4 Common Mistakes People Make Using Weather Apps

I took my seat at the University of Georgia – University of Oregon football game this weekend, and the person seated to the left of me initiated small talk. After learning that I was the director of the Atmospheric Sciences Program at the University of Georgia and a meteorologist, she said, “Maybe you can tell me why the forecast was so wrong today, my App said….” It was an innocent question, but one that I (and many of my colleagues) are intimately familiar with. Because it wasn’t raining at the stadium, she felt the forecast was wrong. Here are four mistakes that I often hear about when people consume information from Weather Apps.

The first mistake is the long-standing misunderstanding of “percent chance of rain.” The National Weather Service – Atlanta explains a 40 percent chance of rain this way on its website – “The “Probability of Precipitation” (PoP) simply describes the probability that the forecast grid/point in question will receive at least 0.01 inches of rain. So, in this example, there is a 40 percent probability for at least 0.01 inches of rain at the specific forecast point of interest!” More specifically, the National Weather Service website goes on to explain, “(1) If the forecaster was 80% certain that rain would develop but only expected to cover 50% of the forecast area, then the forecast would read “a 40% chance of rain” for any given location. (2) If the forecaster expected a widespread area of precipitation with 100% coverage to approach, but he/she was only 40% certain that it would reach the forecast area, this would, as well, result in a “40% chance of rain” at any given location in the forecast area.” The PoP is calculated by multiplying the weather forecaster’s certainty (C) that precipitation will occur (form or move int the area) by areal coverage (A) expected. An adjustment factor is made by shifting the decimal point two places to the left.

The second mistake that many people tend to make with Apps is related to duration. There seems to be an assumption, as one colleague noted on my social media page, that an 80% chance of rain translates in the minds of many people that it is going to rain “all day.” If you consume the definition properly, the 0.01 inches of rainfall might happen early in the morning, over the course of a few hours, or later in the evening. A third mistake, related to the first two, is the assumption that the forecast is the same for every single place in the area. On typical summer days around here, it can be sunny at my house and raining at my son’s school a few miles away. The combination of probability, evolving weather, and how it is distributed across an area is difficult to synthesize into an icon on our smart watch or phone.

The final mistake is related to evolving weather itself. Many people look at their Weather App icon, and it might have a sunny icon or a rainy cloud with a lightning flash. However, that static representation of the weather is not suitable for dynamically-evolving weather situations, particularly severe weather. It is important, in dangerous weather situations, to understand the evolving threat. One strength of many Apps is the weather radar. They are useful for identifying precipitation or storm location and evolution. Many of them even have lightning flash locaters too. I also highly recommend that your Wireless Emergency Alerts are activated during severe weather or that you have a weather alert App enabled.

Look, I am a meteorologist. I can assess weather for myself using various tools. However, I do have a couple of Weather Apps on my phone. I am not anti-Weather App. This short essay is intended to caution you about how to use them and to not trash the forecast because you didn’t understand how to consume the information presented to you. At the end of the day, the weather information from your App is not coming from the “App Fairy.” It is based on weather observations, numerical weather models, and professional analysis. It is also incumbent that weather information providers move beyond the “inertia of practice.” In other words, we have a lot of jargon and terms of practice in the weather enterprise that are absolutely meaningless to the general population. Know your audience.