Thunder storms and fog are expected to hit Shanghai today after heavy fog early yesterday caused traffic chaos on local highways, restricted shipping traffic and forced the cancelation of more than 150 long-distance bus shuttles.

The Shanghai Meteorological Bureau issued a yellow fog alert at 9:21pm on Sunday which was raised to orange at 11pm.

The fog did not start to disperse until 8am yesterday. At 9:20am the bureau canceled the orange fog alert.

Most areas in the city had visibility under 500 meters. Nanhui District had the lowest visibility of only 50 meters, said the bureau.

"The fog was caused by the warm air mass at the south lower reaches of the Yangtze River," said Xu Jiye, a forecaster with the bureau.

Xu said fog may hit again in some parts of the city today as the warm air mass still cover the area.

Local ports have been kept under restricted shipping traffic since late Sunday evening because of heavy fog, said the local maritime authority.

The Wusong maritime safety administration, in charge of water traffic safety at the mouth of the Yangtze River, said some vessels were ordered to stay at anchor and restrictions were still in place around local banks last night.

Fog also disrupted rush-hour traffic on local major expressways. Police cars were used to lead queuing vehicles on highways and control speeds during the start of rush hour at 7am, the highway authority said.

This year's first thunder storm is expected to fall today, with rain to continue through Friday, under the influence of a cold front, the bureau said.

(Shanghai Daily April 8, 2008)