National Weather Service forecasters said a strong upper level low pressure system will merge with a surface cool front tonight in North Texas.
But the region is already stoked with "moisture-rich" air from the Gulf of Mexico, courtesy of strong southerly winds that will continue throughout the day, the agency's forecasters said.
Those factors are expected to produce widespread heavy rainfall, the forecasters said.
"The main threat of heavy rainfall and flash flood potential will be from Monday evening through early Wednesday morning," the forecasters said in their flash flood advisory.
NWS radar shows all these factors in play. Click here to see more.
-- Bill Miller