Flash Flood Watches Issued as Texas, Neighboring States Brace for Extremely Heavy Rain (FORECAST)

Jon Erdman
Published: October 21,2015

More than 10 million people are under flash flood watches as a potent but slow-moving storm system begins to team up with moisture-laden air from the Gulf of Mexico, setting up the potential for extremely heavy rainfall across a large part of Texas and neighboring states over the next few days. Moisture and energy from Tropical Storm Patricia in the eastern Pacific may also add more fuel to this soaking scenario.
For the second time this year, excessive rainfall is forecast for areas of Texas where drought conditions have worsened in recent months. A series of heavy rainfalls in May dumped more than 20 inches of rain on parts of the state, virtually wiping out a long-term drought and causing destructive flash floods. Since then, the state has snapped back into drought, setting the stage for wildfires over the past few weeks.
(MORE: Drought Returns Again | May Floods Leave Death, Destruction)
Here are the details on the heavy rain threat and how the tropics may be involved.

Heavy Rain, Flood Threat in the Southern Plains

Persistent southeasterly winds are pumping moisture from the Gulf of Mexico into the southern High Plains, where it will interact with an area of low pressure aloft over the Southwest. This will contribute to heavy rains as far west as eastern New Mexico, western Texas, western Oklahoma and southwest Kansas through Thursday morning.
Flash flood watches have been issued by the National Weather Service for much of Texas, including the Dallas-Fort Worth metroplex, eastern New Mexico and central to western Oklahoma.

Flood Alerts

This rain will spread across the rest of Texas, Oklahoma and possibly parts of northwest Louisiana and Arkansas by Thursday night or Friday. A separate weather disturbance moving through the southern tier of the U.S. will prolong the heavy rain threat into this weekend across those states.

Forecast Next 5 Days

In addition, moisture and energy from Tropical Storm Patricia in the eastern Pacific could be involved in this setup by this weekend. Computer forecast models are showing that after it makes landfall in Mexico, the mid-level remnants will get pulled northeastward into the south-central states by a southward dip in the jet stream over the western and central United States.
(MORE: Tropical Storm Patricia Forecast to Strengthen)
In all of the above mentioned areas, flash flooding is possible where heavy rain persists the longest. However, small-scale details will dictate exactly where this threat will be the greatest in the coming days. Our rainfall forecast map shows that a widespread area of the southern Plains has the potential to see 3 or more inches of rain through this weekend. Some areas may pick up 10 inches or more of total rainfall.

Rainfall Outlook

In addition, persistent onshore winds will bring some minor coastal flooding, high surf and dangerous rip currents this week to the Texas and Louisiana coasts.
Coastal flood advisories have been issued for portions of the Texas and Louisiana coasts.
(FORECASTS: S. Padre Island | Corpus Christi | Houston | Lake Charles, Louisiana)
This rain is needed to help a relatively rapidly-developing flash drought, which set in over the southern Plains and Lower Mississippi Valley from mid-summer on.
The heavy rain threat, while squelching the recent wildfires, may be too much of a good thing in these areas, instead triggering flash flooding.
(MORE: Expert Analysis | Hurricane Central)

Timing the Flood Threat

Thursday:

• Main Threat Areas: much of texas Texas, western Oklahoma, and western Kansas. Rain advances east into central portions of Oklahoma and Texas into Thursday night.
• Cities: Amarillo | Lubbock | Midland | Dallas-Fort Worth | Oklahoma City

Thursday's Forecast

Friday:

• Main Threat Areas: eastern Oklahoma, northwestern Arkansas and northern to central Texas.
• Cities: Dallas-Fort Worth | Fort Smith, Arkansas | Oklahoma City | San Antonio

Friday's Forecast

Saturday:

• Main Threat Areas: central and eastern Texas, southeastern Oklahoma, Arkansas and possibly western Louisiana
• Cities: Austin | Dallas-Fort Worth | Houston | Little Rock

Saturday's Forecast

PHOTOS: May 2015 Southern Plains Flooding