Rain is about to mess with Texas in a big way. And though they may be football rivals, Oklahoma is also in for a wallop, as large portions of both states are under flash flood watches and warnings through Saturday.

A trifecta of factors are coming together that could dump nearly a foot of rain across the region in the next 96 hours. An upper low coming from the Southwest will get a double dose of tropical moisture from both the Gulf of Mexico and the Pacific. The latter will come courtesy of the remnants of Hurricane Patricia, which is expected to make landfall in Mexico late Friday night.

The beginnings of the heavy rain are already working across the Oklahoma’s Panhandle and West Texas. Totals ranging from 3 to 7 inches have already fallen there. But when all's said and done, east and central Texas could pick up the lion’s share of rain, with up to 11 inches possible. The state average for rain through this weekend is 3.6 inches, which would be roughly the equivalent of more than 17 trillion gallons of water falling on Texas.

Expected rainfall amounts across the U.S. from Oct. 22 to 27 2015

Expected rainfall amounts across the U.S. from Oct. 22 to 27 2015.

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Heavy downpours are on the rise across the U.S. Texas has seen an 8 percent increase in the number of heavy downpours  — defined as the top 1 percent of heaviest rainfall events — since 1950. This heavy rain come on the heels of a four-month string of very dry months for Texas and the Southern Plains at large.

“It has been an all-or-nothing year for the South Central U.S.,” Brad Rippey, a meteorologist with the U.S. Department of Agriculture, said.

Rippey wrote the text accompanying the weekly U.S. Drought Monitor update released on Thursday, a report that’s going to quickly be irrelevant. Texas and large parts of the Southern Plains have dealt with severe drought for as long as five years. After a late May and early June soaking, drought disappeared only to come back with a vengeance this summer.

“From southern Oklahoma and central and eastern Texas to the Mississippi Delta, the four-month period from mid-June to mid-October featured huge precipitation deficits that have caused all of the troubles that I wrote about in this week’s U.S. Drought Monitor text,” Rippey said. “But now, we have relief — but in the end it will be too much for some areas.”

A flash flood watch is in place for a 550-mile stretch from the Texas-Mexico border to metropolitan areas including Dallas and Oklahoma City through Saturday. Flash flood warnings are also in place in parts of central Texas through this afternoon.

The tropical roots of the rainfall may extend beyond Patricia. During El Niño years, the southern tier of the U.S. tends to be wetter than normal.