Eric Berger

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.

Yeah, we have concerns about heavy rainfall this week

After a stunning Sunday, the sunshine is mostly going to disappear for some time, and Houston faces a significantly wetter period in which we may have some flooding concerns. There is, frankly, not much confidence in any of the forecast models at this point, but all point to a period of on-and-off heavy rainfall due to a moist atmosphere and meandering fronts.

NOAA seven day rainfall forecast for Texas, through next Sunday. (Pivotal Weather)

The bottom line is that the region could see from 4 to 10 inches of rain—roughly speaking—over the next seven days, but it’s hard to pin down the best days and locations for accumulations at this time. On a day-to-day basis we may have concerns about street flooding. We also have concerns about the Trinity (which already will near major flood stage Wednesday near Liberty) and Brazos (already forecast to reach a minor flood stage Friday morning at Richmond) rivers, as these rains could add multiple inches of rains to those basis. Then, as the week wears on, our grounds may become increasingly saturated and vulnerable to heavy rainfall events that move past street flooding and into yards. Overall, this will be a week to pay attention to forecasts, and we’ll do our best to stay on top of what appears to be a dynamic situation. Please clap—I resisted saying it was a fluid situation.

Monday

We can have the most confidence in our weather for Monday. We’ll see a mix of sunshine and clouds today, and the additional sky cover should help to limit temperatures in the mid-80s. This is probably the last day, for a week or so, that we can definitively say it will not rain. Also, after drier air filtered into the region this weekend, an onshore flow today will begin to pump moisture back into Houston, setting the stage for wetter days ahead. Lows Monday night will fall into the lower 70s for most.

Tuesday

On Tuesday, a disturbance in the mid-levels of the atmosphere will bring a healthy chance of rainfall into the region, with most of the rains likely falling during the daytime hours. Rain accumulations across Houston will probably range from 0.25 to 2.0 inches, although some areas will undoubtedly see less, and some more. Our biggest concern is that some areas will see heavy rainfall during this time as the overall dynamics do not favor severe storms, for the most part.

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Heavy rains end for now, so enjoy your weekend Houston

A major line of storms pulsed through the Houston area early Saturday—but well before sunrise they pushed to the east of the region. Some lingering showers are possible later this morning, but for the most part we should be dry from here on out. The overnight storms dropped 1-2 inches of rain, and may have spawned a tornado.

Now, however, we should see a nice May weekend. Clouds should eventually break apart this afternoon, leading to a pleasant evening, with inland parts of the region potentially seeing lows in the upper 60s. Sunday should see mostly sunny skies, with highs in the upper 80s to 90 degrees.

The end of next week does look wet. (Pivotal Weather)

As Matt mentioned Friday, the coming week looks potentially quite wet, especially the period from Thursday through Saturday. It’s too early to have too much confidence in the timing and details, but a slow-moving front could make for very wet conditions, with multiple inches of rain and the potential for at least some street flooding. But we wouldn’t worry too much about that yet; for now enjoy the weekend and we’ll provide a full (and hopefully clearer) update of the situation on Monday morning.

After a wet, maybe stormy couple of days, a decent weekend awaits

Houston faces a couple of wetter, and potentially stormy days before our weather clears out sometime on Saturday, and brings us what looks like a fairly nice May weekend. But first we’ve got to get through a round of storms this morning, for the northern half of the region, and then a stormy period on Friday night. We’re not anticipating anything too severe, but we could see some at-times strong thunderstorms.

Houston radar at 6:30am CT. (kktv.com)

Thursday

As of 6:15am CT, the northern part of Houston is seeing the remnant line of showers and thunderstorms from a large storm system that moved through North Texas on Wednesday night. This line is slowly weakening as it moves to the south-southeast this morning, but some part of it will likely push through The Woodlands and down at least into central Houston. Closer to the coast, a capping inversion will likely prevent widespread showers and thunderstorms. After this system works through this morning, we can expect a partly sunny day with highs in the mid-to upper-80s.

The storm outlook for Friday and Friday night is somewhat supportive of severe weather. (NOAA)

Friday through Saturday morning

We’ll see another wetter period on Friday through Saturday morning for the region. Most of the action should remain to the west and north of the Houston metro area through the daytime hours on Friday, but sometime that evening we should see a mass of storms move through the area roughly from west to east. This system is part of a weak cold front and an upper level disturbance. Timing is still hazy, but generally we’d expect the worst weather overnight for most of Houston, and probably lingering into Saturday morning for the coast and eastern parts of the region. Most modeling shows the system clearing the area by or before noon on Saturday, but we’re offering no guarantees. Generally, the area will probably see 0.5 to 1.5 inches of rain, but there may be higher localized totals, and we can’t rule out some hail and damaging winds.

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