It has been a week since catastrophic flooding in Texas Hill Country. At the time of writing the death toll exceeded 120 people with roughly 170 missing. As the tragedy unfolds, important questions are being raised about the lack of a real-time warning system, why certain infrastructure is located in a known floodplain, and barriers with dissemination of available weather warnings. If this was a plane crash, the National Transportation Safety Board would investigate what happened. There is no such function for weather disasters, though many colleagues have called for this capability over the years. In light of that void, here is a breakdown of five key meteorological ingredients that contributed to the Texas floods.
As I wrote last weekend, NOAA’s Weather Prediction Center pointed to the possibility of a heavy rain event in that area as early as June 30, 2025. That’s four or so days in advance of the event. In that Day 3 to 7 U.S. Weather Hazards Outlook (map above), a heavy rain region in western Texas is predicted for July 3, 2025. It is clear to me that NWS forecasters sniffed out this potential well in advance of the disaster.
I teach a course at the University of Georgia called Mesoscale and Radar Meteorology. In that class, one of the most important units focuses on identifying and forecasting extreme rainfall events. In 2011, my colleagues and I published a paper identifying meteorological factors that led to the Atlanta Floods of 2009. Like the Texas flooding, that event was caused by an “unfortunate perfect storm” of ingredients.
Moisture
Moisture is one of the most important ingredients, and there was a lot of it. The National Weather Service wrote on July 2, 2025, “A substantial plume of deep tropical moisture continues to stream north across South-Central Texas, characterized by unseasonably moist precipitable water values as high as about 2.4 inches.” Precipitable water is a tool that meteorologists use to indicate how deep the reservoir of moisture is in the atmosphere. Studies have shown that extremely high values of PWAT are a key indicator of flood potential. Forecasters saw this possibility in Texas in the days preceding the tragedy. Satellite estimates (shown in the map above) show plumes of moisture streaming northerward into Texas even in the days after July 4.
There were other sources of moisture too. The remnants of Tropical Storm Barry, the second named storm of the Atlantic season, was a moisture source after it made landfall in Mexico. Additionally, a weakening former Hurricane Flossie in the eastern Pacific basin may have also provided moisture as Weather Channel meteorologist Jen Carfagno pointed out on a recent episode of the Weather Geeks podcast. All of these factors produced record moisture levels in the region.
Rising Motion and Convergence
Other key ingredients needed for extreme rainfall are rising motion and a focusing mechanism to get the air to go up. The NWS discussion on the day before the rainfall noted, “The axis of a negatively tilted mid-level trough most readily apparent on 700mb analyses is beginning to move poleward towards the Edwards Plateau, leading to rounds of shower activity throughout South-Central Texas into tomorrow as the advancing trough prompts the ascent of moist air.” There was also a spinning feature known as a mesoscale convective vortex that also contributed to both of those ingredients. The MCV is a dynamic rotating feature that can enhance rainfall and storm genesis. The Precipitation Systems Research Group at Colorado State University discusses MCVs on their website. They pointed out, “The latent heating in a large complex of deep moist convection will often produce a cyclonic vortex at midlevels—generally known as a mesoscale convective vortex (MCV). If the conditions are right, these vortices can then go on to initiate additional convection.”
The Texas Hill Country mainly impacted runoff once the rain fell to the surface. However, when ever I see any type of elevated terrain, my meteorological instincts known that any “orographic” boost by hills or mountains must be considered too. The mountains were likely a factor in the enhancement of lift during Hurricane Helene, for example.
Slow Movement
Another factor in flooding events was speed (or lack thereof) of the storm system. This particular system was slow-moving. In fact, flood warnings remained for the region in the days after the initial tragic rainfall event. Whenever a system of any type stalls in an area or is very slow to move, a rainfall disaster is likely. Harvey (2017) sat over southeastern Texas for days. Hurricane Florence (2018) and its remnants lingered and caused significant flooding throughout the Carolinas. A cutoff low sat to the west of Georgia for days pumping moisture into Atlanta during the 2009 floods. Over 200 people died in the Spanish Floods of 2024. A cutoff low was a major factor.
Warm Gulf Waters
Another aspect of this event that may be overlook is the warm Gulf waters. They had a direct impact on the brief development of Tropical Storm Barry. However, I want to identify a secondary impact. Warm Gulf waters also enhance the moisture source for the atmosphere because they tend to be associated with higher evaporation rates. Evaporation is a mechanism for transferring moisture from the water to the atmosphere.
Rainfall Intensity
In general, the duration of the rainfall and how fast it is falling determines how bad flooding will be. In this storm, particularly during the initial event, rainfall rates at times were 2 to 4 inches per hour. That’s a lot of rain falling over a short period of time. Now couple that with all of the complex terrain and relatively stalled system. For context, massive flooding in New York City was caused by the remnants of Hurricane Ida (2021). Over 3 inches of rain fell in an hour over Central Park.
My doctoral studies at Florida State University investigated how efficiently sea breeze and outflow boundary storms convert atmospheric moisture to precipitation. Mid-level moisture and depth of convergence were critical factors in the precipitation efficiency of those types of storm. Unfortunately, the Texas storms had sustained, deep moisture being lifted into the system.
Though there has been a lot of chatter and conflation, cloud seeding was likely not a significant or even minimal factor for the reasons discussed in my previous article. University of Texas El Paso professor Tom Gill stated it perfectly, “Cloud seeding is like a match. Trying to light a rock with it (no water vapor) is useless. And lighting a match on a blazing inferno (very moist atmosphere, like on July 4th morning over Texas Hill Country) also won’t have any noticeable effect.”