Jason Samenow and Angela Fritz, both degreed meteorologists, run The Washington Post’s Capital Weather Gang blog, which provides weather commentary for the D.C. area as well as national and international weather coverage.
As we fearlessly — or fearfully — march toward winter’s peak, people inevitably turn to weather forecasts to try to anticipate when roads will be treacherous, whether offices and schools may be closed, and how much they’ll have to shovel from their driveways. But there are many misunderstood elements of weather and weather forecasting that can confuse people and undermine their ability to make everyday decisions. Better understand what weather information you can trust, as we tackle these five common myths.
1. Weather forecasters are usually wrong.
“I’m just telling you — if I did my job the way they do theirs, I’d be here about a week,” New England Patriots coach Bill Belichick said in October. “Based on the forecasts we’ve gotten so far this year, none of them have been close to what game conditions were. There was 100 percent chance of rain last week, and the only water I saw was on the Gatorade table. . . . They’re almost always wrong.”
Belichick’s comments were typical of the criticisms and jokes we hear about forecast accuracy. But while every meteorologist occasionally makes an errant forecast, weather predictions are generally quite good. In his 2012 essay “The Weatherman Is Not a Moron,” statistician Nate Silver pointed to weather forecasting as “the one area in which our predictions are making extraordinary progress.” A one-day temperature forecast is now typically accurate within about two to 2.5 degrees, according to National Weather Service data. In other words, when you see a forecast high of 82, most of the time the actual high will be between 80 and 85.
Forecasting rain is harder. And predicting the location and intensity of thunderstorms is like peering into a pot of boiling water and trying to figure out where a bubble will pop and how big it will be. Still, the most accurate forecasts — by the likes of AccuWeather, the National Weather Service and the Weather Channel — correctly predicted if there would be precipitation the next day 82 percent of the time in 2013, according to weather watchdog Forecast Advisor.
2. The polar vortex is a new, menacing weather phenomenon.
The polar vortex has generated a lot of hype this past year. When the term burst into the public lexicon last January, over-the-top headlines warned of “13 Things You Didn’t Know You Needed to Survive the Polar Vortex” and “Polar Vortex, Snow Storm Will Bring Certain Doom To D.C. Area Tomorrow.” Rush Limbaugh proclaimed that it was an invention of the left, part of an effort to manipulate the global warming debate. Poorly worded scientific explanations — such as one from City College of New York physicist Michio Kaku, who likened the vortex to a “tornado of cold air” — added to the alarm and confusion.
Rest assured, the vortex isn’t anything like a tornado. It isn’t a new phenomenon, either — it’s been referred to and studied by meteorologists for decades. The vortex simply describes a meandering circulation around the North (and South) Pole that typically contains the planet’s coldest air. Think of it as a fence holding in packs of dogs constantly trying to break through. When a dog sneaks through a weakness in the fence, that’s similar to a run-of-the-mill cold snap. But when a section of the fence collapses and you have a whole pack of dogs racing toward the U.S.-Canadian border, that’s analogous to our truly historic, punishing outbreaks of Arctic air. These happen a few times a decade, and such an event occurred last January.
3. Whenever the forecast calls for record lows, it undermines the case for global warming.
Every time there’s a cold snap, we see countless commentators on blogs and social media ridiculing the idea of global warming. If it’s cold, they reason, climate change must be a hoax. That seemed to be the thinking of Rep. Vicky Hartzler (R-Mo.) on Nov. 18, when the high at Reagan National Airport reached only 42 degrees. “Global warming strikes America! Brrrr!” Hartzler tweeted.
It’s frustrating how many times we have to repeat this, but climate change is measured by examining long-term trends in weather statistics over large areas, like hemispheres, or the entire planet, not events happening over a few days or even a few months in a small region. A fleeting cold wave or snowstorm over the eastern United States, for example, should never be used as evidence for or against climate change.
For the past several decades, Earth’s average winter temperature has warmed markedly, according to data from the National Oceanic and Atmospheric Administration and NASA. In fact, 2014 is on track to be Earth’s warmest year on record, according to NOAA. Residents of the eastern United States, where it’s been cooler than average much of the year, may find this strange. But it turns out that the region has recently occupied one of the lone cool pockets on an increasingly feverish planet.
4. It’s possible to accurately predict the weather weeks or months in advance.
The Old Farmer’s Almanac is forecasting that in the last week of January, rain in Washington will turn to snow, and that it will be sunny and cold afterward.
Yes, some people swear by these long-range forecasts. But in most cases, determining when it will rain or snow more than seven to 10 days into the future, and sometimes fewer, is simply beyond the range of predictability. And seasonal outlooks — such as whether it will be a cold, snowy winter — tend to be only marginally more accurate. Global weather patterns sometimes hint a few months in advance at how overall conditions will compare with average months. Often they don’t.
Big businesses such as Wal-Mart, Coca-Cola and JPMorgan Chase have bought into the promises of private forecasting services that use statistical models to develop year-ahead forecasts. WeatherTrends360 , for instance, offers day-specific forecasts for 11 months from now using what it calls a “secret sauce” technique. But we have never seen an independent, peer-reviewed analysis supporting the ability to provide a skillful forecast at such long ranges. By skillful, we mean that the forecast offers an improvement over simply looking at the average weather for a given location at a given time.
5. Local weather forecasters copy the National Weather Service.
The National Weather Service is a massive forecasting machine, with 122 offices that cover the entire United States, as well as Puerto Rico, American Samoa and Guam. One might easily assume that it’s the source of forecasts on local news outlets. However, many local meteorologists have impressive credentials and take great pride in their own hand-crafted forecasts.
Washington’s WUSA (Channel 9) meteorologist Erica Grow, who holds a BS in meteorology from Penn State University, combs global and regional weather models for the data that seeds her forecasts. She then tracks the models’ forecast data for each layer of the atmosphere until she can paint an accurate portrait of what the weather will be like, verifying the model data each day to tease out potential forecast bias. “This process can take an hour in the winter, but during calm patterns, I can zip through in 30 minutes,” Grow said.
Jacqui Jeras, a meteorologist for Washington’s WJLA (Channel 7) who has seals of approval from the American Meteorological Society and the National Weather Association, appreciates the challenge of producing a forecast every day. “While there is so much science involved in our jobs, there are still many unknowns,” she said. “So we get a chance every day to start fresh and give people a correct and accurate forecast.”
At the Capital Weather Gang, we use a team-oriented approach in which each forecast builds on the previous one, with the goal of homing in on the highest accuracy. Before high-impact weather events such as snowstorms, we often hold lengthy discussions involving multiple meteorologists. We believe a consensus forecast is often more accurate than a forecast by any one individual.