In 1743 Benjamin Franklin was getting pretty excited about the upcoming eclipse. It would be a lunar eclipse with the Earth's shadow casting itself across the bright full moon. Clear skies were a priority and so far things looked good on the day of the eclipse in Philadelphia. The skies were mostly clear and the wind brisk out of the northeast. Looking to the northeast horizon, Franklin saw nothing but clear sky with a lack of clouds being blown in by the wind.

To the northeast of him was his brother in Boston. Through a letter that arrived later that week, Franklin's brother reported clear skies on the day of the eclipse as well. As night approached, so did the clouds in Philadelphia. They were screaming in from the southwest horizon opposite the direction of the wind. How could this be? Sure enough, the overcast shut out the opportunity to view the eclipse and Franklin was disappointed. Meanwhile, his brother reported good visibility for the eclipse, with clouds rolling into the Boston area after the eclipse had ended. The Boston clouds had also streamed in from the southwest despite the northeast wind.

Franklin rejoiced in his brother's good fortune, but being the inquisitive type, he wanted to know how a northeast wind could bring in clouds from the opposite direction. In studying newspaper accounts of weather along the East Coast, Franklin was able to piece together the life-cycle of a storm that began in the southeastern United States and moved northeast up the coast. Surface-based weather observations showed the winds blowing opposite storm movement. Although Franklin didn't have the luxury of satellite and radar data or the large quantity of surface weather reports we have today, he was beginning to see the structure of a storm system. Weather needs to be looked at in a three dimensional view.

Winds at the surface rotate in a counter-clockwise direction around a low pressure center. As a low pressure center approaches from the southwest, we will feel northeast winds as they rotate in towards the center of the low. But the storm's motion is steered by winds aloft. The steering current winds, as they are appropriately called, blow at a level 10,000 to 15,000 feet above the ground. There was no way Franklin could detect those winds. He just felt the surface winds. A southwest upper air flow of winds would steer a storm center right up the eastern seaboard.

Another ingredient that aids the development of these storms is the warm water of the Gulf Stream. It is a fast moving warm current of Atlantic Ocean that transports warm water northward into the North Atlantic. The Gulf Stream waters brush by the east coast. When colder air off the continent interacts with this warmer water, low pressure centers may develop or become stronger. If the temperature contrast between continental cold air and warm Gulf Stream water is dramatic, storm systems can explosively increase in strength.

The huge blizzard that dumped several feet of snow on the Northeast U.S. earlier this month is an example of a powerful northeaster, or nor'easter. So called because they move northeast up the coast with strong northeast winds ahead of them, the nor'easters have been famous for creating huge storms with damaging winds, heavy rains and heavy snows.

People who live along the eastern seaboard of the United States are used to these storms. The prediction of these storms has improved with sophisticated numerical computer forecasts. But they can still be elusive storms for forecasters out east. The exact track of the low pressure center can determine where rain will fall as opposed to snow. This "rain/snow line" can wobble back and forth from east to west as the storm center meanders up the coast. Predicting that wobble is one of the most challenging forecast tasks in the world.

Even though Benjamin Franklin lost out on the chance to view an eclipse that his brother enjoyed, he was able to put the pieces of the puzzle together by going back and tracing the history of the storm. Even without the fancy weather equipment of today, Franklin showed that he was thinking way outside the box.