Chicago Weather

Timeline: What to expect with multiple rounds of storms possible for start of holiday weekend

A severe thunderstorm watch was issued for much of the Chicago area Friday and will last for several hours, bringing with it much uncertainty

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With much of the Chicago area already under a severe weather alert as an intensifying line of storms races toward northern Illinois, what can you expect and when as Memorial Day weekend begins?

A severe thunderstorm watch was issued for much of the Chicago area Friday and will last for several hours, bringing with it much uncertainty.

Here's a look at what to know about the forecast:

Friday morning

All of northern Illinois was placed under a severe thunderstorm watch until 1 p.m., according to the Storm Prediction Center.

The National Weather Service warned around 6:45 a.m. that a line of severe storms would move into northern Illinois "within the next few hours" and that line carries with it the threat for damaging winds, large hail, and possibly tornadoes. The biggest threat will take place through 9 a.m. in areas along and west of Interstate 39, however.

"Have multiple ways to get warnings," NWS tweeted.

NBC 5 Storm Team Meteorologist Alicia Roman said the morning thunderstorm watch was tied to a line of storms moving across central Iowa, sparking thunderstorm warnings and even tornado warnings as it went.

"This line of storms has really been holding together and racing across Iowa," Roman said. "And that has been the big question. The thinking was that it wouldn't really hold together in a line like this, that maybe part of it would split to north."

But that didn't happen. Roman said instead, the storm "intensified" and is now "sticking together."

"So now we're going to see that moving through our area through the morning hours," she said.

Friday afternoon and evening

The watch comes after the Chicago area was placed a “slight” risk of severe weather Friday, with the arrival time of the system threatening to disrupt travel via airports and roadways.

According to the Storm Prediction Center, that “slight” risk, a level two out of five, covers much of the Chicago area and northwest Indiana, with all manner of severe weather threats possible on Friday. Portions of far western DeKalb and LaSalle counties, however, were upgraded to an enhanced risk for severe weather.

Roman said storm storms will likely threaten gusty and damaging winds, but there remains potential for hail and possibly even tornadoes.

"It's low, but it's not zero heading into the afternoon," Roman said.

Despite Friday morning's watch, the National Weather Service continued to forecast another chance for severe weather Friday afternoon and evening.

"While storms may occur this morning, additional storms with a higher chance for severe weather will occur this afternoon and evening," the NWS tweeted.

But just before 8 a.m., they noted that the morning system could "modulate" any potential storms forecast for the afternoon and evening, adding that it "greatly increases uncertainty."

The NBC 5 Storm Team’s forecast modeling originally showed a cold front rapidly approaching the Chicago area on Friday afternoon, right around the time that many residents will be traveling for the long holiday weekend.

Thunderstorms could impact area airports, as ground stops could either hold planes at their points of departure or prevent flights from leaving O’Hare and Midway in the mid-to-late afternoon.

Another round of showers and storms could arrive in the evening, though they’ll likely be more scattered in nature, according to forecast models.

Once the front passes through, temperatures are expected to cool, with highs in the upper-70s on Saturday under partly-to-mostly sunny skies. Sunday will see another chance of scattered showers and thunderstorms, with that system sticking around through Monday morning.

Highs are expected to settle into the low-70s on both days, with pleasant conditions expected once the quick-hitting system moves through.

You can follow all the latest developments, live radar and more on the NBC Chicago app, and with the NBC 5 Storm Team on television and our 24/7 streaming service.

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