Watch, Warning or Just Weather? A UMD Meteorologist Decodes Alerts on Your Phone

UMD lightning researcher and former National Weather Service forecaster Joseph Patton breaks down hazardous weather alerts and what they mean. 

Before University of Maryland faculty specialist Joseph Patton studied lightning and extreme weather from space, he learned about storms the hard way—growing up in Baton Rouge, Louisiana, through infamous hurricanes like Katrina, Gustav, Rita and Isaac. He went on to forecast weather for the National Weather Service in western Kansas, where blizzards, tornadoes and dust storms were a regular part of the job.

Moving eastward hasn’t made the weather any less interesting for Patton. 

“Maryland sits in a weird little place for weather,” Patton said. “We’ve got mountains right to our west, and then we’ve got the hot ocean with the Gulf Stream right to our east. It’s like an atmospheric mixing bowl for ingredients for crazy weather.”

Now, as a meteorologist and lightning researcher for UMD’s Cooperative Institute for Satellite Earth System Studies, Patton uses a satellite instrument called the Geostationary Lightning Mapper (GLM) to help forecasters issue faster, more accurate warnings. He monitors lightning across the continent, tracking storms, tornadoes and even wildfires sparked by lightning strikes. 

In an interview with the College of Computer, Mathematical, and Natural Sciences, Patton explained what Maryland’s emergency alerts actually mean—and what you should do when one buzzes on your phone.

This interview has been edited for length and clarity.

Most people hear about weather warnings through their phones. How does that work? 

You don’t need a special app. The alerts come through a federal system called Wireless Emergency Alerts, or WEA, and they’re based on whichever cell tower your phone is connected to at that moment. So, if you commute to campus, you’ll get alerts for wherever you happen to be as you travel—including the area you're coming from.

I'd recommend everyone check that those alerts are turned on. You can't pick individual hazards—there's no toggle for "tornado" or "severe thunderstorm." What you can control are the broader categories, and the two that matter for weather are "Extreme threats" and "Severe threats." With both of those enabled, you should get everything important: tornado and severe thunderstorm warnings in the late summer months, and blizzard or ice storm warnings once the weather turns cold. The federal government also runs a plain-language explainer on the program at ready.gov/alerts.

What’s the difference between a watch and a warning?

The National Weather Service issues a watch when forecasters are anticipating hazardous weather sometime in the next few hours to few days. Think of it as roughly a coin flip—the confidence is lower, and the area is big. A watch is usually drawn as a rectangle a few hundred miles (several hundred kilometers) across, about the size of a state or two in this part of the country. It's saying the weather might happen somewhere in here, soon.

A warning is much more specific. It means dangerous weather is already occurring, or forecasters are confident it's about to, in a much smaller area—on the order of tens of miles across, about the size of a county or a large city.

The timing shifts depending on the hazard. A tornado watch might come only a few hours before storms fire, while a blizzard watch can go out two or three days ahead.

The simplest way to think about it: a watch means be prepared and stay informed. A warning means take action and seek shelter. If a tornado watch is issued, that's when I'd bring in anything fragile from outside and make sure I know where my nearest shelter is. When the warning comes, you're moving fast—and you're glad you did that prep earlier in the day. That framework applies across nearly every hazard the region faces, from severe thunderstorms to blizzards to excessive heat.

We get a lot of flash flood warnings here in Maryland, especially in College Park. What should people do?

In this area, it's usually urban flooding—a lot of rainfall over a lot of concrete that can't be absorbed, especially when multiple storms cross the same area in a few hours. 

If you're driving and you see water covering the road and can't tell how deep it is, the road underneath may even be washed out. The NWS has a slogan for this, and they've been saying it for decades: turn around, don't drown. 

If you're in a building, stay above the basement level and don't wait until the water is at your doorstep to seek higher ground.

Maryland’s ongoing drought is also making the flooding worse. Much of the state, including Prince George’s County, is abnormally dry, according to the U.S. Drought Monitor—and dry soil absorbs rain more slowly. If you’ve ever watered a plant that has dry soil, you’ll know what I’m talking about.

We’re in hurricane season now. Should Maryland residents worry about tropical storms?

The Chesapeake Bay area gets a tropical system like a hurricane roughly once every decade or so, so it’s something the university has to be prepared for. The good news is that you usually get to know a few days ahead of time because the National Hurricane Center issues forecasts up to seven days in advance. 

Growing up in South Louisiana, hurricanes were something I experienced multiple times a year. For Maryland, most likely it's just going to be really rainy and rather windy for a day or two. We may occasionally experience tropical weather systems, but it’s rare to get direct landfalls by full-strength hurricanes. The best thing to do is make sure you have spare batteries and flashlights in case the power goes out and then hunker down and wait it out. 

What about winter weather? What should we expect this winter? 

A winter weather advisory means a few inches of snow—usually not a big deal. A winter storm watch or warning means significant snow or ice, typically six inches or more, when driving gets difficult and power lines can come down. The exact criteria vary by location, depending on how prepared a place is: five inches in New York City might not warrant a winter storm warning, while five inches in Atlanta almost certainly would. A blizzard warning means whiteout conditions. You could get lost in your own front yard, and that happens all the time. Don't go out if you absolutely don't have to.

2026 is a big El Niño year. El Niño is basically a measure of how anomalously warm or cold the waters of the central Pacific Ocean are. Right now, those surface waters are a lot warmer than average.

In a typical winter El Niño pattern, we see cooler and wetter conditions creep up into the eastern seaboard. I would expect a slightly higher likelihood of higher snowfall this winter. But that's just an average—there are certainly El Niño years where we had less than average snowfall. I think it's more likely we'll have higher snowfall than the half inch we got in 2023.

How does your work with the Geostationary Lightning Mapper (GLM) influence our weather alerts?

The GLM sees the entire spatial footprint of a lightning strike—all those complex branches—not just the point where it hit the ground. One example you may see on campus is Maryland football home games. They'll delay the game if there's a lightning strike within a certain radius of the stadium. Even if the lightning only hit the ground 10 miles away, the mapper can see that part of that flash was only five miles from the stadium—so that area is more susceptible to a subsequent strike than they thought. 

Even a weak thunderstorm can create cloud-to-ground lightning strikes which could be deadly. About 15 to 20 people still die every year in the United States from strikes, and they're usually doing something ordinary outdoors—mowing the lawn, walking to the car, standing on a field. That number has actually dropped significantly. In the '50s and '60s it was closer to 100 per year and part of that is because places like sports stadiums are taking lightning more seriously. 

What kinds of weather trends can we expect here in the next few years? Is weather getting more extreme? 

There are a lot of indicators—such as increasing global atmospheric temperatures and humidity over the Plains—that would suggest damaging windstorms are going to be more likely in the future. College Park saw one in 2012, a type of storm called a derecho: a fast-moving line of thunderstorms that produces destructive straight-line winds over hundreds of miles. We've actually seen a shift in where we'd expect the most severe weather to happen. You may have heard the term Tornado Alley—that's been from northern Texas into Oklahoma and Kansas, and it's started to shift a little bit eastward, into what some people call the Mid-South: Arkansas, Tennessee and Kentucky.

That doesn't mean Tornado Alley is coming to D.C. This area already gets plenty of tornadoes and may well see more as patterns change, but I don't expect it to become part of the Alley. Forecasting is a little like baking a cake. You can have all the right ingredients and all the right instructions, but if things don't happen in a certain order, or you use too much baking powder, it's not going to come out right. The ingredients for severe weather are there and appear to be increasing. Whether that means a specific place sees a specific hazard more often in a specific window is really hard to say.

You used to issue weather alerts yourself. What do you tell people who say storms come without warning?

Forecasting is hard, and I understand the frustration. It's a delicate balance between warning early enough to give people time, but not so early that you warn about something that never becomes severe. That's what I stress to forecasters when I teach them to use the lightning data we now get from the GLM: if the weather's already happening, it's not much of a warning. You have to give people some amount of time to react, prepare and keep themselves safe.