Flooded areas of the northern suburbs that dodged a bullet on Thursday might not be as lucky this weekend, with severe storms and heavy rains forecast Friday evening and overnight.

That could mean already high rivers could continue to overflow their banks.

“We are watching weather forecasts closely,” a statement on the Lake County government Facebook page said. “The storms that passed through Lake County on Thursday brought less than an inch of rain and did not have any real effect on river levels.

“The primary concern today is the uncertainty of the weekend weather forecast, which calls for a potential of severe storms overnight Friday and into Saturday. . . . The three-day forecast shows a total of two to three inches of rain. As a result, there is a significant threat of localized flooding/flash flooding, and the potential for increased river levels depending on the placement of the storm.”

The National Weather Service agrees with that wet assessment. A flood warning continues along the Des Plaines River in Lake and northern Cook counties; and along the Fox River in Kane, Kendall and McHenry counties until further notice.

“Moderate flooding is occurring along the Des Plaines and Fox, and more moderate flooding is forecast,” the weather service said.

A severe thunderstorm watch was issued for much of northeastern Illinois until midnight Friday; and a severe thunderstorm warning is in effect for northeastern DuPage and northwestern Cook counties until 5:30 p.m. The worst of the storm was over the Palatine and Arlington Heights areas as of 4:55 p.m., with Schaumburg, Park Ridge and Oak Park also in the immediate path of the storm.

A flash flood watch will also be in effect for Lake, Cook, DuPage, Kane, Kendall, McHenry, Will and Grundy counties, along with most of northeastern Illinois and southeastern Wisconsin, from 4 p.m. Friday through Saturday morning.

Multiple rounds of thunderstorms, each capable of producing rainfall of over one inch per hour, are expected across north central and northeast Illinois late Friday afternoon through early Saturday morning, according to the weather service.

That means “concerns are increasing for damaging winds across northern Illinois and northwest Indiana, followed by storms capable of torrential rainfall across the flash flood warning area.”

Additional heavy rains could “exacerbate flooding already occurring across northern Illinois, producing new rises on already swollen rivers and creeks,” the weather service said. With the ground saturated, heavy rains could quickly produce runoff and flash flooding.

There is a 70 percent chance of rain Friday night and early Saturday in the Chicago area, while that rises to a 75 percent chance in the Rockford area.

A statement on the Village of Algonquin website warned residents that “a flood with the potential to damage property is likely and that sandbagging is encouraged directly … At this time, the village does not see an immediate need to leave the area, but residents are encouraged to monitor the quickly changing conditions and to take appropriate actions, including possible relocation.”

The Des Plaines River at Des Plaines was at 17.67 feet as of 11:30 a.m. Friday, after rising to over 18 feet following the rain Thursday morning. The river crested at 19.83 feet last Sunday, and was expected to rise to about 17.7 feet by noon Sunday. Flood stage is 15 feet.

At Gurnee, the Des Plaines was at 9.59 feet as of 11:30 a.m. Friday. It crested at 12.09 feet Monday, and was expected reach 9.9 feet by early Monday morning. Flood stage is 7 feet.

Many roads near the water remained closed on Friday, and several Pace bus routes were being detoured.

Many roads and parks remain closed in Algonquin, where sandbagging efforts are being ramped up in anticipation of possible heavy rains Friday night. | Algonquin Police Dept.

On the Fox River, things appeared more dire, with the river at 12.53 feet as of 11:30 a.m. Friday, after cresting at 12.82 feet early Thursday. It is expected to reach 12.8 feet again by noon Saturday. Flood stage is 9.5 feet.

The Village of Algonquin posted a message on its website calling for volunteers to help with sandbagging efforts as property owners brace for more flooding.

Volunteers were asked to go to the Public Works Facility at 110 Meyer Dr. until 5 p.m. Friday, and from 9 a.m. to 5 p.m. Saturday and Sunday to either help fill sandbags or help property owners sandbag their homes.

Street closures remain in place on several roads close to waterways, and Cornish, Towne and Riverfront parks are also closed.

The Towne Park closure has forced the 57th annual Founders Day Festival, scheduled for July 27-30, to be moved to Algonquin Lakes Park at 1401 Compton Dr.

The first night of the Mount Prospect Downtown Summer Block Partywas also canceled Friday due to threat of dangerous weather. The fetival will continue on Saturday.

At the McHenry Lock/Dam, where flood stage is 4 feet, the Fox was at 7.42 feet at 11:15 a.m. Friday after cresting at 7.52 feet on Thursday.

Sandbags are ready to be deployed on La Fox River Drive in Algonquin, on Thursday, where residents are bracing for another round of heavy rains that could raise the swollen Fox River even higher Friday night and Saturday morning. | Rick West/Daily Herald via AP

All that water also means a lot of mosquitoes.

“Floodwater mosquitoes are now hatching in the area,” Michael Adam, senior biologist for the Lake County Health Department and Community Health Centers, said in a statement Friday. “These aggressive biters are reaching nuisance population levels in the county, but do not carry West Nile virus.”

The greater concern, he said, is that standing water, such as in buckets, gutters, plant containers, flood debris and other items, “can become breeding sites for Culex mosquitoes, which are the primary carriers of West Nile. We need everyone to eliminate stagnant water from  properties to keep these mosquitoes at bay.”

That became even more urgent when a batch of mosquitoes, sampled July 14 in Zion, tested positive this week for West Nile virus. It it the first confirmed indicator of the virus in Lake County in 2017.

“In 2016, there were two human cases of West Nile virus confirmed in Lake County,” Mark Pfister, executive director of the health department, said. “Hot weather and standing water create the ideal conditions for mosquitoes to breed. Residents need to take action to protect themselves from mosquito bites.”

For those impacted by flooding seeking resources or services, the Multi-Agency Resource Center opened Friday at 965 E. Rollins Rd. in  Round Lake Beach. It was scheduled to be open until 6 p.m. Friday, but “for safety reasons” was closing early due to the threat of severe weather. It is scheduled to reopen from 9 a.m.-noon Saturday.

Residents affected by the flooding can meet regional and statewide disaster organizations, including the Red Cross, Salvation Army, Illinois Department of Insurance and other groups for assistance and information. Information on clean-up assistance will be provided, and the health department will have free water testing kits for those with wells.

The Salvation Army has also set up a toll-free Donation Hotline at (888) 369-1349 for those who wish to donate items.

Gov. Bruce Rauner also announced that the state will waive penalties and interest for taxpayers who cannot file or pay property taxes on time as a result of the floods for taxes payable July 11 and Dec. 31.

“Our communities dealing with the unprecedented flooding in northern Illinois should focus on their loved ones and neighbors, not tax deadlines,” Rauner said. “Once these impacted families and businesses have had the time to recover, they can gather the necessary paperwork and file their returns and pay taxes.”

Four counties have been added to a state disaster proclamation, including Cook, Kane, Lake and McHenry.