How Weather Helps Predict Flu Spread

The Weather Company’s Cold & Flu Tracker does a lot more than just signal that flu season has arrived. It quietly analyzes the atmosphere around you, helping to inform your decisions as you go about your day.

In doing a deep dive into the science behind this tracker, we spoke to Dennis O’Donnell, meteorologist and lead product manager at The Weather Company.

We learned that behind the simple risk meter (which can be found inside The Weather Channel app) is a sophisticated model that blends real-time weather patterns, forecasts, human behavior and health trends to calculate how likely illness is in your area.

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Behind The Scenes

Weather data, of course, plays a central role. The model incorporates current conditions and forecasts, like temperature, precipitation and humidity.

“We're using all of that information to understand where that virus is spreading and what actually causes that virus to spread,” explains O’Donnell.

(MORE: Your Home’s Humidity Could Be Helping The Flu Spread)

But flu risk isn’t static. It can shift rapidly, especially when the weather does.

A cold front may bring drier air, which can help viruses spread. But that same cold air combined with snow could temporarily reduce spread if schools close and people stay home.

“There’s nuance to all of this. There’s very rarely a one size fits all," O'Donnell adds.

But weather is only one piece of a much bigger puzzle. The model also accounts for sociological patterns: Are people inside? Was school canceled? Is there an upcoming holiday impacting travel?

The tracker focuses on “subcity” regions. These are areas bigger than a zip code but smaller than a county.

Using ILI (Influenza-Like Illness) data that accounts for how many people have gone to the doctor versus how many people actually have the illness, the model can help users understand where their illness risk is highest and avoid hotspots.

And because flu strains and human behavior evolve, the model must be reevaluated each year.

“The accuracy of a model always needs to be looked at continually,” O’Donnell says.

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The team compares its projections with state-level flu reports from the CDC. “At the end of the year we look at those reports and look at our model and see how it performed and we come together as a team to try and understand how we can improve the model.”

And even though the flu hasn't changed all that much in the last 100 years, O’Donnell notes that human interaction has.

“We can now go pick up our groceries and get groceries delivered. We can interact with people via Zoom or web meetings,” he says. “The spread has to be taken into account year to year just on how technology and how consumers and humans are changing.”

Using The Tracker In Real Life

O’Donnell emphasizes that the tracker is a decision-support tool.

"If flu is very high in my area, maybe I don't go out to dinner with my family," he suggests. "Avoid those closed spaces with a lot of people."

The tracker also encourages proactive planning.

“You want to get ahead of everything, so maybe you have a few more oranges, you eat a little bit more healthy,” O’Donnell says. “Maybe I go and buy that flu medication early so that I don’t need to run out later.”

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He compares it to checking the weather before you leave the house: “Am I going to need an umbrella today? Well, in this case, the umbrella is your cold and flu medicine.”

At its core, the flu tracker blends atmosphere and attitude, temperature and travel, humidity and holidays, into a daily snapshot of your health risk.

Weather is “a large contributor,” O’Donnell says, “but there’s so much that goes into how this happens.”

The goal isn’t to create anxiety. It’s to offer awareness.

“You really have to take into account your own level of risk,” he says. For some, it’s simply information. For others, it’s guidance that helps protect their health.

Either way, it’s about being prepared, just like checking the forecast before you step outside.

Weather.com lead editor Jenn Jordan explores how weather and climate weave through our daily lives, shape our routines and leave lasting impacts on our communities.