Behind the Forecast: How weather impacts Thunder Over Louisville

Listen to Science Behind the Forecast with Meteorologist Tawana Andrew every Friday on 89.3 WFPL at 7:45 a.m.
Listen to Science Behind the Forecast with Meteorologist Tawana Andrew every Friday on 89.3 WFPL at 7:45 a.m.
Published: Apr. 22, 2022 at 8:51 AM EDT|Updated: Apr. 21, 2023 at 10:01 AM EDT
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LOUISVILLE, Ky. (WAVE) - Thunder Over Louisville is the official kickoff to the Kentucky Derby Festival.

Weather is vital to the show overall, and organizers have specific criteria when planning the air and fireworks shows. We’ve been as cold as 34°F (2005) or as warm as 87°F (2022) on Thunder Day.

Of the 30 full Thunder Over Louisville shows we’ve had since 1990, precipitation has fallen at some point in the day for half of them. In fact, sleet fell at the Louisville International Airport on the day of the first-ever Thunder Over Louisville - the afternoon and evening were dry. Sleet was actually seen along the River during Thunder in 2005.

Clouds can impact the air show, which is required to have a ceiling height of 1000 feet. The National Weather Service defines ceiling height as “the height of the ceiling in feet above ground level (AGL), defined as the lowest broken or overcast cloud deck observed.” In layman’s terms, the ceiling is a measurement of how high above the ground the bottom of the lowest clouds are (the clouds must cover more than half of the sky). When clouds are under 3000 feet, only acts that have a “low” show can perform and no vertical maneuvers are allowed.

Rain usually doesn’t affect the aircraft; those watching the airshow are more impacted by rainfall. If a thunderstorm is nearby, a “no-fly” may be issued. Once the thunderstorm is gone, the show can continue.

When the wind reaches more than 23 MPH, it limits what planes can do during the air show. The wind near the Ohio River is vital to planning, but so is the wind speed at the Louisville Muhammad Ali International Airport. Some of the fastest aircraft in the show use the airport’s longest runway. If the winds are too strong, then longer runaways may be unavailable, grounding some planes. Thunder Over Louisville organizers say that winds over 28 MPH will ground all sky-diving teams.

This year, instead of 75 drones there will be 300 in the drone show before the fireworks. Wind over 25 MPH will limit the drone show.

Rain does not usually delay the fireworks show unless a downpour is expected at the launch time. Severe thunderstorms or tornado warnings will also delay the show. Wind over 23 MPH can distort fireworks patterns. Thunder officials analyze wind speed at launch time to see if a delay is necessary.

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