Texas assesses tornado damage

Residents in the southeast suburbs of Houston were picking up the pieces Wednesday after a strong tornado tore through neighborhoods the previous afternoon. Meanwhile, the threat of severe weather shifted to the Southeast, with a continued risk of strong to damaging winds and isolated tornadoes in southern Virginia, the Carolinas and Georgia.

The conditions Tuesday favored dangerous thunderstorms but only along the immediate Gulf Coast.

One tornado struck Pearland and Pasadena, Texas, before intensifying as it moved northeast, prompting the National Weather Service’s Houston-Galveston office to issue its first “tornado emergency.” Meteorologists warned that the tornado, which was already ravaging structures, was “large and extremely dangerous.”

The Weather Service has confirmed at least EF2 damage – corresponding to winds in the range of 111 to 135 mph or greater – though survey crews were still combing through the damage path for clues to confirm the tornado’s intensity.

The storm system also brought heavy downpours. Houston picked up 4.04 inches of rain, more than 3.5 inches of which fell in just two hours. That makes it the second-wettest January day on record at Houston’s George Bush Intercontinental Airport, where bookkeeping dates to 1969.

Meanwhile, tornado watches were issued in the Florida Panhandle with the possibility of expanding farther east. Severe weather was expected to close in on the Interstate 95 corridor during the evening, with storms pushing offshore before midnight.

It has been an exceptional January for severe weather. A staggering 159 preliminary reports of tornadoes have been received, with nearly a week left to go in the month – 16 stemmed from Tuesday’s swarm of storms. A typical January averages three dozen twisters over the Lower 48.

On Tuesday, a Level 3 (out of 5) “enhanced” risk of severe weather stretched from south of the Matagorda Peninsula in Texas to the Mississippi Delta and Florida Panhandle. The Weather Service warned of a “conditional” risk for strong tornadoes. While instability, or “juice” for storms, was meager, that limited buoyancy was offset by robust shear – a change of wind speed and/or direction with height.

Thunderstorms weren’t expected to blossom to particularly great heights, but any clouds that spanned multiple layers were encouraged to rotate. This was especially true along the warm front itself, where storms were able to ingest more concentrated stream-wise vorticity, or horizontal twist, which then was tilted onto a vertical access.

That gave one thunderstorm cell south of Houston a bit of a boost during the midafternoon. A kink of rotation developed near Pearland around 3:15 p.m. and quickly went on to produce a tornado. Then that circulation swung northeast as a second area of spin developed a few miles to its north. At least two areas of rotation were present simultaneously, and it’s possible that two tornadoes may have been on the ground at the same time briefly.

It then appears that the vorticity, or spin, of both circulations merged east-northeast of Pearland, somewhere near the intersection of Interstate 45 and the Sam Houston Turnpike.

That then grew into a serious tornado, which spurred the Weather Service to issue a dire tornado emergency for places along Route 330 between Baytown and Interstate 10 near McNair.

It was the first time the Weather Service in Houston had done so. Debris was lofted more than 10,000 feet into the air.

“Came back from a week of leave to issue my first, and office’s first, tornado emergency,” tweeted Jimmy Fowler, the forecaster on duty at the Weather Service in Houston during the storms. “Kind of a blur and maybe blinked a total of 8 times all shift.”

A few additional tornadoes spun up in the Golden Triangle along the Texas-Louisiana border.