With another round of violent weather across parts of Texas and Oklahoma Thursday night (May 28), the death toll in the Southwest climbed to at least 27 after a Dallas truck driver was discovered inside his truck in a flooded Dallas culvert early Friday morning.

So far 23 deaths related to the weather have been confirmed in Texas and four in Oklahoma. Authorities believe as many nine others remain missing, including five more swept away from homes along the Blanco River earlier this week. Eight others who were tossed into raging waters when their homes were swept away by the historical flood in Wimberley, near Austin, drowned and have been discovered as far down the river as San Marcos, about 20 miles away.

Meanwhile, state and industry officials are calling on farmers, ranchers and landowners whose property runs along each side of the San Marcos and Guadalupe Rivers to join the search for debris that may have washed down the Blanco River in hopes of finding survivors.

Jeff Nunley, executive director, South Texas Cotton and Grain Association, issued a statement late Friday urging anyone who owns or leases property along the Blanco, San Marcos or Guadalupe Rivers in Central Texas to search their property for debris that may have washed downstream in floodwaters.

“Please be aware that debris and victims of the recent Wimberley floods have far exceeded historical limits, traveling down the Blanco River as far as the San Marcos and Guadalupe Rivers,” Nunley said. “We are asking all farmers, ranchers and land owners along the watershed for assistance in searching their properties for signs of debris and to avoid destroying or burning debris piles.

“Rather, we need their assistance in our search efforts, and if something of interest is discovered, please contact local authorities."

Flash flood warnings posted

Texas and Oklahoma, as well as parts of Arkansas, Missouri and Kansas, were under flash flood warnings Friday night, according to the National Weather Service. Those warnings were expected to be extended well into the weekend as more thunderstorms and possible heavy rains were expected both Saturday and Sunday.

On Friday, the White House announced President Obama had signed a disaster declaration for three counties in Central Texas which will make federal assistance available to those affected by the floods.

New evacuation orders were issued Friday evening, the latest for residents living in the City of Wharton near the Colorado River and in low-lying areas subject to flooding. Also in Southeast Texas, four counties adjacent to Wharton issued mandatory evacuations for homes along the flood-swollen Brazos River.

The National Weather Service warns that swollen rivers and saturated ground in parts of the southern Plains increase the chance of flashfloods throughout the weekend and said residents should be aware of road closures and to not attempt to drive into flooded areas.

On Thursday the NWS issued a statement indicating that the month is now officially the wettest May on record. On average, Texas, in spite of its size, has received an equivalent of over eight inches of rain across its 269,000 square miles. Officials say that amount of water is enough to meet all water demand in New York City for seven years, or more water than travels down the Mississippi River and drains into the Gulf of Mexico in a single year.

'Ridiculous amount of rain'

"We have received a ridiculous amount of rain," said Texas State Climatologist John Nielsen-Gammon this week.

He said a combination of an El Niño weather event in the Pacific and a jet stream that seems stuck above the U.S. Southwest is the cause of heavy rains and flooding across the Southwest throughout May.

Because rains have continued to keep farmers out of the fields in wide areas of Texas, county agents say they have few crop damage reports so far. But some farmers have reported lodging from wind and water and flooded fields and others reported hail damage in some areas. But no one is offering a guess as to what lasting damage may be realized as a result of so much water in the fields.

As one South Texas farmer put it, "We're hoping for a couple of dry days that will allow us to get back into the field to get a better handle on all the damage we might have suffered."

For more on the situation in Oklahoma, Texas and other states in the Southwest, visit http://www.weather.com/forecast/regional/news/plains-rain-flood-threat-wettest-may-ranking