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Tornadoes: A welcome twist

After two devastating years, tornado season has been a quiet one, although that's about to change.

Tragically, this week's Texas tornado outbreak was blamed for six fatalities, yet perhaps surprisingly that was far and away the deadliest outbreak of 2013.

From Jan. 1 through April 30, only three U.S. tornado fatalities were recorded, compared with 66 in the same period last year, and a shocking 365 during the incredible 2011 season, according to the Storm Prediction Center.

For the first four months of this year, the preliminary tornado count stands at 232, and that number almost certainly will decrease as double-sightings get filtered out. For example, the preliminary count for January, 87, has been reduced to 75.

By comparison, the final numbers for the first four months of 2012 came in at 496, and for 2011, 912.

What's different about this season?

One big factor might have been the general coolness of March, said Harold Brooks, senior scientist at the storm center, and when it's cooler, tornadoes tend to be fewer.

April gets a bit more complicated. "There's not really a temperature signal," said Brooks. But last month the upper-air patterns across the nation was unfavorable for twisters.

The pattern was characterized by higher pressure in the West and lower pressure in the East, and it consspired to shut off the Gulf of Mexico moisture supply, a critical ingredient for atmospheric volatility.

How long will this continue?

"That's going to change this weekend," said Brooks. Strong storms are possilble from the Dakotas to the Oklahoma-Texas border. "We've got a pretty good system coming up."

Brooks said the tornado count for the next 90 hours might match that of the last 90 days.

As for our region, where things have been in the quiet side, thunderstorms are possible on Monday.