Just a quick midnight update on the state-of-play with Houston’s storms…

A heavy round of showers has now pushed east of the metro region, moving along the coast and toward Beaumont. Behind that, the front (with much lower dewpoints) is pushing into southeast Houston. And behind the front, there’s another area of fairly heavy storms moving east-northeast. We think this is probably the last really burst-y area of storms that will affect Houston tonight. After this, from 2am or 3am onward, we should see some additional light to moderate rainfall, but this too should peter out by around sunrise or shortly thereafter.

We’re still concerned about the West Fork of the San Jacinto River, which we mentioned earlier, and South Mayde Creek and Langham Creek in Western Harris County are out of their banks and spilling into nearby streets and parks, according to the Harris County Flood Control District. Elsewhere, bayous and creeks are holding.

This is almost over, so hang tight, and lets begin to dry out come sunrise.

Good evening. We’re continuing to monitor conditions across the metro area and rainfall totals remain manageable for most of the region. We have two main concerns: flooding along the West Fork of the San Jacinto River, and the potential for more heavy rainfall later tonight as a main line of at least semi-organized storms moves through. Overall, most of Houston will come through this just fine, we believe.

San Jacinto River

The West Fork of the San Jacinto River, which is downstream of some of the heaviest rainfall today, may potentially go into major flood stage on Saturday or Sunday. According to the Harris County Flood Control District, the following subdivisions may see impacts: Forest Cove, Rivercrest, Northshore, Belleau Woods. Kingwood and Atascocita appear unlikely to be affected at this time.

Main line of storms

So far today, rainfall amounts for most of the metro area have remained near 2 inches or less (we’ve seen more than this up north, in some parts of Montgomery County and elsewhere). These are quite manageable for area bayous.

As of 8:45pm CT we are seeing storms get organized just west and north of Houston, and from now until about 3am CT we are likely to see the potential for additional heavy rainfall as this mass of storms moves through, from west to east along with the front. Conditions will likely deteriorate for much of Houston over the next hour or two, so now is the time to be wrapping up any activities and getting home.

Most areas may see an additional 1 to 3 inches of rainfall from now through 3am—which should be fine for most bayous—although a few areas may see a bit more than this. After 3am we should see a slackening in rainfall on the west side of the metro area, and then a gradual ending beginning shortly before sunrise from west to east.

Saturday will be gray, and chilly, with highs in the 50s and blustery northerly winds.

We will update later tonight if warranted.

Rains so far today have stayed mostly to the north and west of the Houston metro area, as anticipated. As of 2pm CT, just south of Huntsville is the big “winner” with about 4 inches of rain falling so far. Not a whole lot has changed with our forecast, but I did want to call out a few things we’re watching as we get closer to heavier rainfall this evening and during the overnight hours.

Models not showing extreme totals: None of the high-resolution models are really bombing out huge rain totals with this event. So while some forecasts have been calling for up to 10 inches of rainfall during the next 12 to 24 hours. We’re feeling more comfortable with 7 or 8 inches as an upper limit, with most of the area seeing 2 to 5 inches of rainfall.

Heavier rains more likely north: Some of the models suggest the heavier rain totals (5 inches or more) will generally fall north of Harris County, with most of the metro area remaining under that threshold. Other models show the rainfall pretty well dispersed, so we’re not overly confident with this part of the forecast.

Line of storms timing: The point at which the front (and a line of strong thunderstorms) moves through Houston has moved up somewhat, and now appears likely to sweep through the region, from west to east, between around midnight and 3am. This is the time when you definitely won’t want to be out and about due to the potential for heavy rainfall, flooded streets, and strong thunderstorms.

Flooding potential: Because some of the heaviest rainfall will occur well inland, we’ll have to watch for potential flooding along the Trinity, San Jacinto, Brazos, Navasota, San Bernard, and Colorado river basins. In terms of bayous, Jeff Lindner of Harris County said he’s most concerned about bayous and creeks across the northern, northwestern, and northeastern parts of the county: Cypress, Willow, Little Cypress, Cedar, West and East Forks of the San Jacinto, South Mayde, Langham, Bear. We think most of these will probably remain within their banks.

Event will end: We are not overly concerned about Friday night’s event, because it’s going to come to a pretty abrupt end by or before sunrise on Saturday. This will be kind of a nasty rain event for December, but if this were July or August, it wouldn’t be considered all that extreme. Our bottom line is that, if you’re overly anxious about this event, it’s probably not going to be as bad as you think.

We’ll be back this evening with an updated forecast.

Good morning. Let’s get right into the forecast here, as a significant winter rainstorm begins to bear down on Southeast Texas.

First off, Flash Flood Watches will go into effect for the entire region today and tonight.

This means conditions will be favorable for flash flooding, street flooding, and some substantial rises in area creeks, rivers, and bayous. If you’ll be out and about tonight, you will want to have a way to receive updated weather information. Space City Weather will be updated through the night as well, but make sure you have a couple sources of the latest information and a way to see radar.

Also, something that’s occasionally underappreciated: If possible, please make sure your neighborhood storm drains are free of leaves and debris. We are “past peak” fall foliage in Houston now, and many leaves have found their way to storm drains and gutters.

Reminder: before the rain, please clear your drain!#ThursdayThoughts #weatheraware
You can adopt your drain at https://t.co/V9XMMXl3yZ pic.twitter.com/Z3hVsqsETv

— Houston Public Works (@HouPublicWorks) December 6, 2018

Clearing these areas allows water to drain more effectively and will often mitigate some street flooding issues.

This morning

Radar this morning is quiet in Houston, but scattered showers have developed northwest of the city.

Expect scattered showers and the possibility of some thunder to continue through the morning hours north and west of Houston. This area should advance closer to Houston as well, bringing some rain chance to the city by late morning.

This afternoon

Expect showers and thunderstorms to become more numerous and widespread as we go through the afternoon, especially along and northwest of US-59. We will want to watch this to see if rain can advance farther southeast than expected, as this could push the steadier rains more into the central part of the Houston metro, rather than it being skewed northwest. Regardless, I don’t anticipate that we’re going to see a lot of flooding issues around the region through afternoon. That risk ramps up tonight (read more below).

But still, I would expect that we could see on the order of a half inch to two inches of rain on average during the daytime today from the city of Houston to the north and west, with lesser amounts south and east. However, we will need to watch southern and eastern areas later this afternoon for some isolated potentially strong to severe storms.

This evening

Steady rain could taper to scattered showers in spots, but in general, expect occasional showers, downpours, and thunderstorms through midnight, with the greatest concentration from the city of Houston to the northwest.

The image above is a forecast radar for 9 PM this evening. You get a sense of the patchy nature of things. Not everyone will be in downpours constantly, but some areas will get hit more often than others. If you get into a lull in the rain, just be advised that the event isn’t over and heavier rain will be incoming overnight from the west.

Overnight

This will be the main event. A strong, slow moving line of thunderstorms will plow across the entire region around or after midnight. This band of storms will be capable of producing 1-3″ of additional rain, or more, in short order as it moves west to east across the area. After today’s rains, grounds will be saturated, and runoff will be quicker than usual. This will be the band of rain most capable of producing widespread street flooding and leading to rises on bayous in the area. The areas most vulnerable to flooding will be those that see the most rain during the day today and in the early evening. Our assumption is that we’ll see this occur along and northwest of US-59. But we will obviously know more this afternoon as this event begins to setup.

Once all is said and done, we expect two to five inches of rainfall across the area, with a few locations perhaps seeing as much as five to ten inches of rain. That will not be the case in most of the area, but there will be dollops of some of those bigger ticket totals in parts of the region. As noted, where those occur will determine who exactly is at highest risk of flooding. Obviously, use extreme caution if you’ll be travelling tonight and never drive through flooded roadways, especially at night, when it’s extremely difficult to judge how deep that water is that’s covering the road. Eric will have an update on how things are progressing later today.

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