Ever checked a weather forecaster's website and seen it is expected to rain the next day, but then it turns out to mostly be sunny? WeatherWatch has explained why weather icons only tell half the story.
According to the forecaster, weather icons are used to "draw attention to what may be considered the main weather feature of the day". So while a thunderstorm may only last a quarter-of-an-hour, its icon may be used as it's considered the main feature of the day.
"This is a constant debate with weather forecasters vs which icon should go up."
WeatherWatch says the weather icon that is used on websites and mobile applications is often the key element of the forecast many people look at.
"But you need to read the 'fine print' in the surrounding/supporting weather maps and data to really get the forecast that is most accurate," it says.
"If this extra accuracy matters to you, or your business, then understanding and following the steps listed out below should help save you some frustration when the forecast doesn’t pan out the way you expected based mostly on that icon."
WeatherWatch uses this upcoming week as an example.
"This week a low-pressure zone in the Tasman Sea is falling apart – but will take until Christmas Eve to do so. This system is very weak, but the moisture and instability it brings will be triggered by the summer heat and that means the risk for heavy downpours and thunderstorms."
While in the morning this moisture may appear as drizzle or a brief shower, the afternoon heat will create sea breezes which push the moisture and warm air inland and into the atmosphere. This could trigger isolated but big downpours and thunderstorms.
"These then usually drift in one direction with the dominant sea breeze (and sea breezes in our two main islands can come in from all directions and converge/meet up inland somewhere)."
Depending on the size of these downpours and where the sea breeze pushes them, the daily thunderstorm or downpour risk area could be large. However, in reality, the storm could form in just one part of a region.
"Hence why you see the thunderstorm risk icon even though many days the more coastal centres (like Auckland and many other of our main centres) may be dry or sunny for much of the day."
Metservice provides a helpful explainer of what each of the icons it uses in its forecasts means. It also defines a number of terms it uses, such as "brief", meaning the weather event will only last for about an hour or less.
