Low clouds moved in on Chicago Saturday afternoon covering much of the city’s skyline, while incoming storms were expected to bring heavy downpours and flash flooding across the city after dark, according to the National Weather Service Chicago.

Multiple rounds of thunderstorms tonight were expected to drop one to two inches of rain on the Chicagoland area, causing floods with fast moving water that could knock pedestrians off their feet and sweep vehicles away or leave them stuck on impassable roads, the weather service said.

The weather service issued a Flash Flood Watch Saturday afternoon for Chicago and portions of northeast Illinois and northwest Indiana. Residents of the affected areas were advised to sign up for flood alerts, know which roads were likely to flood and seek out alternate routes.

As storms increase in coverage over the region after dark, there will be a likelihood of storms with heavy downpours. There is a flash flooding threat for the highlighted area. Rain should diminish in coverage early Sunday morning. #ilwx #inwx https://t.co/0Pq2b87TRE pic.twitter.com/V10iYMODZX — NWS Chicago (@NWSChicago) May 12, 2018

The watch will remain in effect until Sunday morning.

Rain early Saturday brought clouds as low as 400 feet to the downtown area. The cloudy coverage cleared by the early evening to reveal the top and bottom of the skyline, but more rain overnight is expected to bring dark, low clouds back for most of Sunday, the weather service said.

Temperatures were expected to be in the low to mid 50s Sunday, with rain through the early morning.