The first wave of 300 Canadian military personnel is being sent to British Columbia to help communities overwhelmed by floodwaters as parts of the province are expected to be hit with heavy rain following snowmelt from unseasonably warm weather.

The Canadian Armed Forces said staff from Joint Task Force Pacific and personnel from the 3rd Canadian Division based in Edmonton were to establish themselves in Vernon on Thursday before being deployed to areas affected by flooding including Grand Forks.

Officials in the southern Interior city say thunderstorms are expected to bring a second round of high water.

Chris Marsh of the Regional District of Kootenay Boundary said while water levels in the Granby, Kettle, and West Kettle rivers ebbed since a flood last week, the Kettle River rose 20 to 22 centimetres on Thursday and all three were dangerously high.

"They remain very, very high and of course the threat is that they'll continue to rise until Saturday," Marsh said.

Across the province, about 4,500 people have been forced out of their homes while 7,000 residents have been placed on evacuation alert as the threat of flooding rises, said Chris Duffy, executive director of Emergency Management BC.

Weather will continue to be a big factor into next week, said David Campbell, head of the province's River Forecast Centre.

"The prolonged nature and the severity of the temperatures that we've seen is unprecedented for this time of year and that's leading to flows that we have not seen in many decades," he said, adding weather in the southern parts of the province is the main concern in the short term.

Rain expected Thursday night and into Friday will push the risk of extreme flooding through the Similkameen, Okanagan, Shuswap and Boundary regions, he said.

Ralph Goodale, the federal minister of public safety and emergency preparedness, said in a news release that members of the Armed Forces will help with evacuations, sandbagging and property protection.

B.C. Public Safety Minister Mike Farnworth said military personnel will be deployed to the areas of greatest need, including in the southern Interior.

Frances Maika, corporate communications officer at the Regional District of Kootenay Boundary, said some members of the Armed Forces could be put to work in Grand Forks as another surge of water was expected.

Environment Canada issued special weather statements Thursday, saying as much as 40 millimetres of rain could fall in the area by late Saturday.

"Last week, the Granby station picked up 52 millimetres of rain that was not in the forecast," Maika said. "Sometimes you can get these isolated showers, and if we get that, the river forecast model completely changes."

Celinda Galloway was told to leave her home in the Grand Forks neighbourhood of Ruckle, but she said she and her husband Ryan along with about 20 other residents are staying put in an effort to save their homes.

"Obviously they want us out," she said. "Our homes are salvageable."

Galloway said they built a berm of dirt and sandbags to protect their home, adding they've had some mud and water seep into their basement but damage has otherwise been minimal.

"If we left, nobody would have pumped our basement out."

Maika said she understands residents' frustration in the Ruckle neighbourhood but safety is the main priority.

"It's a low elevation area that was at definite risk of harm coming to people who remained there," she said.

The Regional District of Kootenay Boundary gave residents a 12-hour window to return to their homes to pick up any valuables left behind on Thursday.

A news release from the district says properties along the banks of the surging Kettle River were at risk, and more evacuation orders were possible.

School District 51, which operates eight elementary schools, two secondary schools and a development centre in the Boundary region, closed all schools Thursday because of the potential for more flooding.

A state of local emergency was in effect across the entire neighbouring Regional District of Okanagan-Similkameen, which posted on its website that provincial agencies were closely monitoring the levels of Osoyoos Lake and preparing for evacuation orders if required.

In the Regional District of Central Kootenay, east of Grand Forks, evacuation alerts were expanded along two waterways, while firefighters from across the district were sent to the village of Salmo to help with sandbagging in anticipation of flooding there.