It Could Happen
by: Pat Hernandez, May 25, 2011 5:05:00 pm
Governor of Missouri Jay Nixon talking to residents of Berkeley, Missouri while surveying damage from an EF4 tornado that hit on the previous night. Taken by the Missouri Department of Public Safety.
TV News anchor: "Chance, are you still seeing a tornado?"
Reporter: "It's still on the ground, we driving right in front of it."
Female TV News anchor: "Yeah, velocity is looking rather impressive, Rick."
This week, television stations in the Oklahoma City area and SW Missouri have been busy covering a series of tornadoes. The country's midsection remains at risk for severe weather that can produce even more violent twisters. But don't expect that type of activity in the Houston area anytime soon.
Scott Overpeck is with the National Weather Service in Alvin. He says the souped up environment capable of producing tornadoes has been confined way north of Houston and further. There are four ingredients that combine to produce tornadic conditions.
"Look for a lot of moisture which, being close to the gulf of Mexico, that's not usually a problem for us. Instability, where you have air that can rise on its own when it's lifted, and typically you need a front, or some type of upper level disturbance that comes across in the jet stream."
The unstable air must be lifted, and that is done with a front or an upper level disturbance that comes across in the jet stream. The fourth ingredient...strong winds that are changing in direction and in the increasing height in the atmosphere. Overpeck says the jet stream has been farther north toward Oklahoma, interacting with the other ingredients to produce volatile conditions.
"If the jet stream was a little bit farther south, and we had a couple of these disturbances coming to our area, then I think we would see those conditions come together for the possibility of severe storms and tornadoes in our area. But because of the position of the jet stream, and the way these systems have been coming across the country, that's why we have not seen the activity here."
Fred Schmude is storm watch manager with Impact Weather. He says usually this time of the year, the main storm track is located too far north of the Houston area, across the central plains and Mississippi Valley, and away from the warm Gulf air.
"Typically for tornadoes to form, you need the warm moist air interacting with the jet stream dynamics. That jet stream dynamics is what produces the air that causes it to turn, and you need the interaction of that, and that warm moist air to produce the thunderstorms that can produce tornadoes."
The last time that happened was in November of 1992, when a cluster of twisters including an F4 tornado, struck the Channelview area east of Houston. Winds estimated at 200 mph wiped some homes off their foundation. Schmude says it's during the late fall early spring that the jet stream moves far enough south to make this area more susceptible to tornadoes.