Rockyview's fire chief Ken McMullen says firefighters and water pumps are on standby. (CBC)

A rainfall warning remains in effect for much of the southwestern part of Alberta, with more than 50 millimetres expected to fall by Friday.

A slow moving storm is crossing Southern Alberta Thursday, heading to southern Saskatchewan, according to Environment Canada.

The province issued a high streamflow advisory for the Elbow River on Thursday. 

And in Calgary, the fire department is warning against boating on the Elbow River because the gates of the Glenmore dam will be opened, increasing the river's flow.

Days of cold, wet weather have people living in Bragg Creek, west of Calgary, bracing for the worst.

Rocky View County's fire chief Ken McMullen spent Thursday checking water levels and flow on the Elbow River. Firefighters and water pumps are on standby. McMullen said he is concerned about the rain and the snow melting in the mountains upstream.

"The significant issue is how much of this snow pack is going to come off at once. It has risen considerably from the last time I was here," he said.

The Elbow River backs onto Laurel Frezell's yard and she says the flow has gotten much faster and the water level higher this week.

"I keep the kids away from the river. They're not allowed down by the river right now because it's running so fast, you just don't know what's going to happen."

If it gets much higher, Frizell says she'll start thinking about sandbagging.

The rain prompted a high stream flow advisory for southwestern Alberta on Wednesday, although flooding is not expected.

Calgary soaked

In Calgary, the ground is already saturated thanks to 20 to 40 millimetres of rain falling on the city over the past few days.

From noon to 3 p.m. on Thursday, the airport saw 9.2 millimetres, while Canada Olympic Park got 22.9 millimetres.

Another 40 to 50 millimetres is possible before Friday night, with most of it falling Thursday night and into Friday morning. The result could be basement flooding, said CBC weather specialist Danielle Savoni.

"When the soil is saturated, there is nowhere for this water to go but up," she said, adding that this is a lot of rain to fall in a short period.

But it could be worse, Savoni said. Last year Calgary got almost 20 centimetres of snow from May 27 to 29.