Dirty rain falls across southern Manitoba as dust storm mixes with wet weather

A rare bout of dirty rain hit southern Manitoba Thursday as blowing dust mixed with showers during a powerful windstorm.

Southern Manitoba saw an unusual round of “dirty rain” Thursday as strong winds lofted dust into the air and mixed it with wet weather, leaving dark, muddy residue on vehicles and other outdoor surfaces.

Environment Canada issued blowing dust and wind warnings for large parts of southern Manitoba and Saskatchewan on Thursday afternoon. The national weather agency said blowing dust was expected to persist for much of the day before winds eased later in the evening.

West winds with gusts up to 90 kilometres per hour were expected to reduce visibility in some areas and contribute to poor air quality, the agency said.

The murky rain forms when dust is blown into the atmosphere and then combines with rain before falling back to the ground, University of Manitoba climatologist Alex Crawford told CBC Manitoba’s afternoon radio program Up to Speed.

“That might be in the cloud itself. It might be as the raindrops are falling down and kind of intercept that dust on the way down,” Crawford said. When the water evaporates from surfaces such as cars or houses, he said, the dust is left behind.

Crawford said Thursday’s storm was unusually strong for Winnipeg at this time of year, with atmospheric pressure measured at 981 hectopascals. Lower pressure generally corresponds with stronger storms, and that reading is lower than about 90 per cent of storms Winnipeg typically sees around this season, he said.

While high winds are needed to produce dirty rain, Crawford said the larger factor appeared to be the storm’s reach. Using wind-pattern tracking, he said he could trace air movement from Wyoming toward Winnipeg, allowing dust from drought-affected areas of the western United States, including eastern Wyoming and western Nebraska, to be carried north.

Dust in the air can aggravate conditions for some people, especially those with breathing problems. But Crawford said the dirty rain itself does not appear to pose a significant added danger beyond ordinary atmospheric dust.

The immediate concern remained the weather conditions tied to the storm: reduced visibility, poor air quality and strong winds until the system weakened later Thursday.