Will Later Race Starts Mean More Rain Outs?

Over the years, NASCAR race start times have been moving to later in the day. There’s been a conversation about whether those later start times will increase the likelihood of rain delays.

Here’s the questions we need to answer:

  1. How much later are races starting?
  2. Do chances of rain really increase as it gets later in the day?
  3. Are NASCAR tracks likely to be affected?
  4. Are there other factors in scheduling that preclude moving race times to try to avoid rain?

In everything that follows, I use ‘x PM’ to cover any race start time from x:00 PM to x:59 PM. Also, all times are Eastern because that’s how NASCAR writes them in the schedule.

How Much Later are Race Start Times in 2021?

I’ll compare race start times in 2021 to the 2019 season because the 2020 season was so unusual in terms of scheduling.

Two pie charts comparing the distribution of race start times for 2019 and for 2021nd
  • There are fewer night races (starting times after 6 PM) in 2021 (19.5% vs. 25.0%)
    • We have the same number of races starting at 6 PM, but fewer starting at 7 PM.
    • Some of this decrease is because we have seven road courses on the schedule in 2021. Most road courses are either set up for nighttime driving, with the exception of tracks like Daytona that host 24-hour races.
  • Races are scheduled to start at 1 PM and 4 PM in 2021, whereas no races started at those times in 2019.
  • There are fewer races starting in the 2 PM hour in 2021 relative to 2019: 25% to 38.9%.
  • There are more races starting in the 3 PM hour in 2021: 50% versus 36.1%.
  • Most races both years were scheduled to start between 2 PM and 4 PM.
  • If we add up the percentage of races starting between 2 PM and 4 PM:
    • 75% of the races in 2019 started in this time window
    • 75% of the races in 2021 are scheduled to start in this time window.

So the changes in race start times between 2019 and 2021 isn’t really that big. We’re basically talking about shifts of an hour or two.

Over the last decade and a half, there has been a definite trend toward earlier start time, as you can see below.

A waterfall graph showing how the race start times have changed from 2007-2020
Now that I’ve learned to make waterfall diagrams, I make them every excuse I can get just because I think they look pretty. Note the rainbow ROY G BIV color selection.
  • The total number of night races ( later than 6 PM) has remained relatively constant.
  • Races no longer start before 1 PM Eastern
    • We didn’t have a lot of before-noon races (red)
    • We haven’t had a race start before 1 PM since 2015 (orange)
  • Even starting before 2 PM (yellow) has become rare.
    • The majority of races started between 1 PM and 2 PM in 2010
    • We had no 1 PM races in 2019 and just one in 2021
  • The unusually large number of 4 PM starts in 2020 was an anomaly as NASCAR juggled schedules to get races in at all thanks to COVID.

Is Race-Ending Rain Really More Likely as the Day Goes On?

Showers and drizzles are bad, but tracks recover from them quickly.

Thunderstorms are another thing. They drench the track enough to require Air Titans and jet dryers. Lightening precludes having anyone out there working on drying the track.

There are about 2000 thunderstorms going on around the world at any time. Each is the result of three factors coming together. They are:

  1. Moist Air
  2. Unstable Air Configuration
  3. Lift

Moist Air

This one is a gimme. To have rain, you need moisture in the air. Most of that moisture comes from the evaporation of large bodies of water. You can count Daytona having more moisture in the air than Phoenix. That’s more an issue of location than time.

It’s the next two elements that make the difference between ‘muggy’ and race-threatening rain.

Unstable Air Configuration

If you hold a beach ball underwater, it rises when you let go because the beach ball is less dense than water.

Similarly, warm air is less dense than cold air, so warm air rises.

The normal (stable) configuration is when warm air is on the top and cold air is on the bottom, closest to the ground, as I’ve tried to show in the leftmost illustration in the figure below.

Images showing stable air, unstable air and unstable air plus lift, which is a requirement for thunderstorms
This is obviously way oversimplified, but I think you get the idea.

An unstable configuration is when the warm air is underneath the cool air.

In some cases, the warm air will rise. But as a packet of warm air rises, it cools down. The pressure is lower at higher elevations, which allows the warm air to expand. Expanding air cools. The now-cool air sinks.

But there cases when a packet of warm air stays warm enough as it rises that it keeps rising. It’s a complicated function of how quickly the pressure and temperature change with altitude, as well as with how much water there is in the air.

Let’s say some warm, moist air rises, as I’ve indicated in the right-most picture above. The air rises high enough that the moisture in the air starts to condense. Condensation gives off heat, which keeps the air warm.

So it keeps rising, condensing more water vapor as it goes up and forming clouds — which are just frozen water crystals. Parcels of air just keep going up and up. Cumulonimbus clouds (i.e. thunderclouds) can be 10-12 miles high.


You’ll notice I wrote ‘let’s say that some warm, moist air rises’, without saying why that why that might happen. Lift is a mechanism that starts the initial upward motion.

  • Hills and mountains can cause lift. Air in contact with a mountain warms, starting an upward motion along the mountain.
  • Frontal boundaries are areas where two masses of air with different temperatures (and thus different densities) come together. Colder, denser air acts like a plow, pushing warmer air up. Voila! Lift.
  • Non-uniform heating is a third way to generate lift. A giant section of blacktop heats up much faster than a cornfield. That can cause a pocket of warmer air that will start to rise because of the different densities.

We put all three of these things together and we get a thunderstorm.

Are Thunderstorms More Likely Later in the Day?

Lift and moisture are more dependent on geography and overall weather. Instability is the factor that causes thunderstorms to be more likely in the afternoon and early evening. The Sun has had all day to warm up the air, so instability is highest at these times of the day.

Instability also makes thunderstorms more common in the late spring and summer months. When the overall temperature is low, you’ve got much less likelihood instability.

Is This Really a Problem for NASCAR?

Unlike other series, NASCAR mostly doesn’t race in the rain, so thunderstorms are more of a problem for NASCAR than some other racing series.

But there’s also a geographical issue. 35-45% of NASCAR races are in the southeastern part of the country. And the southeastern part of the country is much more likely to have thunderstorms than any other part of the country, as shown below.

A map of the U.S. showing how many days of thunderstorms areas around the US get each year

The southeast U.S. has two sources of warm moist air: the Atlantic Ocean and the Gulf of Mexico. (California has the Pacific Ocean, but because of the way the ocean currents circulate, they get colder, less-moist air.)

In particular, Florida is a peninsula. These two moisture sources not only combine, they literally run into each other, making Florida the most likely place for thunderstorms in the whole country.

There’s a blip in the number of thunderstorm days in the Rockies. That’s the effect of the mountains, which provide lots of lift. Even though they have less warm, moist air, what air they do have gets lots of encouragement to start thunderstorms.

Are We More Likely to Encounter Rain Delays in 2021?

The shifts toward later start times are pretty minor compared to the variation in the elements we need for a thunderstorm to occur. Local humidity and temperature, along with the weather in the upper atmosphere, vary more than the effect of additional instability due to shifting race times by one or two hours.

So while we may be slightly more likely to encounter rain, it’s going to be a small increase in probability, not a large one.

If only the vortex theory actually worked.

Why Doesn’t NASCAR Schedule to Avoid Rain?

NASCAR definitely considers weather in planning their schedule. We do not race in New Hampshire or Pocono in February. They try to keep drivers out of Daytona and Miami in the daytime heat of the hottest months of the year.

Weather is one of the most complex systems scientists study. Prediction — especially months in advance — is pretty much impossible.

But we have some generalities we can count on. If you start earlier, you’ve got a better chance of finishing the race — or at least getting to halfway — before rain stops the proceedings.

So if you really wanted to avoid rain, you’d start races at 8 a.m. I’m pretty sure that’s not going to happen just because of the impact on television viewing.

And there might be a downside to reaching halfway if you’re the type of fan who favors a delayed race with all laps run over an abbreviated race.

And weather is only one aspect NASCAR has to consider when developing a schedule.

Ever try getting six people to find a meeting time they can all make? NASCAR must juggle 26 different tracks and 36 dates (and that’s just point races).

  • Geography constrains the calendar. Grouping west-coast dates prevents teams from having to a lot of cross-country trips which are exhausting and expensive.
  • At-track scheduling also has to be considered.
    • Even before COVID, NASCAR was moving to decrease the number of days teams had to be at the track to save teams money. There are a lot of one-day events on the 2021 schedule.
    • Inspection takes time. With a one-day show, you can’t start a race at noon unless everyone shows up at the track at zero-dark-thirty. And the last thing you want is people who haven’t gotten enough sleep working on racecars.
  • NASCAR’s move to later start times is recognition that it has a nationwide fan base. A noon eastern race is 9 AM Pacific time. People in California are in church, sleeping in, enjoying pancakes with the kids… Later start times help get more eyes on the sport.
  • NASCAR’s television partners have an even bigger juggling act because they’re scheduling multiple sports. As seasons elongate, there are more and more conflicts.


If NASCAR wanted to minimize the chances of rain-shortened or delayed races, they’d have to sacrifice other things, like viewership, venues or cost. The later start times only increase the chances of a rainout by a small percent, which is small compared to other weather aspects that can’t be controlled or predicted.

As with everything in life — as my father always told me — the NASCAR schedule is a compromise.

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