Heavy rain, flooding possible Friday night
A slow moving cold front is expected to bring heavy rain and thunderstorms to most of the CBS Austin viewing area beginning Friday evening through Saturday morning. Many locations have already seen 5+ inches of rain this month which has saturated the soil, and with more rain on the way, flash flooding will be possible mainly west of I-35 Friday night and Saturday morning. Here is how this event will play out.
First, the National Weather Service has issued a FLASH FLOOD WATCH until 7 AM Saturday for Mason county, and until 1 PM for the rest of the Hill Country along and west of Highway 281. This means that conditions are favorable for excess rainfall that could result in flash flooding.
The "cold" front is expected to move into the Hill Country Friday night, moving slowly from west to east over the following 12 hours or so. Heavy rain and thunderstorms are expected to develop along and ahead of that front, and with the atmosphere holding back a lot of moisture, the rain could be torrential at times; 1-3" per hour rainfall rates will be possible. Here is a snapshot from one of our computer models around 10 PM Friday night:
This line of showers and thunderstorms will be most robust in the Hill Country into very early Saturday morning, but could weaken and potentially fall apart as it moves closer to I-35 by sunrise. This is almost entirely due to the timing of this front... Overnight/morning rain is generally less intense than rain that would fall in the afternoon thanks to cooler temperatures, which limits the amount of energy available for heavy rain and storms to tap into. That's why the highest threat for flash flooding will generally remain west of I-35. Here's the excessive rainfall outlook from the Weather Prediction Center that takes us through 7 AM Saturday morning.
A MODERATE or SLIGHT risk for excessive rainfall/flash flooding is in place West of Austin where 1-4" of rain could fall with isolated totals over 5" possible. Along I-35, the risk is certainly lower with only 1-3" expected, but the threat for flash flooding can't be ruled out. After Saturday morning, the threat for flash flooding area-wide is much lower with only scattered shower and thunderstorm activity expected mainly east of I-35 through Saturday evening. Here's a look at our forecast rainfall totals through Sunday:
BOTTOM LINE: Flash flooding will be possible along and west of I-35, with the highest threat between Friday evening and Saturday morning in the Hill Country. Flooding of low water crossings and poor drainage areas could occur. If you encounter a flooded roadway, don't risk it; turn around and find another route. The threat for heavy rain will be lower by Saturday afternoon with a lower flood concern through the end of the weekend.
THE GOOD NEWS: With this front pushing through the area, I expect activity to wind down for Saturday night plans. Have the rain gear handy if you're attending UT vs TCU at DKR Memorial, but odds are the show will go on without a hitch. Temperatures will be cooler behind the front as well with highs Saturday and Sunday near 80 degrees. Also, no severe weather is expected this weekend.
Make sure to download the CBS Austin Storm Tracker app on your phone to get the latest updates on flash flooding in your area. We'll bring you updates on air and online as needed through the weekend! Stay safe and have a great weekend.
-Meteorologist Avery Tomasco