FORT WORTH -- Large hail, damaging winds and maybe even some tornadoes would result from severe weather that's expected to arrive around midnight in the Metroplex, according to the National Weather Service.
Several factors are developing that, if they match up, could produce severe weather similar to what North Texas saw on Monday when two tornadoes were spotted in Johnson County.
The main ingredient is an upper-level disturbance that was over Southern California at 8:30 a.m., said Nick Hampshire, meteorologist for the weather service's office in Fort Worth.
"But it's moving pretty fast," he said. "By 7 p.m. it should be in Western New Mexico, and a few hours later it should be close enough to us to get things going."
Included in the mix of ingredients is a cold front that was moving south from Kansas and Nebraska, destined for a late-night link up with the upper-level disturbance from California, Hampshire said.
Also, a dry line boundary was expected to stall west of the Metroplex, he added. The line separates dry desert air and the moist gulf air, but it triggers storm activity as it pushes east, mingling the dry with the moist.
And there was plenty of humidity in North Texas Thursday morning, courtesy of the Gulf of Mexico.
Damaging winds and large hail could result, along with tornadoes, although widespread outbreaks of funnel clouds aren't expected, Hampshire said.
The chances for rain were downgraded slightly overnight from 50 percent to 30 percent this afternoon, according to the weather service.
But this evening, the chances for rain accelerate as the ingredients for severe weather draw near to each other.
"It goes to 70 percent at 7 p.m.," Hampshire said, "and then to 80 percent after 1 a.m."
POSSIBILITY FOR RAIN
The National Weather Service officials attache a percentage to their rain predictions for precipitation, but the system they use involves a "12-hour probability of precipitation or POP12." This refers to the likelihood, expressed as a percent, of a measurable precipitation event (1/100th of an inch or more) during the 12-hour period in a particular area.
In our case that generally means Tarrant and Dallas Counties -- the Metroplex.
The POP, usually for rain or snow, can be illustrated by an example, so let's use tomorrow, which calls for 50 percent probability of rain in the Metroplex. This means that there's a five-in-10 chance that any location in the Metroplex will receive at least 1/100th of an inch of rain.