A sudden thaw brought with it a thick fog Monday that forced flights in and out of Ottawa to be cancelled or delayed, but conservation experts said the risk of flooding in eastern Ontario is lower than they anticipated.

The experts had feared that as temperatures shot upward, the accumulated snows of recent weeks would cause flooding.

Environment Canada predicted daytime highs well above the melting point Monday, reaching 12 C in Toronto and London, 10 C in Ottawa and 8 C in Kingston and accompanied by rain throughout much of the southern and eastern parts of the province.

Snow from several storms has accumulated throughout Ontario communities, and some of it vapourized into fog as the temperatures rose.

Krista Keely, a spokeswoman for the Ottawa International Airport Authority, urged airline passengers to check the status of their flights before heading to the airport, as the fog prevented many flights from leaving between mid-morning and the early afternoon.

"Visibility's very low. There are a number of cancellations on the board as well as some delays," she said. "And obviously there are some airlines that are hoping the fog will lift soon and they'll be able to be on their way."

Flood risk low

But temperatures are in fact lower than expected and eastern Ontario is now expecting only five to 10 millimetres of rain, leading to a lower risk of flooding than conservation experts had predicted earlier.

"We don't expect that the peak flows will be much above or even get to … an average springtime flow, which means basically no significant flooding of any kind," Patrick Larson, a spokesman for the region's Rideau Valley Conservation Authority, said Monday.

Gord Mountenay, water management supervisor for the nearby Mississippi Valley Conservation Authority, said some roadside ditches could still overflow.

"You could get blockages and flooding along the roads instead of what we would normally be dealing with, which is the rivers and the creeks," he said.

Earlier, the Rideau Valley Conservation Authority warned residents who have had previous problems with flooding to prepare by removing valuables from the basement and ensuring they have sandbags available to protect low-lying garages and below-grade doors. Residents were also urged to keep an eye on their foundations and basement corners where leaks could occur.

Rick Gold, a spokesman for southwestern Ontario's Upper Thames River Conservation Authority, also warned parents to keep their children from the rising water in streams, rivers and ponds, which he predicted will continue to swell throughout the week as temperatures are expected to stay above freezing.

Meanwhile, the Ontario Provincial Police eastern region's snowmobile, all-terrain vehicle and vessel enforcement (SAVE) team issued a warning Monday that the warm weather is making ice on local lakes and rivers unpredictable and dangerous. 

Police emphasized that a minimum of 12 centimetres of "new, clear hard" ice is needed to support a snowmobile or ATV, while 10 centimetres is needed to support one person ice fishing.