Those who have stepped outside today are well aware that we’re currently experiencing an early preview of winter temperatures. It is cold, dreary, and for some, quite wet. Yet the cold front that has now pushed through much of Texas is fairly shallow. Above the colder air in the low-levels of the atmosphere is a more moist airmass. With overhead lift thanks to a storm system sitting in the Southwest United States that moisture is what is causing the widespread rains today. That will not change tonight or most of Tuesday, but we’ll see a general decrease in coverage by Tuesday night.
Rainfall rates have not been excessive today so flash flooding has not been a widespread occurrence. Flash flooding has not been a problem, but flooding is occurring. We’ve seen rather significant rises on several watersheds across North Texas with Joe Pool Lake being one example. It is now approaching eight feet above normal. Several others lakes are feet above their normal pool as well. Soils are near complete saturation due to rains over the last several weeks. Any rain that falls will simply runoff into tributaries, rivers, and watersheds. That process will result in more rises and the potential for more flooding. Flash flooding will be possible tonight into Tuesday in locations that do end up receiving higher rain totals in a short period of time. Keep in mind that the threshold that would typically produce flooding is lower since everything is saturated. While water rises may be more steady versus rapid, we are anticipating roadway closures due to flooding – just in a slower fashion than if you had five inches of rainfall in 90 minutes.
The National Weather Service/Weather Prediction Center has the highest corridor of rain through Tuesday across the Concho Valley, southern North Texas, extending into East Texas. While the graphic’s rain totals are through Wednesday, most of this is expected to fall tonight through Tuesday evening. Widespread additional rain total of two to four inches is expected in that corridor. Localized rain totals may exceed five to six inches. Localized amounts will vary, some will see less and some could see more than the graphic shows. This rain event will be longer duration with those rain totals spread out over the next twenty-four to thirty-six hours. That’ll reduce the threat of rapid water rises, but will still cause steadily rising water and flooding. Soils are simply too saturated across parts of Texas to handle any more rain. Any rains that fall now will simply run-off into tributaries, rivers, and watersheds. Flooded roadways and your typical low-water crossings will still have flooding issues, but waters will likely rise more steadily versus rapidly. This kind of flooding is plenty dangerous and if you drive a vehicle into flood waters they’ll still total your vehicle.
This model-simulated weather radar runs from late tonight through Wednesday morning. It shows the upcoming scenario pretty well. We’re anticipating a fairly wide corridor of rain in a longer-duration event. Hourly rain totals will stay below one inch for most locations, but with many hours of upcoming rain, the rain totals will still add up. Any rain totals that exceed an inch per hour raise the probability of more rapid water-rises and flash flooding. Otherwise, we’ll still see a threat of flooding, but water rises will be more steady.
The general expectation is that rainfall will decrease in coverage and intensity Tuesday night as upper-level forcing begins to decrease. Lighter rains will continue into Wednesday. Lighter rains Tuesday night and on Wednesday will likely not cause any additional flooding (excluding predicted river/watershed rises), but this light rain will slow/complicate relief from any ongoing flooding. Confidence is beginning to increase that another rain event with multi-inch rain totals could impact portions of Texas beginning Thursday through Friday. Some may see a drying trend on Saturday and Sunday, but I hesitate to promote that notion given our recent trend of washing out all weekends.