For the second time this month, a rare event became less rare as severe storms raced across town, dumping heavy rain and dropping funnels that made several tornado touchdowns. At the time I write this, at least four tornadoes have been confirmed and after the damage surveys are conducted, there will likely be more. A line of strong storms began to impact Washington county just before 9 am, spawning tornadoes in Somerville and downtown Brenham, flipping cars and damaging roofs. That line then drifted into Madison, Walker and Waller counties where two more twisters hit damaging buildings.
A second line developed along I-10, and a rotating storm headed for Pearland, where several eyewitnesses reported a funnel touching down. It ripped the roof off a gas station and punched holes in the roofs of several businesses. This storm was captured on HD Doppler. The yellow tube represents the rotating storm as it moved toward FM 518 and Highway 35:
Analyzing the storm structure, HD Doppler shows the rotating winds coming toward the radar (green) next to winds moving away from the radar (red). To get the estimated amount of shear (a measure of the strength of the rotation), we add the two numbers together and ignore the sign. In this case, the shear is at least 45 mph, but that's just and estimate of the winds. Remember that's what the beam can see at a height of several thousand feet. The actual winds closer to the ground are higher.
In addition to the tornadoes, blinding rain fell in a short period of time causing flooding. Thankfully, the storms didn't last as long as they did just a few weeks ago, so the waters receded quickly. However, quite a few roads and streets became rivers stranding motorists who tried to test them. Bush Airport set a daily rainfall record of 2.80" and Hobby picked up nearly an inch, also a record. On this estimate of the totals from HD Doppler, notice the areas of dark green that outline the path of today's storms. That's where the highest amounts of 2"-3" fell:
The National Weather Service will conduct damage surveys to classify the strength of today's twisters, but based on the damage I've seen, they will likely fall at the low end of the Enhanced Fujita Scale. Probably EF0 or EF1 with winds ranging from 65-110 mph. Check back tomorrow for updates on these as I get them.