By Meredith Davis

CHICAGO (Reuters) - Rains and melting snow are expected this weekend to trigger more flooding in parts of Midwest, mainly in Iowa, Illinois and Missouri, adding to concerns over possible delays in spring seedings.

Although sowing of the corn and soybean crops in the Midwest does not begin until next month, the melting of near-record snow in some areas this winter has fanned concerns that seedings could be delayed for a second straight year.

The National Weather Service issued several flood warnings for the Midwest, mainly Iowa, Illinois, and Missouri, where melting snow and rain are causing extremely soggy conditions.

Chicago Board of Trade corn and soybean futures, which rallied on Wednesday due to concerns over possible delays in seedings, were down on Thursday as the dollar rose.

"The flooding could be more significant south of Des Moines, Iowa because that is where the heaviest rain is going to be," said Mike Palmerino, a forecaster with DTN Telvent in Boston.

Iowa is typically the top corn and soybean producing state in the country.

A half to 1.5 inches of rain is expected to fall south of Des Moines through Saturday. Conditions should turn dry on Sunday and Monday. Areas north of Des Moines could see 0.10 to 0.50 inch of rain.

The NWS expected moderate to major flooding along several Iowa rivers, some of which are jammed with ice.

The eastern Midwest is expected to be dry through Friday, with rain developing over the weekend. Portions of Illinois could see snow mixed with rain, Palmerino said.

The eastern Midwest will see mild temperatures in the low to mid-60s F (18 C) through Friday, but will dip into the 40s F during the weekend.

"Depending on how much rain we get, we could see flooding increase across the Midwest caused by melting snow, saturated soils and increasing rainfall," Palmerino said.

The southern and central Plains will not escape precipitation this weekend. Portions of the regions could see wet snow on Friday and Saturday with unusually cold temperatures in the 30s F (minus 1 to 4 C). Typically late March temperatures are in the 60s F.

The swollen Red River will continue to be fed by melting snow, with warmer weather forecast through this week.

The river reached 33.37 feet at Fargo, the biggest city in the Red River Valley straddling North Dakota and Minnesota.

The river has risen nearly 2 feet since Wednesday and is expected to crest at 38 to 39 feet this weekend. It set a flood record of 40.8 feet in 2009.

(Reporting by Meredith Davis; Editing by John Picinich)