Heavy rains, multiple flood warnings … and it’s just Tuesday

Earlier, we posted that we expected the heavy rainfall to wane between 6pm and 9pm this evening. Unfortunately, the storms have sustained themselves as the sun has gone down and continued to pile on rain totals—especially to the southwest of Houston in areas such as Sugar Land and Richmond. Regions there have now recorded 8 to 10 inches, nearing the exceptional amounts recorded in Humble and Kingwood earlier today and this afternoon.

Tuesday rain totals were very impressive NE and SW of Houston. (HCOEM)

So what happens now? With the sun now falling below the horizon, the rain cooled atmosphere will have less energy to sustain itself, and from a pure physics point of view, these heavy rain showers really should really ebb over the next 3 to 6 hours. But it is hard to have overly much confidence in this forecast given how much we’ve missed already today. We’re hoping for a break later tonight and perhaps Wednesday morning.

Where does this leave us? Quite frankly, we didn’t anticipate that the rains would be as intense as they were today. Certainly, we didn’t expect 10 inches of rain for any part of metro Houston, nor the need for high water rescues as are presently ongoing in southwest Houston. Yet here we are on the first day of a multi-day event, with soils now thoroughly sodden; some bayous near bank full; river concerns; and more.

Forced to guess, I’d say we’ve got two more major rounds of storms to worry about after this evening. There likely will be widespread showers on Wednesday night and Thursday, and then some kind of mess on Friday and Saturday. If those rounds are as bad as we’ve had today, then we’re going to see a much worse situation than now, but I don’t think we can quite say that yet.

We’ll be back with a full report in the morning.

Day one of heavy rainfall in Houston is unfortunately delivering

It’s been a day in Houston, with some very heavy rainfall across parts of the city. If you live in Kingwood, congratulations, so far you’re the big winner with about 6+ inches of rain. With lots of street flooding in the area, it’s a mess trying to get home this evening along I-59 north, as well as I-59 south toward Sugar Land.

Houston radar at 4:20pm CT is covered by slow-moving showers. (kktv.com)

Most of the high-resolution model forecasts indicate that the current widespread activity should die down this evening, by 6 to 9 pm, which should coincide with the loss of daytime heating. From that point on, we will hopefully see a reprieve from heavy rainfall during the overnight hours.

Wednesday is a bit of a crapshoot. There is a scenario, which I’d probably lean toward, that keeps most of the heavy rain away from Houston as a cold front remains north of the metro region—including away from Kingwood and surrounding areas hard hit on Tuesday. But frankly, given the intensity and widespread nature of the storms Tuesday I don’t have great confidence in the forecast for Wednesday. Hopefully the forecast is a bit more clear in the morning.

From now through Saturday it’s going to be a day-to-day thing.

Storms, heavy rain, coming to Houston over the next five days

The radar is mostly quiet this morning across the region, but that will soon change with the onset of showers and thunderstorms later today. From there on we will enter a very wet, and somewhat unpredictable period, during which rainfall should peak from Thursday evening through Saturday. Below, we do our best to assess this mess, and use our new flood scale for the first time.

Tuesday

Generally, we expect rain showers and thunderstorms to develop south and west of Houston this morning, and then migrate north of I-10 later today. But admittedly, that is just a guess. The high-resolution models we use to predict the development of these small-scale storm systems have been failing us of late, so we don’t have great confidence in these storms. Accumulations of 0.5 to 1.5 inches are possible for some areas today, while parts of the region are likely to see no rainfall at all. Highs will only reach about 80 degrees. Lighter rain will be possible Tuesday night, but most of the region should see a break.

Severe Weather Outlook for Wednesday. (NOAA)

Wednesday

The weather story for Wednesday will be the propagation of an upper-level system across northern Texas, which will drive the potential for severe weather over parts of Texas, including Austin, and East Texas (see map above). It remains to be seen how close these storms come to the Houston metro area, but Waller, Walker, and Montgomery counties could well see damaging winds and hail in addition to 1 to 2 inches of rainfall. Southern parts of the Houston region may not see too much rain Wednesday.

See full post

Introducing the Space City Weather Flood Scale

Ever since Hurricane Harvey, a lot of people living in and around Houston become nervous at the mention of widespread, heavy rainfall. The mere suggestion of even minor flooding heightens tension. And after surviving Harvey, we certainly understand why.

In the months after Harvey, Matt and I got together to try and determine what, if anything, we could do to help ameliorate this situation. Eventually, Matt hit upon the idea of a “flood scale” that residents of the greater Houston area could use to calibrate their concerns about upcoming flood events. Over time, the scale evolved into a rating from Flood Stage 1 (street flooding) through Flood Stage 5 (Hurricane Harvey). Here’s what we came up with:

Space City Weather Flood Scale.

This scale is not officially sanctioned by any government organization. Nor are we seeking to usurp any authority from the National Weather Service—they command our highest respect in issuing flood watches and warnings. Rather, we felt there was a need for something like this, in advance of significant weather, to help our readers set expectations and manage their own anxieties. So we’re providing the scale as such a service. It remains a work in progress.

In truth, there are many, many ingredients that will determine the impact of a flood: the total amount of rain, intensity of hourly rainfall rates, how long the rains last, the preexisting saturation of soils, the time of year, and more. This scale attempts to incorporate all of those factors into the ranking the impact of a flooding event. It is not perfect, nor purely quantifiable, but is does represent our best attempt to determine what residents can expect.

So why are we introducing this scale now? Because we anticipate needing it for the coming Thursday through Saturday period. Absent a major change in the forecast models, we’ll begin to use the flood scale beginning in Tuesday morning’s post. For what its worth, our overall thinking hasn’t changed, we continue to see the potential for 3 to 10 inches of rain through Sunday morning for the Houston region.