How to protect your car from hail, and what will not protect it at all.

Usually between fifteen and sixty minutes of useful, specific warning, and sometimes a good deal less. That is the number to plan around, and it is the reason almost every decision on this page is about where the car is rather than what is draped over it.

The longer signal comes earlier. A severe thunderstorm watch, issued by the Storm Prediction Center, tends to arrive hours ahead and covers a wide area: conditions are favourable, nothing is happening yet. That is your planning window, not your action window. Use it to decide where the car will go, not to go there.

The action window is the severe thunderstorm warning from the National Weather Service Fort Worth office, which covers a specific polygon and typically runs thirty to sixty minutes. Warnings for storms capable of large hail state the expected stone size. Golf ball, roughly 1.75 inches, is where sheet metal starts taking dents in numbers. Quarter size, one inch, is the severe threshold and can still mark a soft aluminium hood.

In practice a storm crossing the Metroplex from the west moves at highway speed. If it is over Weatherford and you are in Plano, you have well under an hour, and part of that hour will disappear into traffic and indecision. Decide in advance where the car goes when the phone buzzes. That single piece of preparation does more than any cover ever will.

• Turn on Wireless Emergency Alerts on your phone, and add a radar app that pushes warnings rather than one you have to open.
• Know your county. Warnings are issued by polygon, but the county name is what you will hear first: Collin, Denton, Dallas, Tarrant, Rockwall.
• Decide the destination now, in daylight, when you are not deciding anything under pressure.

Anywhere with a concrete deck over it, and in the Metroplex that mostly means public garages, hospital garages, mall structures, airport terminal garages and office decks that stay open outside business hours. The nearest one is almost always better than the best one further away.

Work it out before the sky changes. Open a map, search for parking garages within about ten minutes of home and ten minutes of work, and check two things for each: is the entrance open at night and on weekends, and does the barrier require a card. A garage you cannot get into at nine on a Tuesday evening is not shelter.

Failing a garage, take the next best thing in this order: your own garage with the junk moved out, a carport, a covered patio, a petrol station canopy, a drive-through lane, a bank drive-up awning, a car wash bay, or the lee side of a tall building with the storm coming from the other direction. Wind-driven hail arrives at an angle, so a wall on the upwind side genuinely reduces what lands on the panels.

Trees are not shelter. A mature canopy stops some stones and drops branches on the roof instead, and hail storms in North Texas travel with the straight-line winds that bring limbs down. Parking under a tree in a severe warning trades many small dents for the chance of one very large repair.

We keep a working list of covered parking across the Metroplex by area, including which suburbs have almost none, on the covered parking page.

A purpose-built, inflatable or thickly padded hail cover works, if it is fitted and secured before the wind arrives. Almost everything else people improvise is either useless or worse than nothing. Here is the honest verdict on each.

Commercial hail covers, the padded or air-inflated kind, are the only category that reliably reduces damage. The good ones use several inches of foam or an inflated bladder, cover the roof, bonnet and boot, and strap under the vehicle. They cost real money, they take five to fifteen minutes to fit, and they are worth having only if you can commit to fitting them in that window. The thin quilted covers sold as hail protection are a different product and do far less.

Blankets and duvets help a little and cause problems. A thick folded moving blanket over the roof absorbs some energy from small stones. It also soaks up water, grinds grit into the paint as the wind moves it, and departs entirely in a 60 mph gust, often dragging its straps across the paint on the way. If you use them, fold thick, cover the flat panels only, and weight them at the edges rather than tying them to mirrors.

Cardboard is close to useless. It has almost no impact absorption to begin with and turns to pulp in the first two minutes of rain, which is what always precedes the hail.

Floor mats work for exactly what they are: three or four small, dense rubber panels. Lay them rubber side up on the roof and bonnet and they will stop a handful of dents in the highest-value area. They do nothing for the other ninety per cent of the car, and they will blow off unless something heavy sits on them.

Bubble wrap, pool noodles, tarpaulins and yoga mats all behave the same way: some cushioning, no attachment, gone in the gust front. Tarpaulins are the worst of them, because a tarpaulin is a sail.

Whatever you use, never stand outside fitting it once hail has started. Nothing on the panel is worth a stone to the head.

• Works: a padded or inflatable hail cover, properly fitted and strapped.
• Helps a little: thick folded moving blankets, weighted at the edges, on flat panels only.
• Marginal: rubber floor mats on the roof and bonnet, held down.
• Useless: cardboard, once it is wet, which is immediately.
• Counterproductive: tarpaulins, loose sheets and anything that catches wind.

Because a roof over the car removes the problem, and a cover only softens it. Given the choice between fifteen minutes spent driving to a garage and fifteen minutes spent wrestling fabric in a rising wind, the drive wins almost every time.

The exception is timing. If the storm is already visible on the horizon and the garage is twelve minutes away through Friday traffic, you can find yourself under open sky in moving hail, which is the single worst place to be. That decision has to be made honestly, with the radar in front of you.

There is also a simple household version of this that most people skip: empty the garage. A great many Metroplex garages hold everything except a car. Two hours of clearing on a Saturday in February converts your most expensive weather exposure into a non-event for the rest of the year.

If you have two vehicles and one covered space, the newer car with the softer aluminium panels goes inside. Modern bonnets and boot lids dent at smaller stone sizes than the steel roofs they sit next to.

Move the car if a covered space is genuinely reachable, and if it is not, get the car facing the storm, get the soft protection onto the roof and bonnet, and get yourself inside. In that order.

Facing the car into the wind matters more than people expect. Windscreen glass is laminated and designed to take impacts; rear glass and side glass are tempered and shatter. Nose into the weather puts the strongest glass in the line of fire and shortens the exposed flat area of the roof.

Fold the mirrors, retract any aerial that retracts, and close the sunroof shade. If the car sits under a wall, park tight against the upwind side of it. If it sits in the open, get it away from anything that can fall on it.

Then stop. Being outside during large hail is a genuine injury risk, and the difference between a good and a perfect parking position is a few hundred dollars of repair that insurance is likely to be involved in anyway.

• Move it under cover if you can reach cover safely.
• Nose into the wind, mirrors folded.
• Weighted blankets or mats on roof and bonnet, edges secured.
• Everything loose in the yard put away, so it does not become a second impact.
• Go inside, away from windows, and leave the car alone until it is over.

Document the car properly, before you wash it and before you touch anything. Good documentation in the first hour is worth more than anything you can do later, because it ties the damage to a date and a storm while the evidence is still on the ground.

Wait until the storm has fully passed, then photograph in this order: one wide shot of the whole vehicle where it sat, the roof, the bonnet, the boot lid, then the tops of the wings and doors, then the glass, lamps and mirrors. Hail lands hardest on the horizontal panels, so those carry the case. Include the odometer and the VIN plate, and take a couple of shots with a coin or a key beside a dent for scale.

Light is everything. Flat morning or late afternoon light shows dents; direct midday sun hides them completely. If the damage happened in the evening, photograph again the next morning at a low angle along the panel rather than straight down at it.

Photograph the ground as well. Stones on the driveway beside a ruler or a coin establish the size that fell at your address, which is exactly the detail that gets asked about later. Keep any local news or weather report of that storm date.

Then check for anything that makes the car unsafe or lets water in: cracked windscreen, broken lamp lenses, a shattered rear window, a torn sunroof seal. That is the only part of this that is urgent. Cover broken glass and get the car under shelter if more weather is coming.

The step-by-step version of the following two days, including who to call and in what order, is set out on the after-a-hail-storm page.

Do not drive through active hail, and do not try to fix the dents yourself. Those two mistakes account for most of the avoidable damage we see after a storm.

Driving through hail multiplies impact speed. A stone falling at 60 mph hitting a car doing 60 mph into the storm arrives with far more energy than it would on a parked vehicle, and the windscreen takes it head on rather than the roof. If hail starts while you are driving, get off the road safely, ideally under a petrol station canopy or a bridge if you can pull fully clear of the carriageway, angle the car nose into the weather, and wait. Do not stop on the shoulder under an overpass in a way that blocks traffic; that causes crashes.

Do not push, pull or heat the dents out. Boiling water, hairdryers, plungers and suction cups either do nothing on a shallow hail dent or stretch the metal and crack the clear coat, which converts a paintless repair into a paint job. The same goes for the dry-ice videos. Paintless dent repair works from behind the panel with a light board and rods, and it depends on the paint being undisturbed.

Do not have the car washed at a brush wash before it is documented, and do not repaint or touch up anything before an inspection.

Do not sign anything handed to you at your front door in the week after a storm, and be careful with any crew that appears with out-of-state plates and a clipboard. That is worth its own page, and it has one.

Finally, do not assume small dents are not worth reporting. Hail damage reads as damage to every appraiser, buyer and lease inspector, whatever the physics of dimples might suggest.

Concentrated. The Metroplex takes most of its damaging hail in a narrow spring window, with a secondary risk that can reappear at almost any point in the warm season.

That concentration is useful, because it means the preparation on this page is seasonal work rather than a year-round habit. Clearing the garage in February, checking where your nearest public deck is, and putting the alert settings on your phone before the first warm front is most of the job.

Which months carry the risk, why the northern counties tend to fare worst, and what a bad season looks like against a normal one, are set out on the hail season page.