Courtesy of TRIB LIVE|NEWS

By Megha Satyanarayana  Sunday, Aug. 31, 2014, 9:40 p.m.

Twice each day, a balloon floats over Western Pennsylvania, transmitting weather data to a building in Moon.

Inside that building, the offices of the National Weather Service, meteorologists combine the temperature and humidity data from the balloon with satellite feeds and computer models to release a weather forecast. Every three hours, they do it again. 

The region had a bitterly cold winter, then a mild summer. A few days ago, the Farmer's Almanac said another horrid winter was on the way. Could it possibly happen again?

“I tell people to focus on the warm, focus on the glass being half full,” said Fred McMullen, a meteorologist stationed in Moon. “Very rarely do we see back-to-back years of very heavy snowfall.” 

Very rarely. So, it's possible.

This is the crux of forecasting the weather, professional cloud-herders said. Every forecast is a probability, a chance, that something will happen. Long-term outlooks? Predictions in August about what will happen in December? All should be taken with a grain of salt, they said, and preferably, not the stuff road crews use.

“A month or two, or four, in advance? There is no ability with 100 percent certainty, or anything near 100 percent certainty, to make these forecasts,” said Jon Nese, a meteorologist at Penn State University. 

Which is why he doesn't put a lot of faith in almanac predictions. “No forecast is complete without some measure of probability,” Nese said.

Take a common phrase like a 50 percent chance of rain, said Paul Knight, the state climatologist of Pennsylvania. It doesn't mean there is a 50-50 chance of rain. It doesn't mean half a location will get rain and the other half won't.

“It means, if we look at 100 cases similar to today, in 50 percent of those cases, it rained. That pattern (of temperature, cloud cover, humidity and other data) produced rain,” Knight said.

Before weather balloons and fancy computer models, forecasting was all observational, he said. Atmospheric science was one of the first disciplines to adopt computing and then computer modeling. Modeling, especially as it is used in research, allows scientists to make changes in one variable, then see what happens to others. Raise the barometric pressure, he said, see what happens to precipitation. Change the wind speed, he said, and this is how the temperature changes.

“It gave us an opportunity as young budding scientists to say, ‘Oh, look! If we change this, look at that!' ” he said.

Models help to predict what happens, Knight said, which is weather. And they help to determine averages and patterns, he said, which is climate.

Climate is what meteorologists expect in a given region. Weather is the conditions that region experiences, Nese and Knight said.

The averages, Knight said, are going up.

“The normals have always been shifting,” Knight said. “It's just, of late, the normals have been shifting upwards.”

Some of the shift, other scientists say, is toward extremes, such as more hurricanes, bigger tornadoes, longer heat waves and perhaps, like last winter, longer cold spells.

In Allegheny County, spokeswoman Amie Downs said the Public Works Department monitors weather and seasonal predictions to decide how much salt to order. There are about 5,500 tons available. By early winter, 24,000 tons will be bought. After last winter, she said, road crews patched potholes, and more complicated road work will continue through October.

In rural areas, last year's winter is still rearing its ugly head. Jeff McKay, a weather geek, emergency management director and councilman in Monaca, said officials are already thinking about winter while trying to figure out road repairs.

“It seems like the roads took a big hit,” he said. “It's something we have to look at or it's going to catch up to us big.”

With fall about to befall us, and winter not too far away, what's the government's prognostication?

According to the Climate Prediction Center, it's an equivocal EC — equal chances of a normal winter, an above-normal winter or a below-normal winter.

Megha Satyanarayana is a staff writer forTrib Total Media. She can be reached at 412-320-7991 or megha@tribweb.com.