sit under a WPC Slight Risk for excessive rainfall Saturday into Sunday, part of a corridor running from the Ohio Valley through the Mid-Atlantic that's already sitting on saturated ground from Thursday's flooding.
That same soggy setup carries into Sunday's NFL openers. The Eagles hosting the Commanders in Philadelphia, and to a lesser extent the Panthers-Bears game in Charlotte, fall inside that same flash-flood-aware zone stretching up the I-95 corridor. Nothing here screams cancel your tailgate, but if you're headed to Manhattan, Kansas, or you're tailgating in the Ohio Valley, keep an eye on the radar Saturday afternoon and have a rain plan for Sunday. Nashville's game against the Jets sits closer to seasonal norms, high near 84, low near 62 this time of year, so that one should play out more comfortably.
Norbert Keeps the Pacific Busy
One more thread worth a mention, because it ties right back to two weeks of tropical headlines out of Hawaii. Tropical Storm Norbert is spinning in the East Pacific, several hundred miles southwest of Baja California, with 63 mph winds. The current track keeps it well south and west of the islands, and NHC's forecast shows it weakening as it approaches its closest pass to Hawaii Island late next week, more than a thousand miles out. After Hurricane Lowell's brush with Kauai earlier this month knocked out power to over 33,000 customers, Hawaii's kept one eye on the tropics all September. Norbert doesn't look like a repeat of that, but it's a reminder the Pacific isn't finished with this pattern yet.
The Takeaway
A clear sky doesn't mean a calm world, and a stormy pattern doesn't mean disaster either. That's the whole lesson buried in a day like today. Twenty-five years ago, the sky was about as perfect as the atmosphere gets, and it had nothing to do with what happened next. Tonight, the sky's doing what September skies do this year: throwing storms at the Plains, soaking the Ohio Valley, and keeping an eye on a tropical system nobody in Hawaii wants to think about again so soon. Watch the front, plan your tailgate around it, and take a minute today for what the calendar's actually asking us to remember.