What to know about spring floods

Spencer Highway and Beltway 8 last May 15
Spencer Highway and Beltway 8 last May 15

The cover picture above isn’t a throwback to Imelda or Harvey or Beta, nor is it a pic of the Memorial Day floods or Tax Day floods. That was May 15 and is a perfect example of the kind of flooding downpours we can get around here. Most locations on this day had zero rain to less than an inch, while Sugar Land reported 1.64 inches and Hobby 1.25 inches. But League City had 5.69 inches of rain and you can see what happened in Pasadena. Street flooding can come fast and furious around here.

Such street flooding is particularly dangerous -- just 6 inches of fast-moving water can lift a pickup truck! TxDOT is quick to remind us: Flash floods are the leading cause of weather-related deaths in Texas, and about 60% of flood-related deaths in our state involve motor vehicles.

In a recent press release, I think TxDOT buried the lead: the last time we had a single day in Texas WITHOUT a road fatality was Nov. 7, 2000! More than two decades ago. While not heeding road barriers or messing with them can get you steep fines, the ultimate price is one you don’t want to pay. So remember: Turn Around, Don’t Drown!

Spring flooding outlook

No one can accurately tell you if we might or might not get a sudden flash flood from thunderstorm downpours. But the National Weather Service can at least look at parameters regarding river flooding and soil moisture to determine what we are up against for major, widespread floods.

Katie Landry-Guyton, senior service hydrologist for the Houston NWS, recently published such a determination taking into account different parameters. Here’s my quick and easy take on her report:

How much has it rained the past three months? Below normal west/slightly above normal central and east.

How wet is the soil? About average.

How full and fast are the rivers? Streamflow is slightly above normal.

How full are the lakes and reservoirs? Mostly 100%.

What is our drought status? Normal to just a bit dry.

US Drought Monitor shows only Abnormally Dry conditions in SE Texas

And, finally, La Niña is still hanging around bringing a predicted below-normal rainfall the next 30 and 90 days:

90 Day Precip Outlook calls for BELOW normal rainfall

So what’s this all mean?

Put simply, we’re at a pretty equal chance for river flooding either way. You can read the full 2021 Spring Flood Outlook report at the top of the NWS home page. Here’s the report’s bottom line:

“Considering the pre-existing conditions and the rainfall expected for the next 90 days, the NWS anticipates a near normal chance of flooding this spring along the Trinity, San Jacinto, Brazos, and San Bernard River Basins, and a below normal chance of flooding along the Colorado and Lavaca/Navidad River Basins.”

And let me emphasize, again, none of this has anything to do with whether a sudden cluster or line of thunderstorms moving through produces flash flooding on our roads. They can and they do. It’s just a matter of time as to when we see that again. If it’s a help, models look pretty quiet for significant weather the next two weeks. But spring just started!

Frank

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About the Author:

KPRC 2's chief meteorologist with three decades of experience forecasting Houston's weather.