With a frigid Alberta clipper ravaging Southwestern Ontario last night, treacherous roads and slip-sliding motorists filled ditches with vehicles. The clipper, a cold weather front that rapidly makes its way across the Prairies to Ontario, is responsible for the heavy snow that's burdened motorists this week.

Drivers have "just got to slow down for the ice," Const. Rick Schut of the OPP said yesterday.

Parts of the London area were clobbered by up to 20 centimetres of snow, with a 40-per-cent chance of flurries today. With temperatures staying cold, expect a a low of -24 -- which, with the wind chill factored in, will feel colder than -30.

Yesterday, snow and biting cold across the region caused traffic chaos:

- A pickup truck near Lucknow struck a school bus when the bus stopped to pick up a student. Police said the bus was carrying 10 students but no one was hurt.

- One person was seriously hurt in a late-afternoon, three-vehicle collision in Essex County, said Schut.

- Near Waterloo, a pair of late-afternoon crashes on Highway 401 blocked two lanes, backing up traffic for kilometres in both directions.

London police reported no major accidents but said many vehicles wound up in ditches because of poor road conditions.

With temperatures last night expected around the -20 mark, the London-Middlesex Health Unit issued another cold weather alert.

Slippery roads also made it difficult for those wanting a cab yesterday. "In some areas of the city, there's an hour wait," said Brenda Day, a dispatcher at U Need A Cab.

Tomorrow could bring some relief, with slightly milder temperatures forecast -- a high of -10 and a low of -14.