Car wash FAQ

A 0–100 score computed from your local weather forecast. It weighs rain probability now and over the next 6 hours, actual precipitation, temperature, humidity, wind gusts, and (where air-quality data exists) airborne dust and six pollen species. 70+ = WASH, 45–69 = BORDERLINE, under 45 = WAIT. The full penalty table is published on the method section.

When rain probability stays under 20% for the next six hours, humidity is 40–70%, winds are gentle, and temperature is between about 5 and 28 °C (41–82 °F). Early morning or late afternoon beats midday, when direct sun flash-dries water into mineral spots. The index finds these slots for you as 2-hour wash windows.

Generally no. Rain re-deposits road film and dust onto clean paint and usually dries into spots. If rain probability exceeds about 30% within the next 6 hours, waiting is the better spend — the index counts how many dry days a wash would actually hold before the sky undoes it. One exception: a quick pre-rinse before heavy rain can float loose grit off so it doesn't get ground into the paint.

Above 5 °C (41 °F), yes — just dry seals and locks well. At or below freezing, no: water wicks into door seals, locks and trim and freezes them shut, wash chemicals underperform, and ice can form on panels before you finish drying. The index treats freezing as an automatic WAIT.

Above roughly 32 °C (90 °F), water and soap flash-dry on the panels before you can rinse, leaving streaks and mineral spots. If you must: shade, panel by panel, early morning or evening, and keep every surface wet until the final rinse.

Early morning or late afternoon. Midday sun heats the panels and bakes soap residue in. Morning usually also brings the day's calmest wind — less airborne dust landing on wet paint.

Every two weeks is a solid baseline. Go more often during pollen season, after winter road salt, near coastal salt air, or when bird droppings and tree sap show up — all of them etch clear coat if left sitting.

Rinse first, always. Flood the pollen off with water before anything touches the paint — dry-wiping drags abrasive grains across the clear coat. Then a normal two-bucket wash. During peak pollen weeks, frequent quick rinses beat occasional deep washes.

When rain is likely within 6 hours, at freezing temperatures, during peak pollen or dust events, in strong gusty wind (blown grit sticks to wet paint), or in direct midday summer sun. Every one of these is a penalty in the index — stack a couple and the verdict goes WAIT.

The tool pulls 7 days of hourly forecast for your location from Open-Meteo (plus air quality where available), scores every hour from 100 down using the published penalty table, then reports the verdict for right now, your best 2-hour window today and tomorrow, a 7-day outlook, and how many dry days a wash would hold. Nothing is hand-tuned per user; everyone gets the same honest math.

As accurate as modern weather models: very good inside 24 hours, decent to about 3 days, indicative beyond. The confidence figure next to each verdict reflects how steady the next six hours of forecast look — a twitchy forecast earns less trust.

Mostly, yes. Spots are minerals left behind when water evaporates faster than you dry. Shade, panel temperature below ~28 °C, moderate humidity, and prompt microfiber drying prevent most of them — which is exactly why the index penalises heat and hunts the calm windows.