Lightning Distance Flash-to-Bang Calculator for US Thunderstorm Safety
The most complete free lightning distance calculator in the US. Built-in stopwatch: tap Flash when you see lightning, tap Bang when you hear thunder, get the distance instantly. Multi-strike storm tracker shows whether your storm is approaching or receding. Includes the NOAA 30-30 Rule, a 30-minute re-entry countdown timer, OSHA 3863 occupational thresholds, NWS verified fatality data through 2026, and activity risk rankings from the National Lightning Safety Council.
Use the stopwatch or enter your flash-to-bang time to instantly see lightning distance, risk level, storm tracking, and NOAA 30-30 rule status.
Lightning Distance and the Flash-to-Bang Method: What Every American Needs to Know Before Going Outside
Lightning is simultaneously one of the most spectacular and most dangerous natural phenomena in the United States. Every single year, between 14 and 21 Americans are killed by lightning strikes, according to verified data published by the National Weather Service at weather.gov/safety/lightning-fatalities. The NWS reports 12 fatalities through June 30, 2026, 21 in 2025, 14 in both 2024 and 2023, and 20 in 2022. The encouraging trend is that improved safety awareness, driven largely by NOAA’s national “When Thunder Roars, Go Indoors” campaign and the adoption of the 30-30 rule, has reduced annual fatalities dramatically from the 1950s and 1960s when hundreds of Americans died from lightning each year. But the danger is far from eliminated, particularly for outdoor workers, anglers, golfers, hikers, and anyone who spends significant time outdoors during the summer months.
The flash-to-bang method is the simplest, most reliable tool you have when caught outdoors during a thunderstorm without access to a weather radar. The physics is elegant: light from a lightning flash reaches your eyes essentially instantaneously because it travels at roughly 186,000 miles per second, meaning the flash is simultaneous with the strike for all practical purposes at any distance a person might be from a storm. Sound, however, travels at only about 750 miles per hour through air, or roughly one mile every five seconds. By counting the seconds between the flash and the thunder, you are measuring how far away that lightning bolt actually struck. That time gap, divided by the speed of sound at your current air temperature, gives you the distance. This calculator does all of that math automatically, while also tracking whether your storm is getting closer or moving away.
Why the Five-Second Rule Is an Approximation, Not a Constant
The classic rule of thumb that every five seconds between flash and bang equals one mile is based on the speed of sound at approximately 20°C (68°F). At that temperature, sound travels 343.2 meters per second, which works out to 4.69 seconds per mile or 2.91 seconds per kilometer. But the speed of sound changes with temperature. NOAA’s JetStream learning resource on thunder and the speed of sound states that the speed of sound in dry air equals 331.3 times the square root of (1 plus air temperature in Celsius divided by 273.15). On a hot Texas summer afternoon at 35°C (95°F), sound travels at about 352 meters per second, which means a five-second count corresponds to 1.09 miles rather than exactly one mile. On a cold autumn morning at 5°C (41°F), sound travels at about 334 meters per second, so a five-second count corresponds to only 1.04 miles. For most practical safety purposes, these differences are minor: what matters far more than the exact distance is whether your count is above or below 30 seconds, which is the NOAA and OSHA threshold for seeking immediate shelter. This calculator corrects for temperature automatically using the NOAA JetStream formula.
The Multi-Strike Storm Tracker: Is the Storm Moving Toward You?
No other free lightning distance calculator on the internet includes a multi-strike storm tracker, and it is arguably the most operationally useful feature for anyone who needs to make real decisions about shelter timing. When you observe consecutive lightning flashes during a storm, each flash-to-bang reading tells you how far away that individual bolt struck. If your second reading is significantly shorter than your first, the storm is approaching. If your second reading is longer, the storm is moving away. If readings stay roughly constant, the storm is moving roughly parallel to your location. This calculator logs up to 10 consecutive readings and displays the trend automatically, so a coach on a baseball field, a ranger at a campground, or a supervisor on a construction site can make informed decisions about when to shelter and when conditions are improving.
The Physics of Flash-to-Bang: Speed of Sound, Temperature, and Distance
The NOAA JetStream Speed of Sound Formula
NOAA’s educational JetStream website and NASA’s Glenn Research Center both verify the same temperature-dependent formula for the speed of sound in air. The formula uses the ratio of the actual temperature to absolute zero temperature (273.15 Kelvin), which emerges from the kinetic theory of ideal gases: the speed at which air molecules collide and transmit a pressure wave scales with the square root of their thermal energy, which itself is proportional to absolute temperature.
v = 331.3 * sqrt(1 + T_C / 273.15) [m/s, exact square-root formula]
/* Linear approximation (accurate within 0.5 m/s up to 50°C): */
v ≈ 331.3 + 0.606 * T_C [m/s]
/* Example values: */
At 0°C (32°F): v = 331.3 m/s = 1,086 ft/s = 740.5 mph
At 20°C (68°F): v = 343.2 m/s = 1,126 ft/s = 767.3 mph ← standard
At 35°C (95°F): v = 351.9 m/s = 1,155 ft/s = 787.3 mph
/* Flash-to-Bang Distance: */
d_meters = v * t_seconds
d_miles = d_meters / 1609.344
d_km = d_meters / 1000
/* 5-Second Rule (NOAA NWS) – at 20°C exactly: */
Sec per mile = 1609.344 / 343.2 = 4.69 sec/mile
Sec per km = 1000 / 343.2 = 2.91 sec/km
/* At 35°C: 1609.344/351.9 = 4.57 sec/mile – storm slightly closer than rule suggests */
Why Thunder Rumbles Instead of Just Crackling
If lightning were a point source, you would hear a single sharp crack of thunder from any distance. The extended rumble you actually hear results from the geometry of a lightning bolt. A typical cloud-to-ground lightning channel is anywhere from a few hundred feet to several miles long. The thunder from the bottom of the channel, closest to you, arrives first. The thunder from the top of the channel, which may be two or three miles farther away even for a strike directly overhead, arrives seconds later. Sound from different segments of the channel takes different amounts of time to reach your ears, spreading out a single lightning event into a rolling, rumbling sound that can last five to fifteen seconds. NOAA’s JetStream page on the “Sound of Thunder” explains this geometry in detail and confirms that a very sharp, nearby crack of thunder indicates a strike that was very close and probably nearly directly overhead, while a long rolling rumble typically means the lightning channel extended significantly in the sky and portions of it were at varying distances from your position.
Verified NOAA and OSHA Lightning Safety Data for the United States
NOAA Flash-to-Bang Distance Reference (Temperature-Corrected)
| Seconds | Distance at 0°C | Distance at 20°C | Distance at 35°C | NOAA Risk Level | Required Action |
|---|---|---|---|---|---|
| 0 (simultaneous) | Within direct strike zone | EXTREME | Possible direct strike. Seek shelter immediately. | ||
| 5 | 1.03 mi / 1.66 km | 1.07 mi / 1.72 km | 1.09 mi / 1.76 km | EXTREME DANGER | Under 1.1 miles. Go indoors NOW. (NOAA) |
| 10 | 2.06 mi / 3.31 km | 2.13 mi / 3.43 km | 2.19 mi / 3.52 km | CRITICAL | Under 2.2 miles. Immediate shelter required. |
| 15 | 3.09 mi / 4.97 km | 3.20 mi / 5.15 km | 3.28 mi / 5.28 km | DANGER | 30-30 rule in effect. Shelter NOW. OSHA: stop work. |
| 20 | 4.12 mi / 6.63 km | 4.26 mi / 6.86 km | 4.37 mi / 7.04 km | DANGER | 30-30 rule in effect. Must seek shelter immediately. |
| 25 | 5.15 mi / 8.29 km | 5.33 mi / 8.58 km | 5.47 mi / 8.80 km | DANGER | Within 30-second threshold. Shelter now. |
| 30 (threshold) | 6.18 mi / 9.94 km | 6.40 mi / 10.30 km | 6.56 mi / 10.56 km | CAUTION | 30-30 Rule boundary. Begin moving toward shelter. |
| 45 | 9.27 mi / 14.9 km | 9.59 mi / 15.4 km | 9.85 mi / 15.8 km | CAUTION | Monitor. Storms move 25+ mph; distance can close fast. |
| 60 | 12.4 mi / 19.9 km | 12.8 mi / 20.6 km | 13.1 mi / 21.1 km | MONITOR | Monitor weather radar. Bolt-from-blue risk above 10 mi. |
| >60 (no thunder) | Thunder not audible beyond ~10 miles (atmospheric refraction) | BOLT-FROM-BLUE | NOAA: lightning can strike 10 mi from rain without audible thunder. | ||
Sources: NOAA NWS JetStream “Learning Lesson: Determining Distance to a Thunderstorm” (noaa.gov); OSHA Fact Sheet 3863 Lightning Safety When Working Outdoors (weather.gov/media/owlie/OSHA_FS-3863_Lightning_Safety_05-2016.pdf).
NWS Verified Annual US Lightning Fatalities (weather.gov/safety/lightning-fatalities)
| Year | US Fatalities | Note | Source |
|---|---|---|---|
| 2026 (prelim.) | 12 | Data through 6/30/2026 per NWS | NWS / NLSC (Jensenius) |
| 2025 | 21 | Lightning activity at 8-year US high in 2025 | NWS / NLSC |
| 2024 | 14 | Below 10-year average of ~22 | NWS / NLSC |
| 2023 | 14 | Second-lowest since 2001 (tied with 2024) | NWS / NLSC |
| 2022 | 20 | Near average; Florida highest state | NWS / NLSC |
| 2021 | 11 | Lowest since 2001 | NWS / NLSC |
| 2016 | 40 | Highest in recent decade | NWS / NLSC |
| 2006-2026 total | ~500+ | Direct lightning fatalities; ~2/3 during outdoor leisure activities | NWS / NLSC (Jensenius) |
Top US States for Lightning Fatalities (1959-2023, NWS/NLSC Verified)
| Rank | State | Fatalities (1959-2023) | Why High Risk |
|---|---|---|---|
| 1 | Florida | 523 | Most afternoon thunderstorms in the US; high outdoor tourism; peninsula geography |
| 2 | Texas | 236 | Large land area; frequent spring/summer storms; high agriculture and outdoor work |
| 3 | North Carolina | 205 | Frequent summer storms; Blue Ridge Mountains; outdoor recreation |
| 4 | Ohio | 151 | High storm frequency; large rural/agricultural population |
| 5 | Colorado | 150 | Afternoon mountain thunderstorms; hiking/climbing; Denver elevation |
| 6 | Louisiana | 147 | 4th in lightning strikes (2025); Gulf moisture; frequent severe weather |
| 7 | New York | 146 | Large population; outdoor summer activities; Adirondacks |
| 8 | Tennessee | 144 | Appalachian ridge-and-valley topography; outdoor recreation |
Sources: NWS weather.gov/lzk/ltgsafety.htm (1959-2023 state fatality table); National Lightning Safety Council lightningsafetycouncil.org. State rankings verified 2025-2026.
Activity Risk Data (NLSC/OSHA 3863 Verified 2025)
| Activity Category | Risk Level | Notes | Source |
|---|---|---|---|
| Fishing (boat/shore) | Highest | Most common outdoor leisure activity in US lightning deaths (NLSC 2025) | NLSC 2006-2025 |
| Beach / Water activities | Extremely High | Open water, no shelter, high exposure. Never swim during thunderstorms. | NLSC 2006-2025 |
| Camping / Hiking | Very High | Remote locations, no shelter access. Tent provides ZERO protection. | NLSC 2006-2025 |
| Golf | Very High | Open course, elevated clubs, slow play: all raise risk. Many courses have lightning detection. | NLSC; Golf Digest |
| Farming / Ranching | 34% of work-related | Open fields, equipment, no shelter nearby. Highest work-related category. | OSHA 3863 (2016) |
| Roofing | 15% of work-related | Elevated, metal fasteners, no shelter: major occupational hazard. | OSHA 3863 (2016) |
| Construction | 11% of work-related | Cranes, scaffolding, metal equipment. OSHA crane-specific lightning rules apply. | OSHA 3863 (2016) |
| Lawn Care / Landscaping | 9% of work-related | Open areas, metal tools. Many incidents occur after storms appear to have passed. | OSHA 3863 (2016) |
| Organized Sports (youth) | High | Coaches and referees must have written lightning safety plans. Stop at first thunder. | NLSC; NWS |
| Indoors (no shelter plan) | Lower but not zero | Lightning can travel through electrical systems and plumbing. Avoid these during storms. | NOAA Lightning Safety |
Three Real US Lightning Safety Examples Using the Flash-to-Bang Calculator
The 30-30 Rule in Youth Sports: When to Stop Play and When to Return
A youth baseball coach in Tampa, Florida, is managing a Saturday afternoon game when a line of afternoon thunderstorms typical of Florida’s summer pattern begins building to the west. Tampa is located in what NOAA calls the “lightning capital of the US,” with more lightning strikes per square mile than almost anywhere else in the country. Florida has accumulated 523 lightning fatalities since 1959, the most of any state. The coach sees a brilliant flash across the western sky and immediately starts counting. He hears thunder 18 seconds later.
Air temperature: 90°F (32.2°C)
Speed of sound at 32.2°C: 331.3 * sqrt(1 + 32.2/273.15) = 349.6 m/s
Distance = 349.6 * 18 = 6,293 meters = 3.91 miles / 6.29 km
30-30 Rule: 18 seconds is UNDER 30 seconds → SHELTER IMMEDIATELY
OSHA 3863: Any audible thunder = stop all outdoor activity NOW
Second reading 4 minutes later: 11 seconds
Distance: 349.6 * 11 = 3,846 m = 2.39 miles
Storm trend: APPROACHING (3.91 mi → 2.39 mi = closing 1.5 miles in 4 min)
Estimated storm speed: ~22 mph
Afternoon Thunderstorms Above Treeline: The Hiker’s Flash-to-Bang Protocol
A hiking group is on the exposed rocky ridge of South Arapaho Peak west of Boulder, Colorado, at approximately 13,400 feet elevation, when cumulus clouds that were small and innocuous at 9 AM begin building rapidly into a classic Rocky Mountain afternoon thunderstorm by 1 PM. Colorado has recorded 150 lightning fatalities since 1959 and frequently produces afternoon thunderstorms above treeline between 1 PM and 4 PM throughout the summer. A lone hiker remains at the summit while the more experienced members of the group are already descending. One member at treeline counts 8 seconds from a flash to thunder.
Temperature at treeline (11,000 ft): approximately 12°C (54°F)
Speed of sound at 12°C: 331.3 * sqrt(1 + 12/273.15) = 338.9 m/s
Distance = 338.9 * 8 = 2,711 meters = 1.69 miles / 2.71 km
30-30 Rule: 8 sec WELL under 30 sec → EXTREME DANGER
Action: CROUCH DOWN, leave ridge immediately, get below treeline
Note: At altitude, lower air density and temperature reduce sound speed
Standard 5-sec rule (343 m/s) would give 1.73 miles
Corrected: 1.69 miles – storm is slightly closer than rule suggests at cold temp
OSHA 3863 Compliance on a Roofing Job: The Outdoor Worker Protocol
A roofing crew supervisor in Houston, Texas, is overseeing a team installing metal roofing panels on a commercial building. Texas has recorded 236 lightning fatalities since 1959, second only to Florida. The crew is 22 feet above ground on metal panels when the site weather monitor, per OSHA and NOAA recommendations, begins tracking an approaching storm cell. A bright flash appears to the southwest and one crew member counts seconds until thunder.
Air temperature: 88°F (31.1°C)
Speed of sound at 31.1°C: 331.3 * sqrt(1+31.1/273.15) = 348.9 m/s
Distance = 348.9 * 22 = 7,676 meters = 4.77 miles / 7.68 km
30-30 Rule: 22 sec under 30 sec → SHELTER NOW
OSHA 3863: Any audible thunder = STOP WORK IMMEDIATELY
Shelter: Move crew to nearest fully enclosed building (site trailer not adequate)
Roofing crew must descend and enter the building under construction
or move to hard-topped vehicles with windows up
Second reading 6 minutes later from shelter: 11 sec = 2.38 miles
Storm APPROACHING at ~24 mph – would have been on-site within 12 minutes
Six Expert Tips for Lightning Safety in the United States
NOAA Lightning Safety explicitly warns that lightning can and does strike up to 10 miles from the nearest rain and even from areas with a clear sky above. This phenomenon, sometimes colloquially called “bolt from the blue,” occurs when the lightning channel within the storm is nearly horizontal before turning downward to strike the ground far from the storm’s visible precipitation. NOAA notes that thunder cannot be heard beyond approximately 10 miles because the sound refracts upward into the atmosphere before reaching the ground, which means you could be within the bolt-from-the-blue strike zone of a storm and hear no thunder at all. If you can see a distant thunderstorm that appears to be moving toward you, or if you can see lightning even without hearing thunder, you are potentially at risk. The practical rule from NOAA’s national safety campaign: “When Thunder Roars, Go Indoors.” Any audible thunder, no matter how distant, means the storm is already within strike range. Do not wait until the lightning appears close or until rain starts falling to seek shelter.
NOAA’s data shows that a disproportionate number of lightning fatalities occur either as people are moving toward shelter or as they are returning outside before a storm has fully cleared. The 30-minute wait after the last thunder is not a conservative estimate: it reflects the actual structure of dissipating thunderstorm cells, which can continue to produce lightning well after the heaviest rain and most visible activity appears to have ended. The trailing lightning in a dissipating cell tends to be less frequent but can still be highly dangerous because the storm has moved on and people assume it is safe to go back outside. Using the 30-minute re-entry countdown timer in this calculator starting from the last observed thunder ensures you meet the NOAA and OSHA 3863 standard. OSHA specifically requires that outdoor workers remain sheltered for at least 30 minutes after the last thunder before resuming work, and employers should have this standard documented in a written lightning safety plan.
The National Lightning Safety Council and the National Weather Service jointly recommend that any organization responsible for outdoor activities with groups of people, including youth sports leagues, summer camps, golf courses, outdoor festivals, and construction sites, have a documented lightning safety plan rather than relying on informal judgment calls in the moment. A proper plan designates specific shelter locations before any event, establishes a clear trigger threshold (the NOAA 30-30 rule is the standard recommendation), assigns responsibility for monitoring weather conditions, and defines the re-entry protocol. Several major organizations including the American Meteorological Society, the American Red Cross, and the National Lightning Safety Council publish standardized lightning safety protocols for organized outdoor activities. Having a plan and practicing it with participants dramatically reduces the hesitation that causes many lightning injuries: people often wait too long to seek shelter because they don’t want to disrupt an event and there is no clear leader or plan in place. The flash-to-bang method and the 30-30 rule are the operational core of most of these plans.
The most dangerous moments during a storm often involve ambiguity about whether the storm is approaching or moving away. A single flash-to-bang reading of 25 seconds tells you the storm is uncomfortably close but doesn’t tell you which direction it is moving. If your next reading five minutes later is 18 seconds, the storm is definitely approaching and you need to seek shelter without further delay. If your next reading is 35 seconds, the storm is moving away and you can begin the 30-minute countdown from the last thunder. Using this calculator’s multi-strike tracker to log consecutive readings during a storm gives you genuine situational awareness that allows you to make better decisions. Thunderstorm cells in the United States typically move at 15 to 35 miles per hour in the absence of strong steering flow, with some slow-moving training storms capable of staying nearly stationary for hours. Knowing whether your storm is 25 miles per hour approaching or 25 miles per hour receding makes a significant difference in how urgently you need to act.
While a direct lightning strike is immediately lethal and receives the most attention, the majority of lightning injuries outdoors are caused by ground current: the electrical charge that spreads outward from a lightning strike point along the ground surface. A person standing 50 feet from where lightning strikes the earth may be injured or killed by ground current traveling through the soil, particularly on wet ground. This is why the NOAA-recommended position for someone caught in the open without shelter, a position of absolute last resort, is to crouch low on the balls of both feet with feet together rather than lying flat: lying flat maximizes your body’s contact with the ground and the potential voltage difference across your body from ground current. Never hold onto metal objects. If you are in a group, spread out so that a single lightning strike cannot incapacitate all members simultaneously. Move away from any water, from elevated terrain, and from isolated trees, which are themselves primary strike attractors and secondary ground-current sources. But always remember: a building or vehicle is infinitely safer than any outdoor position, and reaching shelter should always be the priority before worrying about outdoor lightning position.
The flash-to-bang method is a valuable safety tool but has several limitations that Perry Weather and NOAA meteorologists have specifically documented. First, the method only works for lightning within roughly 10 miles because thunder cannot be heard beyond that distance due to atmospheric refraction. If you see lightning and hear no thunder, the storm could still be within the 10-mile bolt-from-the-blue strike zone. Second, the method tells you how far away the last bolt struck, not how far away the storm is as a whole: the storm extends in all directions from any specific bolt, meaning the storm center and its future track may bring lightning much closer. Third, human reaction time and counting accuracy introduce measurement errors of two to five seconds easily, corresponding to errors of 0.5 to 1 mile in distance. Fourth, the method cannot account for lightning from storms that have not yet produced thunder near your location. For operational safety decisions beyond the flash-to-bang method, NOAA’s weather.gov radar, the NWS text-based forecasts, and commercial lightning detection networks used by major venues and outdoor operators provide more complete situational awareness. The flash-to-bang calculator is a valuable field tool but should supplement rather than replace weather monitoring.
Quick Reference: NOAA and OSHA Lightning Safety Thresholds
| Threshold / Rule | Value | Meaning | Source |
|---|---|---|---|
| 30-30 Rule: shelter trigger | 30 seconds or less | Thunder within 30 sec = storm within 6 miles → seek shelter NOW | NOAA; OSHA 3863 |
| 30-30 Rule: re-entry wait | 30 minutes | Wait 30 min after LAST thunder before returning outdoors | NOAA; OSHA 3863 |
| 5-second rule | 5 sec = ~1 mile | Quick mental estimate at standard temperature (20°C/68°F) | NOAA NWS JetStream |
| 3-second rule | 3 sec = ~1 km | Quick metric estimate at standard temperature | NOAA NWS JetStream |
| Bolt-from-blue range | Up to 10 miles | Lightning can strike 10 miles from rain without audible thunder | NOAA; OSHA 3863 |
| Thunder audibility limit | ~10 miles | Thunder refracts upward; not audible beyond ~10 miles | NOAA NWS |
| OSHA work-stop trigger | Any audible thunder | Any thunder = stop outdoor work immediately (OSHA 3863 / NOAA) | OSHA Fact Sheet 3863 |
| Speed of sound at 20°C | 343.2 m/s | NOAA JetStream formula: 331.3*sqrt(1+20/273.15) | NOAA JetStream; NASA Glenn |
| Speed of sound at 0°C | 331.3 m/s | Minimum standard atmospheric value | NOAA JetStream |
| Speed of sound at 35°C | 351.9 m/s | Hot summer day: slightly faster, storm slightly farther | NOAA JetStream formula |
| US annual fatalities average | ~20/year | 10-year NWS average; declining from 50+/year in 1960s-80s | NWS / NLSC (Jensenius) |
| Primary shelter: buildings | Rank 1 | Fully enclosed building with wiring and plumbing (NOAA/OSHA) | NOAA; OSHA 3863 |
| Secondary shelter: vehicles | Rank 2 | Hard-topped vehicle, windows up; NOT convertibles or golf carts | NOAA; OSHA 3863 |
| Hearing-impaired cue | See a Flash, Dash Inside | NOAA alternative to “When Thunder Roars, Go Indoors” | NOAA Lightning Safety |
16 Frequently Asked Questions About Lightning Distance and Flash-to-Bang Safety
Related Weather Hub and Safety Calculators for Complete Storm Situational Awareness
Lightning distance is one critical piece of thunderstorm situational awareness. These Weather Hub calculators provide the complete picture for storm spotters, outdoor safety officers, pilots, and weather enthusiasts.
This calculator is provided for educational, reference, and planning purposes only. Speed of sound formula follows NOAA NWS JetStream and NASA Glenn Research Center verified values. The 30-30 Rule is sourced from NOAA noaa.gov/jetstream/lightning/lightning-safety (updated June 22, 2026). OSHA occupational thresholds are from OSHA Fact Sheet 3863, co-published by OSHA and NOAA, available at weather.gov. Annual fatality data is from the NWS verified page weather.gov/safety/lightning-fatalities (updated 6/30/2026) and the National Lightning Safety Council. State fatality data from NWS regional office data (weather.gov/lzk/ltgsafety.htm). Activity fatality data from NLSC and OSHA 3863 (2006-2025). USCalculators.com is not affiliated with NOAA, the NWS, OSHA, or the National Lightning Safety Council. This calculator is NOT a substitute for official NOAA weather forecasts, lightning detection systems, or emergency services. In any life-threatening lightning situation, call 911 immediately. Flash-to-bang estimates have inherent accuracy limitations due to human reaction time, thunder path geometry, and atmospheric variability. Always err on the side of caution: when thunder roars, go indoors. Last reviewed: 2026.