Quick Summary: Two kinds of weather end a swim day, and each has a clear rule. Storms: clear the water if you see lightning, hear thunder, or the sky looks threatening — the threat reaches roughly six to ten miles from the storm, so thunder means the storm is already in range. Shelter: a substantial building or a hard-topped car with the windows up; dugouts, pavilions and sheds are specifically not safe, and nowhere outdoors is. Restart: at least 30 minutes after the last thunder, and the clock resets on every new rumble. Heat: read the heat index, not the thermometer, and add up to 15°F because the published values assume shade — 90–103°F is Extreme Caution and 103–124°F is Danger. The 911 line: a hot child who is confused or agitated has heatstroke, not heat exhaustion. Download the free printable pool weather go/no-go card here.

The weather rules that actually get followed are the ones decided before anyone is wet. That is not a platitude; it is the National Weather Service’s own diagnosis. Its guidance for organised outdoor activities says plainly that officials without a written plan end up deciding from personal experience or from a desire to finish the activity, and that both put lives at risk. It recommends a plan that gives clear and specific guidelines to eliminate errors in judgement, and that it be followed without exception.

That framing is worth borrowing even if you are one parent with a backyard pool rather than a swim club with a meet schedule. The pressure to finish the game is the same. What follows is the substance of that plan for the two weather hazards that actually close pools — lightning and heat — and the questions to put to whoever is running the pool when it is not your own.

⛈️ At what point does the water have to be cleared?

Earlier than instinct suggests. The National Weather Service gives three criteria for stopping an outdoor activity, any one of which is sufficient on its own. If you see lightning, stop — in clear air, and especially at night, lightning is visible from storms more than ten miles away. If you hear thunder, stop — thunder normally carries about ten miles, and background noise from traffic, wind and rain cuts that down, so if you can hear it at all it is a safe bet the storm is within range. And if the sky simply looks threatening, stop, because storms can develop directly overhead and some produce their first lightning as they arrive.

The distance is the part that surprises people. A significant lightning threat extends roughly six to ten miles outward from the base of a thunderstorm cloud. Sunshine where you are standing is not evidence of anything. This is also the reasoning behind the familiar “30/30” shorthand — count the seconds between the flash and the bang, and act if the gap is under thirty — which is a memorable way of describing the same six-to-ten-mile radius. Our full guide to swimming in a thunderstorm and the 30/30 rule works through the physics and the facility protocols in detail. For the decision itself, you do not need to count at all: hearing thunder has already answered the question.

Two practical notes. Everyone means everyone — wading, sitting on the steps and standing in the shallow end are all in the water. And the exit should be direct. Folding towels, coiling the hose and pulling the pool cover across are twenty or thirty seconds that were not in the plan, and the plan is already tight because the walk to shelter takes time too.

🏠 Which shelters are safe in a thunderstorm, and which are not?

Getting out of the pool is only half of the instruction, and the half that gets forgotten. The National Weather Service’s position is unambiguous: there is no place outside that is safe when a thunderstorm is in the area. Standing on the deck, waiting under a tree or sheltering beside the fence is still outdoors.

What counts as safe is a substantial building with wiring and plumbing — a house, a school, the facility’s own indoor space. In the absence of one, a hard-topped metal vehicle with the windows closed provides good protection. What does not count, and this is stated explicitly, is the category of small outdoor structures: dugouts, rain shelters, picnic pavilions, sheds and the like are not safe. They are also the most common wrong answer a family gets when they ask a camp or a community pool where everyone goes.

Once inside, stay away from windows and doors and from anything that conducts electricity — corded phones, wiring, plumbing, and anything connected to them. Indoor pools sit in an interesting position here: the roof solves the outdoor problem, but a pool is plumbing on a large scale, so the sensible move is to ask the facility what its own storm protocol is rather than assume the building has settled the question. And if you are at a lake, a river or a beach, the swim has to end earlier than at a backyard pool, because shelter is usually further away and swimmers are often a long way from shore. Our open water safety checklist covers how much earlier.

⏱️ How long after the last thunder before swimming resumes?

At least 30 minutes, measured from the last thunder heard or the last flash seen — not from when the rain stopped, and not from when the sky cleared. The reason for measuring it that way is that electrical charge can linger in clouds after a storm has seemingly passed, so a blue sky is not evidence that the storm has finished producing lightning.

The detail that catches people out is that the clock restarts. Every time. One distant rumble at minute twenty-eight buys a fresh thirty minutes, because that rumble is proof the storm is still active. This is why a delay that “should” have been half an hour becomes two hours, and why organised programmes tend to move a session rather than pause it.

Two habits make this survivable. Write down the time of the last thunder rather than trusting memory, because memory under pressure rounds down and always in the wrong direction. And agree a give-up time before the day starts — “if we are still waiting at four, we go home” — so that the decision to abandon the afternoon is made calmly instead of argued about in a car park.

👁️ Who should be assigned to watch the weather?

Somebody specific, and not the person running the activity. This is one of the more useful details in the National Weather Service guidance and one of the least well known: a lightning safety plan should designate someone to monitor the weather, and that monitor should not be the coach, umpire or referee, because those people are busy and cannot adequately monitor conditions. The monitor also has to know the plan’s guidelines and be empowered to enforce them — a watcher who has to persuade somebody senior is not a watcher.

Translated to a pool, that means it should not be the instructor teaching in the water, and it should not be the lifeguard, whose entire job is scanning the water and who should not be looking at the sky instead. At a family pool, it means naming one adult for the afternoon rather than assuming that whoever notices first will say something.

This is the same logic that sits behind the water watcher card for supervision: a responsibility that belongs to everybody in general belongs to nobody in particular. Weather monitoring fails the same way drowning supervision fails, and for the same reason.

🌡️ What heat index is too hot for a swim lesson?

Look up the heat index rather than the temperature, and then correct it for standing in the sun. The heat index — the apparent temperature — combines air temperature with relative humidity, and humidity does roughly half the work. At an air temperature of 100°F the heat index reads 96°F when the air is dry and 124°F when it is humid. A thermometer alone genuinely cannot tell you which of those two days you are having.

The National Weather Service publishes four classifications:

  • Caution, 80–90°F: fatigue possible with prolonged exposure and/or physical activity.
  • Extreme Caution, 90–103°F: heat stroke, heat cramps or heat exhaustion possible with prolonged exposure and/or physical activity.
  • Danger, 103–124°F: heat cramps or heat exhaustion likely, and heat stroke possible with prolonged exposure and/or physical activity.
  • Extreme Danger, 125°F or higher: heat stroke highly likely.

Then the correction that matters most for a pool deck: those published values are calculated for shady locations, and exposure to direct sunlight can increase the heat index by up to 15°F. A deck at noon is not shade. That single adjustment is enough to move an afternoon from Caution into Danger, and it is the reason a day that looks manageable on the forecast can be punishing in practice.

The National Weather Service also publishes HeatRisk, a newer five-level scale from 0 (little to no risk) to 4 (extreme) developed with the CDC. It is worth a look as a second opinion on how hard a given day will be, but treat it as what it says it is: experimental, and explicitly supplementary to official heat watches, warnings and advisories rather than a replacement for them.

🚑 Heat exhaustion or heatstroke: how do you tell them apart?

By behaviour, not by temperature. A child with heat exhaustion is tired, dizzy, headachy, nauseous or irritable, with cool clammy skin and heavy sweating. Move them somewhere cool, take off extra clothing, let them sip cool water if they are alert and not vomiting, and apply cool wet cloths or let them sit in cool — not ice-cold — water. They should start to feel better within about 30 minutes. If they do not, if they get worse, or if they cannot keep fluids down, seek medical care.

A child with heatstroke is confused, agitated or slurring their words, with skin that is hot to the touch (it may be dry, it may still be sweaty) and a body temperature around 104°F (40°C) or higher, and may vomit, have a seizure, or lose consciousness. That is a 911 call. Make it on the confusion — do not go looking for a thermometer first — then keep cooling them while you wait for help. Our detailed guides to heat exhaustion in kids at the pool and heat illness in young swimmers cover the full symptom lists and the response steps.

Two things make heat harder to spot at a pool than anywhere else. A swimming child is already wet, so you cannot read whether they are sweating or have stopped sweating. And heat exhaustion looks like drowning behaviour — clumsy, confused, panicky — which is a good reason to get a child out and assess them on the deck rather than watch from a lounger and wonder. Prevention is a schedule rather than a judgement: water every 20 to 30 minutes whether or not anybody asks, shade breaks, a cap on session length on the worst days, and a proper drink at breakfast rather than a sip on arrival. Our guide to nutrition and hydration for young swimmers covers what to send them with, and the sun safety guide covers the UV half of a hot afternoon.

❓ Which weather questions belong in a swim school policy?

Five, and they are not ours — they are the questions the National Weather Service says a lightning safety plan has to answer. Asking them is simply reading the standard back, and a well-run programme will answer all five without hesitating.

  1. When are activities stopped? You want a criterion, not a philosophy. “First thunder or first flash” is an answer; “when it looks bad” is not.
  2. Where do people go? A named building. If the answer is the pavilion, the cabana or the equipment shed, that is the wrong answer, and it is worth saying so kindly.
  3. When are activities resumed? Thirty minutes after the last thunder, with the clock restarting. Fifteen minutes means somebody has invented their own rule.
  4. Who monitors the weather and makes the call? A designated person who is not teaching, coaching or guarding, and who is empowered to enforce the plan.
  5. What happens if someone is struck? Who calls 911, who starts CPR, where the AED is kept.

Ask about heat in the same conversation, because it has no equivalent published five-question framework and therefore tends to have no policy at all: at what temperature or heat index do sessions shorten, move indoors, or cancel? These belong alongside the other things worth checking before you enrol — our swim school policy fine-print checklist covers make-up credits and cancellations, which is exactly what a weather closure triggers, and the questions to ask your child’s instructor cover the teaching side.

One more thing worth knowing if the worst happens: a lightning victim carries no electrical charge and is safe to touch. Call 911, start CPR if they are not breathing, use an AED if one is available, and keep going until help arrives. Most people struck by lightning survive.

🖨️ Download the pool weather card

One page, both hazards, decided in advance. The card holds the stop criteria for storms, a safe-versus-unsafe shelter table, the restart clock with space to write down the time of the last thunder, the four heat index bands with the direct-sun correction, a heat exhaustion versus heatstroke comparison with the 911 line marked, a hot-day hydration and cooling routine to fill in, the five questions for a swim school or camp, and the six answers that should worry you.

Tape one copy inside the pool gate and keep one in the swim bag. The point of a card is that the argument happens once, in the kitchen, rather than every time the sky changes.

Open the printable pool weather go/no-go card →

Worth saying plainly, because it underlies all of this: a weather rule protects one afternoon, and no weather rule and no number of lessons makes a child drown-proof. Lessons are one layer of protection alongside four-sided pool fencing, constant undistracted supervision within arm’s reach of a young or non-swimming child, properly fitted life jackets in open water, and an adult trained in CPR. The National Weather Service documents about 30 lightning deaths a year in the United States and hundreds more injuries, with roughly two thirds of the deaths connected to outdoor recreation — and almost none of them involve anybody deciding to take a risk. They involve people finishing something. That is what a rule written down in advance is for.

📚 Authoritative Sources

Frequently Asked Questions

How close does a thunderstorm have to be before you clear the pool?

Close enough to hear or see, which is much further away than most people assume. The National Weather Service notes that a significant lightning threat extends roughly six to ten miles out from the base of a thunderstorm cloud, and it gives three criteria for stopping an activity: you see lightning, you hear thunder, or the sky simply looks threatening. Thunder normally carries about ten miles, and traffic, wind and rain shorten that — so if you can hear it at all, the storm is already within range. Lightning is visible from even further in clear air and at night. The familiar 30/30 shorthand, counting the seconds between flash and bang and acting if it is under thirty, describes the same distance in a form that is easy to remember, but you do not have to count: hearing thunder is already the answer. Clear everyone, including children wading or sitting on the steps, and do not stop to fold towels or pull the pool cover across.

Why does the 30-minute wait restart every time?

Because the clock is measuring the storm, not your patience. Experts agree that people should wait at least 30 minutes after the last thunder before resuming outdoor activities, and the reason is that electrical charge lingers in clouds after a storm appears to have passed. A single distant rumble at minute twenty-eight means the storm is still capable of producing lightning, so the wait starts again from that rumble — which is why a delay that should have been half an hour routinely becomes two hours, and why swim meets get moved rather than paused. Write down the time of the last thunder rather than trusting memory, because memory under pressure always rounds in the wrong direction. It also helps to agree a give-up time before the day starts, so that the decision to go home is made calmly rather than argued about in a car park.

Does being under a roof end the storm rule for an indoor pool?

It solves the biggest part of the problem but does not automatically end the question. The National Weather Service is categorical that there is no safe place outdoors during a thunderstorm, and that substantial buildings with wiring and plumbing offer the best protection — so an indoor facility is in a far better position than an outdoor deck. The caveat is that the guidance for people sheltering indoors is to stay away from windows, doors, corded phones, wiring and plumbing, and a swimming pool is plumbing on a large scale. The practical answer is to ask the facility what its own storm protocol is rather than assuming the roof settles it. A well-run indoor programme will have one written down and will not mind being asked. Small outdoor structures are a different matter entirely: dugouts, rain shelters, picnic pavilions and sheds are specifically listed as unsafe, and they are the most common wrong answer a family gets.

What heat index is too hot for children to swim?

Read the heat index rather than the thermometer, then add for the sun. The National Weather Service classifies a heat index of 80–90°F as Caution, where fatigue is possible with prolonged exposure or activity; 90–103°F as Extreme Caution, where heat cramps, heat exhaustion and heat stroke all become possible; 103–124°F as Danger, where cramps or heat exhaustion are likely and heat stroke is possible; and 125°F or higher as Extreme Danger, where heat stroke is highly likely. Two corrections matter for a pool day. First, those published values are calculated for shady locations, and direct sunlight can add up to 15°F — a pool deck at noon is not shade, and that correction alone can move an afternoon from Caution into Danger. Second, humidity does half the work: at an air temperature of 100°F the heat index reads 96°F in dry air and 124°F in humid air, so the thermometer alone cannot tell you which kind of day you are having.

At what point does an overheated child need an ambulance?

When their behaviour changes. Confusion is the line between heat exhaustion and heatstroke. A child with heat exhaustion is tired, dizzy, headachy or nauseous, with cool clammy skin and heavy sweating, and should improve within about 30 minutes of being moved somewhere cool, having extra clothing removed, sipping cool water if they are alert, and having cool wet cloths applied. A child with heatstroke is confused, agitated or slurring, with skin that is hot to the touch — it may be dry or may still be sweaty — and a body temperature around 104°F (40°C) or higher, and may vomit, have a seizure or lose consciousness. That is a 911 call, and it is a call you make on the confusion rather than waiting to find a thermometer. Call first, then keep cooling while you wait. If heat exhaustion does not improve in about half an hour, worsens, or the child cannot keep fluids down, seek medical care as well.

Does being in the pool protect a child from heat illness?

No — and being in the water actively hides the warning signs. A swimming child is already wet, so you cannot see whether they are sweating or whether they have stopped, which is one of the signals you would otherwise be reading. They are also enjoying themselves, moving constantly and unlikely to complain until they are well past comfortable. The American Academy of Pediatrics notes that children overheat faster than adults do, and within any group the youngest child, the newest one and the one working hardest to keep up are all carrying more risk than the average. The practical answer is a schedule rather than a judgement: water every 20 to 30 minutes whether or not anyone asks for it, because thirst already means mild dehydration has begun, plus shade breaks, a cap on session length on the worst days, and a first drink at breakfast rather than a sip at the pool. It is also worth knowing that heat exhaustion looks like drowning behaviour — clumsy, confused and panicky read the same either way, which is a reason to get a child out and assess them on the deck rather than watch and wonder.