When the National Weather Service issues a tornado warning — as it did for Allegheny County just a few minutes ago — that means one of two things has happened: someone has actually spotted a funnel cloud and reported it, or NWS meteorologists have seen something ugly on the radar.

Here’s what they’re looking at:


That’s a cap from the NWS taken a couple minutes ago. This isn’t the radar we see on TV; it’s called storm relative velocity, and it shows the forecasters how the air is moving in relation to their radar. The red returns, in general, are moving towards the local NWS station, in Moon Township; the green returns, in general, are moving away. The brighter the colors, the faster the air is moving.

You can see a couple things in this shot. First, the whole storm is rotating; you can tell by how the green has wrapped around the bottom of the red blob in northern Washington County. That’s an indication of a pretty strong storm.

But that red splotch in south-central Allegheny County is the one that prompted the tornado warning. That shows the NWS folks there is a tight area that is rotating rapidly; if it hasn’t already produced a funnel cloud, it could at any time.

We have access to all this stuff, if you’re as interested in the weather as Weather Freak Boy is. The NWS Pittsburgh home page is here; click on the radar bottom of the page and you’ll find a whole mess of different radars, all of which include loops and the ability to zoom on a particular spot, in the menu on the left side of the page.

Or, you could just huddle in the basement. Which is probably what Weather Freak Boy should be doing right now.


  1. I geek over any severe weather and I think that has to do with growing up in Erie where we had 4 seasons in a day and always watched the snow. I think its in our blood

    I was glued to KDKA’s coverage all night and watching the Vipr

    yeah i love this stuff


  2. Okay, add me to the weather geek list too. I was glued to the TV and to a weather radar program on my computer. Then I was mesmerized by the rotating clouds outside all the while listening to the police scanner to hear what was going on. Basement? What basement?!?


  3. It runs in the family….I check the Ntl. Hurricane Center’s website daily now, and if there is something looming, I check it every update (which I know is every three hours)

    I hope everyone made it out of this one okay.


  4. It’s great to know I’m not alone. :) Is everyone ready for tomorrow’s predicted storms?!?


  5. I don’t know about Doogle’s Erie comment (I grew up there, too). I mean, I only check the weather — if I even bother — to see how I need to dress the girls. What warnings? ;)

    Although we did, easily, have four seasons in one day.



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