By the time you read this you’ll know whether the stronger, faster computers of today are any better at predicting severe storms than the weather balloons and pen on paper used in the old days.
The same advanced computer software and satellite images that had been tracking this storm’s movement since it churned off the coast of Los Angeles late last week predicted the worst of it would hit Chicago early Wednesday morning. The brunt of the massive storm sweeping in from the south was expected to bring 60-mph winds and water surges by the lake and dump up to 2 feet of snow in parts of the city.
If you’re among those who said, “I’ll believe it when I see it,” you’re in good company.
Predicting the unpredictable nature of severe storms has always been a bit of a guessing game. On January 26, 1967, the forecast was for 4 inches of snow in Chicago. The city got 23 inches. On January 13, 1979, the forecast again was for 4 inches, but 18.8 inches of snow fell. On January 1, 1999, the forecast was for 6 inches of snow, but the city got 21.6 inches.
Even in this age of supercomputers and satellites, the best scientific predictions come with some level of uncertainty. But experts said new computer models that factor in the inherent unpredictability of these storms bring meteorologists closer than they’ve ever been to a sure thing.
“Today the technology has improved so that we get a really good idea of the magnitude of what is about to occur,” said Richard Castro, a meteorologist at the National Weather Service in Chicago.
Castro’s computer models predicted an 85 percent chance that Chicago would see at least 8 inches of snow between Tuesday and Wednesday. The odds that the city would see a foot or more were about 75 percent.
A far cry from when meteorologists simply charted rudimentary weather balloon data on a map to gauge the course of the storm, today’s weather service computers constantly process atmospheric profiles of temperatures, moisture and winds taken throughout the country by surface observation, weather balloons, satellites, commercial airlines and advanced weather instrumentation on weather service aircraft.
Computer modeling also has improved, now taking the mean of up to 20 different computer-generated scenarios of a storm’s impact, said John Ferree, a severe storm expert at the National Weather Service in Oklahoma. By factoring in uncertainties about how a storm will behave, these models are a vast improvement over the days when computers simply ran one scenario and left the rest up to chance, experts said.
As a result, this “ensemble” method of computer modeling that was not widely used even five years ago has quickly become a critical tool in the science of weather forecasting.
“What they’re doing is they’re getting different equations into the model to solve the question about what the weather will be like in a lot of different ways,” Ferree said.
Though computers were used in 1967 and 1979 in weather forecasting, they were comparatively slow and anemic, able to handle very little data input compared with today’s computers, Castro said. Thus they failed in seeing the coming big storms in 1967 and 1979. By 1999, computing power and inputs had improved. The city knew two days ahead of time it was facing a major storm — though not that it was about to get the second-largest snowstorm in the city’s history.
In contrast, scientists could tell as early as Friday that a major storm forming in the Pacific Ocean off California could have Chicago in its sights. Fueled by moisture in the Pacific and the Gulf of Mexico, the storm moved east, bringing rain throughout the southwest and freezing rain and snow to parts of Texas and Oklahoma on its trek toward the Great Lakes.
Gilbert Sebentse, a staff meteorologist at Northern Illinois University, said a storm like the one pounding Chicago this week could not have been predicted 20 years ago, much less in the 1960s and 1970s.
In the late 1990s, the Federal Aviation Administration and local municipalities wanting more weather information began installing hundreds of automated weather reporting stations throughout the country, Sebentse said, measuring and reporting local weather conditions 24 hours a day. That data is now automatically sent to two national weather hubs that make it available to the National Weather Service and online.
“We knew this blizzard was coming three days before it even developed,” Sebentse said. “There are still things we don’t understand, like how to pinpoint snowfall down to the last inch, but we knew this storm system could produce a foot of snow or more three days ago. That still amazes me.”
