Across the Midwest and Mississippi Valley, millions of people braced for a volatile evening Monday, as fast-moving storms brought the potential for strong, long-track tornadoes.

Power outages plagued Michigan, Indiana and Missouri, while Illinois was hit hardest by flight cancellations and delays.

For the full forecast from the severe threat, check here.

Below are our updates from throughout the afternoon and evening Monday:

(09:01 p.m. EDT) What To Expect Tonight

From meteorologist Sara Tonks:

Storms are still moving through areas at risk of severe weather, and the threat does continue overnight for many major cities.

A tornado watch with a Particularly Dangerous Situation tag is in effect in northeastern Arkansas, southeastern Missouri, southern Illinois, southern Indiana, western Tennessee and western Kentucky until 11 p.m. CDT. Several tornadoes, a few of which could be intense, are likely, and anyone in the area should have a reliable way of getting severe weather alerts in place before going to bed.

Severe thunderstorms are possible in parts of Texas, Oklahoma, Arkansas, Indiana, Kentucky and Ohio into the early morning hours of Tuesday. Winds gusting up to 70 miles per hour and hail up to 2.5 inches in diameter are possible across the regions as the storms move through overnight.

(08:21 p.m. EDT) Some First Damage Looks

Often with these severe weather threats, we don’t get a lot of insight into the worst of the damage until the next day.

That said, we’re keeping our eyes peeled this evening for any impacts we can share with you, like this tree downed in Louisville, Kentucky.

(08:06 p.m. EDT) Storms Delaying Start of Angels-White Sox Game

The start of the Angels vs. White Sox game in Chicago is being delayed as a result of the weather tonight.

This is the first matchup of the season between the two clubs. The White Sox are hoping to get the game going by 8 p.m. CT.

(07:50 p.m. EDT) Severe Thunderstorm Timing Tonight

Let’s take a look at the timing we can expect as the night progresses. The National Weather Service office in Paducah, Kentucky put together this potential timeline for the areas likely to be affected later tonight.

Note: Times are listed in Central Daylight Time.

(07:22 p.m. EDT) Yes Cap: Why Storms Are Struggling To Fire Up

From meteorologist Sara Tonks:

There is a layer of air acting to limit severe weather from firing up across parts of the Midwest and Ohio Valley, which is something meteorologists refer to as a “cap”.

Thunderstorms are the result of air moving upward in the atmosphere, cooling, condensing and producing precipitation. The stronger the upward movement, the stronger the updraft and therefore the stronger the storm.

One of the main drivers of that upward vertical movement is temperature, since hot air rises.

But if there is a layer of warm air aloft, that rising air gets blocked. It’s no longer warmer than the surrounding air, so it doesn’t rise.

This is the cap.

When that pocket of air does get past that barrier, it has access to large amounts of energy and enhanced vertical motion because it is much warmer than the surrounding air again. Storms can then fire up very quickly and can be intense.

This can happen if the surface air warms enough to surpass that layer (air cools as it rises, so if it’s warmer to begin with at the surface, it might not cool to a point that it is cooler than the cap).

The passage of a frontal boundary can also force air to rise, potentially forcing it past that cap and causing storms to kick off.

(06:59 p.m. EDT) Your Cheat Sheet For Watches And Warnings

Since many of you checking back here for updates are likely under some sort of watch or warning tonight, it’s important to review exactly what those warnings mean.

First, take a look at meteorologist Caitlin Kaiser’s video here. She explains how a “watch” is like when you’re preparing the ingredients for a taco, while a “warning” is like when that taco is put together and ready to be eaten.

When it comes to those warnings, meteorologist Jennifer Gray has you covered. She breaks down how a regular tornado warning can be radar-based or physically spotted, but higher-level alerts like a PDS warning or a tornado emergency mean a confirmed storm is already causing serious or catastrophic damage.

Just remember: No matter the type of watch or warning, you shouldn’t wait. Every tornado alert is serious and a sign to take safety precautions right away.

(06:33 p.m. EDT) Latest Tornado Warning

A Tornado Warning is in effect for Jacksonville, South Jacksonville, and Virginia, Illinois until 6:00 p.m. local time, impacting a region with more than 37,000 residents.

People in these areas should stay alert and be prepared to take shelter immediately if conditions worsen or a tornado is spotted.

In addition to the tornado threat, hail up to the size of half dollars is possible.

(06:07 p.m. EDT) Hail 3.5 Inches In Size Reported In Missouri

From meteorologist Sara Tonks:

Hail nearing softball-sized was reported near Versailles, Missouri, this afternoon from a strong thunderstorm moving through the region.

For reference, a 3-inch hailstone can fall as fast as 107 miles per hour and requires an updraft of 84 miles per hour, so this hailstone was likely riding an updraft above the fastest speed limit in the United States (85 miles per hour, on Highway 130 in Texas).

(MORE: 5 Things You Should Know About Hail)

(05:38 p.m. EDT) Power Outage Updates

From meteorologist Sara Tonks:

Power outage numbers are starting to tick up across the mid-Mississippi Valley and Midwest as strong storms continue to impact the region, and over 130,000 customers are now without power across the regions.

Here’s the breakdown by state:

• Michigan: 54,800+
• Wisconsin: 40,900+
• Indiana: 30,000+
• Illinois: 20,000+
• Arkansas: 10,200+
• Missouri: 7,800+

(05:13 p.m. EDT) Hail In Chesterfield, Missouri

From Content Writer Ada Wood:

In this footage shared on Twitter, a resident of Chesterfield, Missouri, which is west of St. Louis, shows hail raining down near a home.

The National Weather Service (NWS) warned of tennis-ball-sized hail, “several” likely tornadoes. and widespread gusts up to 75 mph as severe storms are anticipated through Monday afternoon. A tornado watch is in effect for St. Louis County until 9 p.m., per the NWS.

(04:37 p.m. EDT) Flood Threat For Mid-Mississippi, Ohio Valleys

From Meteorologist Sara Tonks:

In addition to the threat of severe storms, there is a potential for flash flooding across the mid-Mississippi and Ohio Valleys today as strong storms dump a large amount of rainfall in a short period of time, with rainfall rates reaching 1 to 2 inches per hour.

Rivers across the Central Plains are in moderate flood stage as of Monday afternoon, and monitoring stations across the Ohio Valley are likely to peak in a minor flood stage later this week as water continues to flow downstream.

The threat shifts Tuesday to stretch across the Southern Plains and Deep South into the Tennessee Valley as rainfall totals climb towards 5 or 6 inches.

(04:12 p.m. EDT) Chicago Tops The Misery Map

Travel disruptions are piling up in Chicago as storms intensify there.

According to flight tracker FlightAware, Chicago-area airports are now leading the nation in delays and cancellations.

This likely means a long night ahead of waits, missed connections and changing schedules as severe weather continues to impact one of the country’s busiest air travel hubs.

(03:58 p.m. EDT) Power Outages On The Board

We’re seeing some storm-related power outages tick up in Missouri, where severe weather is making its way across the state.

Randolph, Howard and St. Louis counties have been the hardest hit so far, according to PowerOutage.us.

(03:26 p.m. EDT) What To Expect From Today’s Threat

From meteorologist Sara Tonks:

The same active pattern that caused a violent EF-4 tornado last week in Oklahoma is continuing today as a storm system encounters significant instability in the central U.S., focusing on the mid-Mississippi Valley.

Storms have already started to pop up now, but the threat doesn’t peak until later this evening for cities like St. Louis, Memphis and Chicago.

The region is facing the threat of potential violent, long-lived tornadoes, meaning EF-3 or higher ratings that are capable of staying on the ground for extended periods of time, especially in the mid-Missisippi Valley bullseye, where there is a level 2 of 3 intensity threat.

Widespread damaging winds are also possible in the region along with large to very large hail.

(03:13 p.m. EDT) Tornado Warning Issued For Metro St. Louis

A tornado warning has been issued for St. Louis, Missouri and the surrounding area.

This is an immediate safety situation. Conditions suggest a tornado could be on the ground or develop at any moment. Quarter-sized hail is also possible.

(03:02 p.m. EDT) Ongoing Tornado Warning

A tornado warning is now in effect for parts of southern Illinois, including Greenville, Pocahontas, and Alhambra, where a radar-indicated tornado has been detected.

Pea-sized hail and strong winds are also possible over the next 45 minutes.

(02:53 p.m. EDT) TORCON Upped To 7 In Some Areas For Tonight

Eastern Missouri and Southern Illinois are in the area of highest threat for today.

(02:30 p.m. EDT) If You’re Stuck Outside When A Tornado Strikes

For those facing the risk of tornadoes today, it’s important to prepare for all scenarios.

If you see a tornado while driving or outdoors, and can’t get to sturdy shelter, here’s what to do:

• Get low in a ditch or depression and protect your head and neck from flying debris
• Never shelter under an overpass. It’s a myth that these provide safety during a storm.
• Don’t rely on tornado sirens alone. Instead, have all of your wireless emergency alerts turned on and stay aware as conditions can change rapidly.

Click here for a deeper breakdown of what to do if you’re caught without shelter during a storm.