Houston under severe thunderstorm watch until 11 a.m.

Good morning. The very heavy rain stayed well to the north of Houston during the overnight hours, with 1 to 10 inches falling across east Texas, generally increasing from Conroe north through Shreveport (there’s a flash flood warning in effect for parts of San Jacinto County, East Central Montgomery County and Polk County). Areas in East Texas such as Henderson and Marshall were hit especially hard.

So far a capping inversion has held over Houston, to keep most of the metro area high and dry. However there’s one more round of heavy storms off to the west of Houston that will likely break this cap as it moves through later this morning. As a result the entire region is under a severe thunderstorm watch through 11 a.m.as this system moves toward Houston.

The entire Houston metro area is under a severe thunderstorm watch through 11am today. (National Weather Service)
The Houston metro area is under a severe thunderstorm watch through 11am. (National Weather Service)

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Good start to the evening, but still some concerns for early Saturday

The concern about the potential for heavy rains and storms this evening appears to have been overblown as storms have remained well to the north of the Houston area. Although moisture levels are high, there just hasn’t been enough of an impetus to spur shower and storm development over southeast Texas.

TONIGHT

Given the quiet radar trends I think we can have some confidence that we won’t see the development of widespread rain showers over the Houston region through at least about midnight. That doesn’t mean we won’t see some isolated storms, including the potential for severe weather such as a tornado or two, but I don’t see the very heavy, widespread rain we were concerned about earlier. This is very good news because it cuts down on the potential for extremely high rainfall totals during this event.

Radar as of 7:15pm CT on Friday night. Storms have so far developed north of Houston. (Intellicast)
Radar as of 7:15pm CT on Friday night. Storms have so far developed north of Houston. (Intellicast)

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Strong storms, and potentially major flooding, possible in Houston tonight

Houston faces a significant rain threat later today and during the overnight hours, and the recent forecast model trends are concerning. I think there are two main threats we must consider: the potential for severe weather, and, separately, very heavy rains.

SEVERE STORMS

Much of the Houston region falls into the “slight” risk of severe weather for tonight from NOAA’s Storm Prediction Center. I believe this may undersell the risk a little bit.

Severe weather outlook for Friday and Friday night. (NOAA)
Severe weather outlook for Friday and Friday night. (NOAA)

 

One of the variables forecasters look at when trying to gauge the possibility of severe weather is helicity, which is essentially a measurement of rotation in the upward drafts of a storm system. The greater this value, the higher the threat of tornadoes and damaging winds.

For example, the latest run of the NAM model shows some very high helicity values over much of the northern and northeastern part of the Houston metro area for late tonight. Note that values above 400 allow for the possibility of tornado formation.

NAM model helicity forecast for 2am CT Saturday morning. (Weather Bell)
NAM model helicity forecast for 2am CT Saturday morning. (Weather Bell)

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Houston faces additional flooding concerns this weekend

Good morning. After another day or so of quiet weather we’re going to have to face another period of potentially heavy rain on Friday night and Saturday.

TODAY

Houston will see warm temperatures on Thursday, but how warm depends up the extent of cloud cover. If we’re mostly sunny temperatures could rise into the upper 80s, to near 90 degrees. If there are some clouds, or a scattered shower near where you live, temperatures will probably remain in the mid-80s. In either case, it will be a warm, almost-summer-like day.

FRIDAY

After a slight chance of showers and thunderstorms developing to the north of Houston on Thursday night and Friday morning, we’ll see better rain chances later in the day. It is possible we’ll see some thunderstorms move in from the west later on Friday, during the evening hours. For now the west-northwest part of the metro area lies under a “slight” chance of severe weather (damaging winds, hail and possibly a tornado) on Friday and Friday night.

Severe weather outlook for Friday. (NOAA)
Severe weather outlook for Friday. (NOAA)

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