A few days back the great Alan Melson, KERA's director of interactive, directed his Facebook friends to a great weather-geek (said with all due respect) site where folks are currently having a great debate about whether or not signs point to an icy deep freeze headed toward North Texas toward the middle to end of the month. Alan follows along, he tells me, because it's fascinating stuff thrown out there by meteorologists and other would-be weather forecasters. Says he this afternoon: "A couple posters there called the ice storm on Super Bowl weekend last year, a week or two in advance." So there's that.
Anyway. A few minutes ago the National Weather Service's Fort Worth forecasters posted that graph you see above, along with the note that "when the AO index is positive, Arctic air usually stays bottled up in the Arctic region, but when it turns negative the Arctic air can move farther south and at times invade North Texas." And, as you can see, the index turns negative round the middle to end of the month. Maybe.
I called Dennis Cavanaugh, a meteorologist out of Fort Worth's NWS offices, for further info since, you know, their official look-see far ahead jibes with what Alan's friends have been saying for a few days now.
"From our forecast perspective, we look at the next seven days," Cavanaugh tells Unfair Park. "That's as far as we forecast, so for the extended we look more to climate signals, like the Arctic Oscillation Index." That sound you hear in the background? He just triggered The Band Name Alert™. Sorry ... do go on.
"When it becomes negative it's talking more about the availability of cold air north of us," he explains. "In order for us to get a cold weather outbreak, cold air has to be present somewhere, and the AO going negative after the 12th suggests cold air will be present for North America and for the central-eastern portions of the country. This means there's a potential for cold air. Whether that means we will get cold air or not, that's something we wouldn't know till seven to 10 days out. For the cold air to move into North Texas we'd have to have a fairly strong low pressure system drag the cold air into North Texas, and it may not even exist now, or it may be in place somewhere on the other side of the world and at this point we're not aware of it."
He says: If you'll note the graph, it shows the AO took a downward dip at the end of October. "At the same time," he says, "a cold front came through, and highs dropped from the 80s to the 60s. It brought our temperatures well below normal."
So, then, you're saying it's possible, just not probable. Not yet, anyhow.
"There's the potential," Cavanaugh says. "As for the likelihood? It's just like if you're in a drought: It will continue to persist unless you have available moisture, and if you have available moisture it doesn't mean it's going rain. But it's one of the conditions you need for rain. For us to get a cold-air outbreak it has to be present somewhere. It won't develop out of nowhere. And right now it looks like it will be present."