Weather & Wellness Wednesday: Beware of the Rush-Hour Rumblers!

This past Friday marked the first official day of summer. I actually love the heat and humidity of Gulf Coast summers (I know...I’m an anomaly). I am always happy on a bright, sunny day, and I find comfort in the stillness of warm, humid summer evenings. But I am well aware that summer brings a mix of joys and hazards.

There are some summer health risks that we hear about often:

• Powerful UV rays can cause sunburns and increase the risk of skin cancer.
• Exposure to heat and humidity can lead to heat-related illnesses.
• Ground-level ozone caused by the combination of sunshine and pollutants such as car exhaust can be harmful to those with respiratory illnesses.

However, there is one summer hazard that I feel is often overlooked, but it is so fascinating that I’ve given it a name: The Rush-Hour Rumbler.

What Is a Rush-Hour Rumbler?

“Rush-Hour Rumbler” is my nickname for the quickly forming isolated thunderstorms that occur like clockwork between 3pm and 6pm on hot summer days. Unfortunately, these storms form right as people are leaving work, picking up kids from school, or heading out to run errands. They are typically referred to as 'pop-up thunderstorms' or 'popcorn storms' due to how quickly they form and how randomly they seem to appear. But I think that the term “Rush Hour Rumbler” captures both the timing and the impact of these storms (and be honest...who doesn’t like a little alliteration?)

You may be familiar with this weather pattern, especially if you live in the south or along the coast:

1. The day starts out clear, hot, and sunny.
2. By mid-afternoon, cotton-like cumulus clouds begin to gather in the sky and begin to grow tall.
3. By late afternoon, the blue skies have turned dark and ominous, and suddenly, there’s heavy rain, wind, and lightning.
4. After about a half hour of atmospheric chaos, the skies clear, and if you are lucky, you may catch a late evening rainbow!

Rush-Hour Rumblers are usually brief, but they can be intense, and can reach severe limits. They create a perfect recipe for hazardous travel because they occur at peak travel times.

What Are Some Sources For These Storms?

Daytime Heating (Convection): On summer afternoons, the sun heats the ground and the air above it. Warm, moist air rises and cools as it ascends, forming towering cumulonimbus clouds. If the atmosphere is unstable this convection leads to thunderstorms.

Sea-Breeze Convergence: In coastal areas, a sea breeze can push moist ocean air inland, where it collides with warmer air over land. This upward lift often sparks thunderstorms, especially in the late afternoon hours.

Outflow Boundaries:  Thunderstorm outflow is cool air that spread down and out from a storm.  An outflow boundary separates the thunderstorm-cooled air from the surrounding air.  When these boundaries collide with warm surface air, or other outflow boundaries, they create lift which can result in new thunderstorms.  (Weather Nerd Note: This process is very cool to watch on a radar loop!)

"Ring of Fire":  During the summer, large areas of high pressure can form and result in extreme heat.  This area is sometimes referred to as a "heat dome".  Thunderstorms can form and rotate around the edges of the high pressure system where the air is unstable and uplifted.   

Urban Heat Island Effects:  Cities tend to be hotter than surrounding rural areas due to buildings, roads, and infrastructure absorbing and re-radiating heat.  Some studies suggest this added heat and rising motion can trigger storms or intensify ones that move overhead.  

These late morning cumulus clouds signal rising heat.
 By late afternoon, they can develop into towering storms.

The Safety Hazards of Rush-Hour Rumblers

Let's look at why Rush-Hour Rumblers matter for public health and safety:

Hazardous Driving Conditions

• Sudden downpours reduce visibility and create slick roads.

• Storms during peak traffic times increase the risk of car accidents.

Strong Wind Gusts

• Winds can down tree limbs or blow debris into roadways.

• These obstructions are especially dangerous when visibility is already low due to heavy rain.

Lightning Strikes

• Even short-lived storms can produce frequent lightning.

• While it may be rare for vehicles to be struck by lightning, lightning risks are especially dangerous for people who are outdoors during the storm (parking lots, bus stops, etc.)

Flash Flooding

• Rush-Hour Rumblers can drop several inches of rain in under an hour.

• Urban drainage systems can be overwhelmed, leading to ponding or flooding, especially on low-lying roads and underpasses.

• Flash flooding can result in car stalls, or even worse, the car could be swept into a larger body of water (stream, canal, lake, etc.)

Staying Safe during Rush-Hour Rumblers Season

Whether you're commuting from work, picking up kids, or enjoying outdoor recreation, here’s how to stay safe when Rush-Hour Rumblers arrive.

• Know your routes: Avoid flood-prone areas and learn alternate routes.

• Check the forecast: Use weather apps and radar to stay informed.

• Sign up for weather alerts: Local emergency alert systems and weather apps can notify you of nearby storms.

• Wait it out in a safe space: If a storm approaches, stay put until it passes instead of heading to the car to try to “beat the rain.”

Remember: Never drive into floodwaters! 

Just 6 inches can knock over an adult, and 12 inches can move a car.

Do you have Rush-Hour Rumblers in your area during the summer? Share your insights in the comments below!

Sources:

https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/

https://www.noaa.gov/jetstream/ocean/sea-breeze

https://www.theweatherprediction.com/habyhints/6/

https://www.sciencedirect.com/science/article/abs/pii/S135223109900374X