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Clearing up the ‘patchy rain’: introducing a more precise forecast language

Clearing up the ‘patchy rain’: introducing a more precise forecast language

You probably read or hear the weather forecast almost every day, but what do all those terms actually mean? To make rain forecasts more helpful, the Bureau is changing the terms used in its forecasts.

How many times have you read or heard on the radio that there’ll be scattered showers or patchy rain where you live or work? How much does this information really help you—especially if you’re about to hang out the washing, or are trying to decide whether to take an umbrella to the office?

As the Bureau’s weather information becomes more detailed and precise, we want the language of our forecasts to follow suit. People have told us that ambiguous terms such as patchy, isolated, scattered or widespread often lead to confusion, and that they just want to know how likely it is to rain, and how heavy the rain will be if it does.

Example of the current style forecast

So we’re changing the way we describe the likelihood of rain, to ensure that our forecast descriptions are every bit as clear and precise as our graphical services.

Forecasts now tell you if the chance of rain in your area is slight, medium, high or very high at different times of the day, with a percentage equivalent.

Let’s explore the changes in more detail by looking at a new forecast for Perth and the surrounding area.

Example of the new style forecast

The left side of the forecast provides the temperatures, chance of any rain, and possible rainfall amounts for Perth’s city centre.

The right side elaborates on these figures with a statement such as a ‘High (70%) chance of showers in the morning’. Sounds like umbrella weather, doesn’t it?

Let’s explore this a bit further. ‘High’ relates to a simple scale of how likely you are to receive rainfall in that forecast area. This scale is shown in the table below:

Chance of rain

Terminology used

0%, 10%

No mention of rainfall in forecast.

20%, 30%

Slight (20%) chance of… Slight (30%) chance of…

40%, 50%, 60%

Medium (40%) chance of… Medium (50%) chance of…

Medium (60%) chance of…

70%, 80%

High (70%) chance of… High (80%) chance of…

90%, 100%

Very high (90%) chance of… Very high (near 100%) chance of…

This simple information is probably enough to tell you how likely you are to get wet and whether you need a raincoat. But what else can you tell from the forecast?

Timing of rainfall: If the chance of rain is confined to a short period of the day, you may see words such as ‘most likely in the morning’. In this example we only expect showers in the morning.

Heavy rainfall: If very heavy rainfall is a possibility, you may see words such as ‘Showers, heavy at times’. This one might be a useful warning to check that those gutters are clear.

Thunderstorms: If there is a chance of thunderstorms during the day, this will be mentioned.

Other weather: When appropriate you will also be advised of other weather phenomena, such as hail, frost, fog or snow.

So there you have it. These simple changes to your forecast terminology will help you make important decisions about your outdoor activities every day.

More information:

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