How accurate are weather forecasts?
Posted April 25, 2021 7:06 a.m. EDT
Updated April 25, 2021 10:15 a.m. EDT
Raleigh, N.C. — When you think of your local meteorologist, no matter who that person may be or where they may work, your next thought may often be “it must be nice to be wrong half of the time and still get paid.”
However, the statistics show local meteorologists are far more accurate than you may think.
Here in Raleigh, meteorologists use weather sensors at Raleigh-Durham International Airport as a baseline for determining whether their forecasts are accurate or inaccurate. Why Raleigh-Durham International Airport?
RDU is a climatological site with daily records dating back to 1944. That data is used to derive our climate “normals,” including daily, monthly and seasonal temperatures and precipitation.
While that may seem unhelpful regarding what weather you will see where you live, meteorologists in our area take it one step further and send individual forecasts to an independent company where they verify the accuracy of the forecast over our larger area from the North Carolina/Virginia border to the Sandhills and from the Piedmont through the Coastal Plain.
Weather conditions like temperatures, cloud coverage, precipitation type and timing and whether we will see severe storms are just some of the criteria used to determine the accuracy of the forecast.
When it comes to forecast accuracy, data from the National Weather Service suggests a one-day temperature forecast is typically accurate within about 2 to 2.5 degrees. In other words, when you see a forecast high of 80, most of the time the actual high will be between 78 and 83.
Longer-range forecasts are less accurate. Data from the National Oceanic and Atmospheric Administration suggests a seven-day forecast can accurately predict the weather about 80 percent of the time, and a five-day forecast can accurately predict the weather approximately 90 percent of the time. However, beyond 10 days, a forecast is only right about half the time.
Beyond the numbers, the perception of the weather will never accurately match the reality of the weather. This is because forecast parameters include a good amount of probability and chance.
For instance, meteorologists use percentages to describe the chance of precipitation occurring at any point you select in the area. Mathematically, the percentage comes from the confidence that precipitation will occur somewhere in the forecast area multiplied by the percent of the area that will receive measurable precipitation.
Today, we often can be 100 percent confident that precipitation will occur somewhere in the forecast area. How much of that area will be covered by rain at a single time is the factor constantly changing and harder to determine. Probability is ultimately why the forecast is perceived to be accurate or inaccurate.
So how does your local meteorologist’s forecast differ from an app-based forecast provided on your phone? Meteorologists use a blend of weather models and experience to analyze trends within those models. Many of the app-based forecasts use a single weather model. More often than not, meteorologists’ collective forecasts are far more accurate than any one model.
No perfect weather model exists, and it takes a qualified meteorologist to discern nuances and biases within each model to determine the most accurate solution and forecast.
While the forecast may not always be perfect, forecast accuracy is a lot higher than many people are willing to admit. So the next time you’re thinking “it must be nice to be wrong half of the time and still get paid,” remember that the forecast may have been wrong for your neighborhood but correct for one right down the street.