Good morning to you after a fine Memorial Day weekend, when we rememberd those who died serving our country. We are all indebted to all of them. Today I’m going to take a final look at last week’s flooding, and what lies ahead.
FLOODS
As Braniff explained this weekend, Houston saw two days of large mesoscale convective systems (MCS) that were driven by backbuilding storms. On Thursday the heaviest rains were concentrated over the Brenham area, and on Friday the region saw more widespread rainfall. Here’s a false-color satellite view of the hard-hit northwest part of the Houston metro region on Saturday afternoon that shows the dramatic swelling of the Brazos River, and flooded watersheds between Katy and Hockley. Click the image to enlarge.
Annotated landsat image from Saturday afternoon. (CIMSS)
Most of the Houston area has remained shower-free this morning, but we’re becoming concerned about a boundary between warmer (to the south) and cooler air masses that has set up a bit to the north of Interstate 10 today. Its position at 11:45am CT is shown below.
Approximate position of boundary at 11:45am CT. (Intellicast)
We’ve seen storms form north of this boundary today, including over already hard-hit areas of southwestern Montgomery County, and this should continue. That’s because there’s an ample flow of moisture and warmth coming from the south-southwest which is helping to feed storm development. As the day progresses we could see this boundary sag further south, bringing some heavier storms into the central Houston metropolitan area.
There is a lot of uncertainty in the forecast, but even a few more inches of rain across northern Harris, southern Montgomery, Waller and Grimes county would prove very troubling. And the prospect of heavier rains moving southward into the central Harris County area later this afternoon to start off the Memorial Day weekend isn’t particularly appealing either. We’ll be keeping a close eye on developments for you.
We’re nearing the end of an incredible rain event over the northwest and northern Houston metro area. A final line of major storms moved through the northern half of the metro area this morning, a little before sunrise, and now it seems like the organized activity is finally ramping down. Here’s a look at rainfall totals between 5am CT Thursday, and 5am CT Friday:
Just an incredible evening of heavy rain north and northwest of the city of Houston, with 6 to 8 inches of rain falling across much of western Montgomery County, and 8 to 14 inches coming down over an area from Brenham to Montgomery. Many roads are impassable, including some locations of Highway 290 northwest of Harris County.
The National Weather Service has issued a Flash Flood Emergency for Washington and northern Austin Counties tonight due to extremely heavy rains in those areas. This is the highest level of flood warning. Multiple high water rescues have occurred in these areas.
Satellite estimates of rainfall between 10am and 10pm CT on Thursday. (NOAA)
Unfortunately storms are continuing to develop along a west-to-east boundary north of Interstate 10 tonight, and I think we’ll see continued development of storms for the next few hours. A flash flood warning is in effect for pretty much all of the northern half of the Houston metro area until at least 2:45am CT. Some homes along Spring Creek, in southern Montgomery and northern Harris County, have already flooded as the creek has risen several feet out of its banks.
The forecast is far from clear, but I think we’ll see additional storms move in from west during the overnight hours, with more widespread showers moving into the central and southern Houston metro area by, or around sunrise on Friday morning. I’m hopeful the heaviest rains will exist the region by mid-morning, or noon at the latest, but the entire Houston metro is under a flash flood watch through at least 7pm CT on Friday.
