The City of London is working as quickly as possible to ensure the heavy rain expected to fall Thursday and Friday will have somewhere to go.

Officials say the rain could result in flooded streets, especially where catch basins are covered in packed snow and leaf debris.

Crews were out early Thursday attempting to clear as many as possible - focusing on high-risk areas - but they are asking for public help.

Where it is safe to do so, residents are asked to clear, or even partially clear, catch basins on quiet local streets and cul-de-sacs.

With more than 26,000 storm grates on city streets, crews will be working through the night to try to prevent streets and basements from flooding.

Residents can also report street flooding during business hours by emailing es@london.ca or calling 519-661-4570, after hours people can call 519-661-4965.

With the anticipated heavy rain, restoration companies like Winmar have brought in extra staff.

"If the rain hits and the weather warms up the way it is supposed to we are ready for about 300 to 600 calls in London alone," says manager Chris Craigan.

But there are things homeowners can do ahead of time to try to prevent water from getting in.

That includes making sure ice hasn't pooled in the eavestrough and "You want to go down and check your sump pump. It hasn't run in two months so you want to pour some water down the well, trigger the float and make sure it discharges the water," Craigan adds.

With all the rain and snow melt, Steve Sauder of the Upper Thames River Conservation Authority says rivers and creeks are expected to swell, especially in low lying areas across the city

"Places like Greenway Park, Harris Park and Gibbons Park, those are low-lying areas that may see some water into those areas over the next couple of days."

And if the parks start to flood, Sauder adds that it's very important for people to keep away because the areas can become extremely dangerous.

"We have unstable ice conditions, we have water getting raised in those areas, the ice is moving away from the bank and creating a very dangerous situation for people, pets and anyone being near those stream areas."

Rainfall warning re-issued on Thursday

Environment Canada is calling for a major storm across southwestern Ontario that could bring 25 to 50 millimetres of rain through Thursday and Friday.

Forecasters say the storm system will bring rising temperatures along with significant precipitation and strong winds.

The highest amounts of rainfall are forecast to be in the Windsor to Sarnia through Niagara to Hamilton corridor and along the north shore of Lake Ontario.

Thunderstorms will also be possible over southwestern ontario, and may result in locally higher rainfall amounts.

Environment Canada adds that significant snow melt due to the rising temperatures will also be a concern.

As the rain comes to an end, winds are expected to increase out of the southwest with gusts to 70 or 80 km/h possible, particularly along the shores of the Great Lakes.