What a difference a week makes.

Barely a week ago, North Georgia was dealing with 2-3 inches of snow and near-freezing temperatures. On Wednesday, with temperatures in the low 60s, a thunderstorm rumbled through.

It’s a sign spring is — finally — on the way, say forecasters at the National Weather Service.

But Wednesday’s thunder could be a harbinger of a stormy spring.

“You’ll see above average precipitation (in the Southeast),” said Jon Gottschalck, head of forecast operations for the weather service’s Climate Prediction Center in Maryland. “Thanks to strong upper-level jet streams continuing to bring cold Arctic air down to mix with warm Gulf air, you’ll also see an enhanced likelihood of severe weather.”

Today’s forecast calls for showers and possibly a thunderstorm. Another inch of rain is possible on top of the 2 inches that fell Wednesday, said Mike Leary, a forecaster at the weather service’s Peachtree City office.

A flood watch is in effect for most of North Georgia through midmorning today.

Leary said there is a slight chance that thunderstorms today, tonight and Friday could be severe.

“It’s something to watch out for,” he said. “The chances will diminish going into the weekend.”

The rainfall has helped Lake Lanier maintain its level. At 8 p.m. Wednesday, the lake was at 1,070.69 feet, nearly two-thirds of a foot above the level the U.S. Army Corps of Engineers hopes to maintain in the winter.

Leary said rain remains possible through Sunday night.

It’s not surprising that severe weather is possible. March is the official beginning of tornado season in Georgia, and Georgia Emergency Management Agency officials are already urging residents to pay attention to weather reports during the spring.

Georgia is one of the top-five states for tornado activity, GEMA said. In 2009, more than 50 tornadoes touched down in Georgia. In 2008, four tornadoes touched down in Hall County in one afternoon.

Gottschalck said the El Niño weather pattern is responsible for part of the heightened severe weather threat. But he also blamed Arctic Oscillation, a phenomenon that pushes cold Arctic air much farther south than usual.

El Niño is a seasonal weather pattern in which warm Pacific winds periodically strike the West Coast and push moist air to the nation’s interior. El Niño causes droughts in some areas, while causing floods in others.

In an El Niño season, Gottschalck said, temperatures in the Southeast are usually colder than normal and rainfall amounts are higher.

The coupling of the Arctic Oscillation with El Niño “created the perfect storm for snow lovers,” he said. “You had above normal moisture and below-normal temperatures.”

It also will increase the risk of severe weather this spring, he said. Cooler than normal air will continue to barrel down on the South for at least another couple of months. When it mixes with the warm, moist air from the Gulf of Mexico, the result is thunderstorms.

“The storms will certainly intensify in April and into May,” Leary said. “We can have storms all the way through the summer, but they’ll be most intense this spring.”

El Niño is expected to weaken this summer, Gottschalck said, and that means a return to more normal weather patterns across much of the South.

While the Southeast might see more tornadic activity this spring, the hurricane season later this year could be milder than normal, Gottschalck said. The weather service’s official hurricane prediction for this year won’t be released until May.