Commuters heading into Chicago Friday morning may not be able to see the skyline very clearly, but it isn't all due to smoke from wildfires impacting air quality.
It's also because of "dense fog," the National Weather Service said.
"Dense fog continues across portions of the area this morning," a Friday morning tweet from the NWS said. "Slow down, increase following distance, and turn on your low-beam headlights if encountering fog during the AM commute!"
Conditions are expected to improve around 9 a.m., the NWS said.
Earlier in the week, Chicago-area residents woke up to wildfire smoke coating the skies, which led to multiple days of air quality alerts, postponed events, hundreds of canceled flights, closed beaches and more.
This weekend, the smoke and air are expected to finally start clearing up, after air quality in the Chicago area, according to the government website AirNow, slid back down to "unhealthy for sensitive groups," which ranks as level three on the site's six-level scale.
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In Northwest Indiana however, an air quality alert remains in effect through midnight Friday. According to the National Weather Service, residents with respiratory issues in Lake, Porter, Newton, Jasper and Benton counties should "limit prolonged outdoor activity."
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And though the air quality in some parts is expected to continue improving, daily scattered storm chances Friday through Sunday could put a damper on holiday travel schedules or plans, including the NASCAR Chicago Street Race scheduled for July 1 and 2.
MORE: Chicago Independence Day Weekend Events Guide: Fests, Fireworks and, Yes, NASCAR
Forecast models show Friday will see some dry parts of the day, in addition to scattered showers and storms, which are expected to roll in after 1 p.m. According to NBC 5 Meteorologist Alicia Roman, some heavy downpours and gusty winds are possible, with the potential for stronger to severe storms south of Interstate 80.
Both Saturday and Sunday are expected to see storm chances as well, although Saturday's afternoon precipitation may stay south of the city. On Sunday, however, a better chance of more widespread rain is expected to move in early and through the morning hours.
Temperatures Friday are expected to be warm and muggy, the NBC 5 Storm Team says, with highs in the mid 80s to low 90s. Weekend temperatures will dip slightly, with highs in the mid 80s Saturday and upper 70s Sunday.
Forecast models show Monday and Tuesday are expected to be clear, dry and warm, with temperatures in the 80s and 90s.
How the weather could impact weekend travel, events
According to AAA, more than 50 million people across the country are expected to hit the roads for the Fourth of the July holiday weekend, with 2.8 million of those people in Illinois alone. When it comes to air travel, the Chicago Department of Aviation says more than 1.49 million passengers are expected to travel through Midway and O'Hare International Airports this weekend.
As of 5:35 a.m. Friday, FlyChicago.com reported 41 cancelations at O'Hare.
For those heading to the NASCAR Chicago Street Race, officials say the races will go on in wet weather, but will likely be unable to go forward if there is standing water or lightning.
MORE: Updated list of NASCAR road closures, construction in and around Grant Park this week
If weather forces a postponement of Saturday's Loop 121 race, that race would likely move to Sunday, which means both races -- the Loop 121 and the Grant Park 220 -- could be conducted on Sunday.
An alternate plan would see one race performed on Monday.
"From a weather perspective, our cars will be able to run in wet weather," NASCAR Chicago Street Race president Julie Geise said. "In the instance of severe weather, lightning, obviously, we would not be able to run the events. We would do everything we can to get those races in Saturday or Sunday."
Additionally, NASCAR officials say they don't expect air quality to be a problem come race day.
"We are definitely monitoring with Illinois EPA," NASCAR and Chicago officials said during press conference earlier this week. "We're also in touch with the National Weather Service in regards to what's going on with the smoke. We don't anticipate being in and then I don't anticipate us being an air quality alert going into the weekend. So if we're not in this air quality alert, then we'll definitely continue to have the NASCAR event as as we see fit."
