Australia Weather News

It has been a frosty start to winter, but for many areas of Australia, the lower temperatures are coinciding with faster drying clothes.

This sounds like a fallacy since drying relies on evaporation, and the warmer it is the faster moisture in your clothes converts to a gas and escapes.

For southern and central Australia, drying is generally — but not always — faster in summer.

However, the difference is often minimal across eastern states and conditions this week in coastal regions like Sydney and Brisbane, despite cold temperatures, have been optimal for washing productivity.

So how can laundry times be shorter when the weather is cooler?

The answer can be found in the details of the drying process.

Firstly, while higher temperatures lead to faster evaporation, even in air below freezing, some molecules of water can still break free and convert into a gas.

However, what is critical for efficient drying is not just evaporation, but more specifically the rate of evaporation (moisture leaving your clothes) relative to the rate of condensation (moisture arriving on your clothes).

Washing is a dry breeze

Despite the intuition that your laundry will dry faster in hot weather, surprisingly, science tells us the air temperature is the least important variable in determining drying times.

The two most important factors are fairly obvious — that it is not raining and the sun is shining.

Direct sunlight supplies far more energy compared to what is emitted from the ground or the air, which is why bitumen and car seatbelt buckles get so hot.

The next three factors, in order of importance, account for remaining day-to-day drying variability?

From this hierarchy, humidity is more important than wind and temperature, and that is because the moisture in your clothes has to evaporate into the air — and the process is far more efficient when humidity is low.

If the surrounding air is saturated with moisture (high humidity), condensation back onto your clothes will negate evaporation.

This is the same reason why it feels hotter when it is humid, as evaporation of your sweat is restricted and therefore less cooling occurs through the absorption of latent heat.

Next comes wind. On a still day, a slim layer of air around your clothes will become humid due to the evaporation, which reverts us to the saturated air-drying issue.

On a windy day, though, the water vapour from your laundry is blown away and continuously replaced by unsaturated air. This is why hair dryers have a fan.

And finally, the last and the least variable is temperature, which also affects drying times but to a lesser degree than wind and humidity.

Based on the above, let's compare drying times between a typical humid, summer day and the wintry, dry weather seen this week along parts of the east coast.

The results, calculated from an online calculator based off a thick garment with 4-millimetre fabric thickness, revealed a considerable improvement in drying under the cool scenario — even with only a 5 -kilometre-per-hour increase in the wind speed.

So what comes out in the wash is do not let the winter cold stop you from hanging out your washing — just time your laundry to coincide with days of lower humidity and sufficient wind.