This morning, Houston, Texas saw one crazy flooding event. Many areas saw upwards of 6 inches of rain in less than an 8 hour period, with rain falling in the 1-2″ per hour range at times.
— Chris Bianchi (@BianchiWeather) January 18, 2017
Rain began in the early morning hours in the Metro of Houston. This rain formed in a very favorable environment for it. There is currently a fairly strong, closed mid and upper level low centered across northern New Mexico. Associated with this is a jet streak that was placed where the Houston area was within the exit region of that jet streak, a favorable region for upward motion.
In addition to this, the atmosphere in place is anomalously moist there. Dewpoints in the Houston region are well into the 60s, with precipitable water (PWAT) values in the region well above the 90th percentile. The closest sounding site to Houston is Lake Charles, Louisiana, and they measured a PWAT value of 1.51″ at 12z this morning, which would be a record for that time on this day.
To top it all off, dewpoints at 850 mb (about 5000 feet off the ground or 1.5 km) are near 12°C, which is a high number for this time of year. The atmosphere in the region was very primed for a heavy rainfall event, with anomalous moisture in place. Combine that with favorable atmospheric dynamics, and a surface boundary in the region, and the set up was perfect.
And this dumped rainfall, causing major flash flooding across the city. Check out some of the scenes across the city.
— KPRC 2 Houston (@KPRC2) January 18, 2017
— DrJimFox26 (@DrJimFox26) January 18, 2017
— Brett Birkinbine (@Birkinbineabc13) January 18, 2017
— ABC13 Houston (@abc13houston) January 18, 2017
Oh yeah, and there were tornado warnings in the city last night. It was a very wild overnight period in H-town. This event reminds me a lot of an August event back in 2008 in Louisville. The city received upwards of 7 inches of rain in 3 hours, with rates in the 8.80″ per hour range. And there were reports of severe weather in Louisville that day, as well.
That event was highly, highly anomalous, but it was in August! This Houston event was in January! We have seen a lot of rain lately, but luckily, not like that.