CHICAGO - RAIN and rapidly rising temperatures accompanied by thick fog threatened to cause flooding on Saturday in the US Midwest after days of Arctic cold, heavy snow and ice.

Thick ice on roads that contributed to dozens of deaths had thawed and mountains of snow turned into pools and streams of water.

'We're getting rid of one problem, the ice, but we're getting another problem with the flooding,' said Ms Marisa Kollias, spokesman for the Illinois Department of Transportation.

The National Weather Service posted flood watches and warnings Saturday for parts of Illinois, Iowa, Wisconsin, Indiana, Michigan and Missouri. As much as 2 inches of rain fell in two hours during the night in west-central Illinois, the National Weather Service reported Saturday.

And as warm air collided with cold, the weather service posted tornado watches for parts of Oklahoma, Arkansas, Missouri, Illinois and Kansas.

After subzero temperatures Fahrenheit (below minus 18 Celsius) in places earlier in the week, Saturday morning readings were in the 40s F (5 to 10 degress C) as far north as Cheboygan, Michigan, at the top of the state's Lower Peninsula, the weather service said.

The weather service said the Chariton River was overflowing and causing minor flooding in Chariton, Iowa. Flood stage is 4.5 metres; the river was at 5 metres at 3 am Saturday and expected to rise a bit more. It said road flooding was reported in parts of Missouri.

Around Chicago, Cook County authorities offered sandbags to communities that needed to fortify low-lying areas, county spokesman Sean Howard said.

Hundreds of people spent the night at Chicago's Midway Airport, where all 82 flights on Friday evening were canceled as the thick fog rolled in. There were also more than 400 flight cancelations at O'Hare International Airport, the second busiest US airport.

Temperatures also were rising in the Pacific Northwest, which has been pummeled by deep snow.

In Portland a couple of inches of rain through Saturday was expected to wash away much of the 19 inches of snow that by one measurement had made December the city's snowiest month since January 1950.

Seattle was also threatened with minor flooding as melting snow overwhelms drains and creeks, said meteorologist Johnny Burg.

In eastern Washington state, however, as much as 4 more inches of snow was possible in Spokane by Saturday afternoon. As of Christmas Day, 46.2 inches of snow had fallen in the area, breaking the December record of 42.7 inches , set in 1996.

Slippery roads and cold have been blamed for at least 43 deaths this week: 11 in Indiana; eight in Wisconsin; five in Ohio; four each in Kentucky, Michigan and Missouri; two in Kansas; and one apiece in Illinois, Oklahoma, Iowa, Massachusetts and West Virginia. -- AP