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A fallen tree blocks Bannerman Avenue at Main Street in Winnipeg on Tuesday afternoon. ((Ismaila Alfa/CBC))

A powerful storm is shouldering into southern Manitoba and bringing the first significant snowfall of the season.

The low-pressure system, heading into the province from central Minnesota, will not only knock temperatures lower but likely send a few election signs and Halloween decorations soaring with winds gusting close to 80 km/h in some parts.

A snowfall warning has been issued for all areas west of Lake Winnipegosis and Lake Manitoba. South of the lakes, the warning stretches east into the Brandon-Carberry-Treherne region.

Rain has already been soaking most of those areas, but the system is expected to intensify later in the day, drawing in colder air and turning the rain into snow.

The snow will be wet and melting at first but will start to accumulate Tuesday night as temperatures drop to the freezing mark, according to Environment Canada.

The snow is expected to continue into Wednesday before tapering off that evening. Generally, snowfall amounts of 10 to 15 cm are expected over the warning area by Wednesday, but higher amounts of 25 cm are possible in the higher elevations of Riding Mountain, Duck Mountain and Turtle Mountain.

'Treacherous' travel conditions

In addition to the snow, strong northerly winds will reduce visibilities, Environment Canada said.

"This will be the season's first major blast of winter weather over southern Manitoba, so residents planning on travel through western Manitoba [Tuesday night] or Wednesday should be prepared for treacherous winter travel conditions, including on the Yellowhead and Trans-Canada highways west of Portage la Prairie," stated a warning from Environment Canada.

The precipitation is expected to stay mainly as rain over the Red River Valley and southeast Manitoba on Tuesday. However, the rain might change to wet snow during the day Wednesday with some slushy accumulations possible by evening.

Beginning Tuesday afternoon in Winnipeg, the winds will be blasting from the northeast at 50 km/h and gusting to 70. On Wednesday, the wind will come from the northwest at 60 km/h, gusting to 80.

The forecast high for Tuesday is 14 C, but the temperature will plummet to 4 C on Wednesday and further drop to 1 C for Thursday. It's not expected to get much warmer than the freezing mark on Friday.

While civic election day on Wednesday will be miserable, the weather should improve for Halloween night in Winnipeg with a forecast high of 9 C.