British weather decides whether a wash goes well. Tell the checker what you want to do and what it is like outside, and it says whether today is a good window, workable with care, or a day to wait. Every answer comes with the reason.
From your weather app or the car's dashboard.
No forecast to hand? Leaves rustling is light. Twigs moving all the time is gentle. Dust and loose paper lifting is moderate. Small trees swaying is fresh.
Pick yes after a Saharan dust fall or in heavy pollen.
The rules behind the checker
| Condition | Wash | Wax, sealant or polish | Why | Basis |
|---|---|---|---|---|
| Air at or below 0°C | Wait | Wait | Water freezes on the car, the ground and in seals. | Freezing point of water |
| Air above 0°C and up to 3°C | Care | Care | Surfaces can be colder than the air, so water can still freeze. | Met Office on ground frost. The 3°C line is our judgement |
| Direct sun on the car | Care | Wait | Water and product dry on the panel before you can rinse or buff. | Our own product directions say shade and cool panels |
| Moderate breeze, 13 to 18 mph | Care | Care for wax and sealant. Wait for polish | Wind at this strength raises dust and loose paper. | Beaufort scale, force 4 |
| Fresh breeze or more, 19 mph plus | Care | Wait | Foam and spray drift. Dust and leaves land on the panel. | Our judgement |
| Raining now | Care | Wait | You can wash and rinse, but nothing can be dried or applied. | Our judgement |
| Showers possible later | Fine | Care | Protection needs time before it gets wet. Polish needs a dry panel. | The product label |
| Dust, sand or pollen on the car | Care | Care | Grit dragged across paint scratches it. It has to be rinsed off first. | Our judgement |
The checker shows the most serious result. One Wait outweighs any number of good conditions.
Saharan dust: what it is and how to wash it off
- The Met Office describes Saharan dust as
a mixture of sand and dust from the Sahara
that can be carried as far as the UK when upper winds blow north. - It says this is
relatively common in the UK often happening several times a year
. - The dust needs rain to bring it down. Raindrops pick it up as they fall, and when they land and evaporate
they leave behind a layer of dust
. That is the orange film on the car the next morning.
It is fine mineral grit, so the one thing not to do is wipe it. This order gets it off without dragging it across the paint:
- Do not dry wipe, dust or use the wipers on a dry screen. Leave the car alone until you can wash it properly.
- Rinse from the top down. Let plenty of water carry the loose dust off before anything touches the paint.
- Foam and rinse again. A layer of No.02 Snow Foam left to dwell for a few minutes lifts what the rinse left behind. Rinse it off before it dries.
- Then wash by hand with two buckets, straight lines and light pressure, rinsing the mitt after every panel.
- Dry the car so the rinse water does not leave spots of its own.
- Rinse the door shuts, the fuel flap and the scuttle under the wipers. Dust collects there and runs back out later.
More detail is in our guides to using a foam cannon and the two bucket wash.
Frost and cold
- The Met Office explains that an air frost is when the air itself falls to freezing, measured at least a metre above the ground. A ground frost is ice on the ground or on objects whose surface is below freezing.
- It adds that
Ground frosts are common even when air temperatures are above 0°C
, and that a car can drop a few degrees below the air on a clear night. That is why there can be frost on the windscreen when the dashboard reads above zero. - For washing, that means a reading of 2 or 3 degrees is not a safe margin. Rinse water can freeze on the panel, in the locks and across the pavement.
- In a cold snap, wash in the middle of the day, dry the door seals, and keep run off away from where people walk.
- Road salt is the reason to keep washing through winter. Our guide to winter car care and road salt covers the routine.
Sun and heat
- Heat does its harm by drying things too fast. Rinse water dries into mineral rings, and shampoo, wheel cleaner or sealant that dries on the panel can leave marks.
- The air temperature is a poor guide, because a dark panel in direct sun runs far hotter than the air around it. That is why the checker asks about sun and not just degrees.
- The panel test: rest the back of your hand on the bonnet and the roof. If it feels warm, that panel is not ready. Move the car, wait for cloud or wash in the evening.
- When you have no shade, work one panel at a time: wet it, wash it, rinse it and move on, and dry the car the moment you finish.
- How bad the spots get depends on your water. The UK water hardness checker shows what yours leaves behind.
Wind
The Beaufort scale describes wind by what you can see it doing on land. These are the forces that matter for washing a car.
| Force | Name | Speed | What you see | For washing |
|---|---|---|---|---|
| 2 | Light breeze | 4 to 7 mph | Wind felt on the face. Leaves rustle. | Ideal |
| 3 | Gentle breeze | 8 to 12 mph | Leaves and small twigs in constant motion. | Fine. Panels dry a little faster |
| 4 | Moderate breeze | 13 to 18 mph | Raises dust and loose paper. Small branches move. | Care. Grit lands on wet paint |
| 5 | Fresh breeze | 19 to 24 mph | Small trees in leaf begin to sway. | Wash only, in shelter |
| 6 | Strong breeze | 25 to 31 mph | Large branches in motion. Umbrellas hard to use. | Leave it |
Rain
- Rain is soft water. It has not passed through rock, so it carries very little mineral and dries with far fewer marks than hard tap water.
- Washing in light rain is fine. Drying is not possible, so finish with a towel once it stops.
- Wax, sealant and polish are different. They need a dry panel, and protection needs time before it gets wet. That time is on the product label.
- A wet road undoes a wash faster than rain does. If the roads are filthy and you are about to drive, a rinse and foam may be all that is worth doing today.
Common questions
What is the best weather to wash a car?
A mild, overcast, still day. Cloud keeps the panels cool, little wind keeps dust off wet paint, and nothing dries before you can rinse and towel it.
Can I wash my car in freezing weather?
Not at or below 0°C, because the water freezes on the car and the ground. Just above freezing, surfaces can still be colder than the air, so wash in the middle of the day and dry the seals.
Is it bad to wash a car in direct sunlight?
It makes water spots and dried on product much more likely, because everything dries before you can rinse it. Use shade, or wash early or late in the day.
Is it OK to wash a car in the rain?
Yes. Rain is soft water and helps with rinsing. You cannot dry the car or apply wax or sealant until it stops.
How do I get Saharan dust off my car?
Do not wipe it. Rinse thoroughly, snow foam and rinse again, then wash by hand with two buckets and dry the car.
What time of day is best for washing a car?
Early morning or evening in warm weather, when the panels are cool. The middle of the day in cold weather, when frost is least likely.
Where the facts come from
- Frost: Met Office, what is frost and ice.
- Saharan dust: Met Office, what is Saharan dust.
- Wind: the land descriptions and speeds are from the Beaufort scale as published by the US National Weather Service.
- Everything marked as our judgement is exactly that. If you know of published testing that would improve a rule, send it to hello@soapx.co.uk.
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