In 1743, Franklin planned to observe a lunar eclipse, but when he went outdoors at 8:30 he noticed that clouds had ruined his plans. Days later, he read that observers in Boston were able to see the eclipse, because clouds arrived just after the eclipse had ended.
The wind that night had been from the northeast, and the prevailing theory was that storms moved with the surface winds. So it should have been cloudy in Boston before Philadelphia, where he lived.
Through correspondence with his brother in Boston, he learned that storms often moved up the East Coast from southwest to northeast, and the winds within the storms did not necessarily dictate which direction they traveled. From this, Franklin became the first to accurately explain storm tracks in the colonies and how the winds behaved within those storms.
In 1755, Franklin observed a small tornado. As it passed, Franklin jumped on a horse and followed it. He observed dust being spewed about, but as it grew larger he saw leaves, then tree branches and tree trunks being tossed about.
Realizing the situation was becoming dangerous, he gave up his pursuit after three miles. He watched it pass through a field and become invisible as it dissipated. Thus, Franklin became the first recorded storm chaser in North America.
After the winter of 1783-84, Franklin wondered why the season had been so harsh. The answer, he speculated, was because of a large volcanic eruption in Iceland the previous summer. He suggested that the ash may have blocked vital sunlight in the northern hemisphere. This is another theory that has since been proved.
Finally, when Franklin first crossed the Atlantic, in 1724, he realized, after taking measurements on the journey, that some parts of the ocean were much warmer than others. Over the next 60 years, and seven more voyages, Franklin discovered and plotted the Gulf Stream.
He found that the Gulf Stream was like a river of warmer water flowing across the Atlantic. Thanks to his work, the travel time from America to England was reduced, because ships were able to make the trip in less time by following the Gulf Stream.