"The flash of light you saw was not a UFO. Swamp gas from a weather balloon was trapped in a thermal pocket and reflected the light from Venus." (Agent K, Men in Black)
Weather balloons are infamous in popular culture, but not for their weather monitoring purposes. Thanks largely to the 1947 Roswell incident, they've become objects of UFO sighting claims and cover-ups. The fact that weather balloons are high-traveling devices with a spherical/cylindrical shape probably doesn't help either.
NOAA's National Weather Service launches weather balloons everyday, twice daily. Balloons travel from Earth's surface up to a height of 20 miles and are responsible for collecting air pressure, temperature, humidity, and wind data at different levels of the atmosphere. After a balloon reaches an approximate altitude of 100,000 ft, it pops and falls to the ground--sometimes as far as several hundred miles away from it's launch location.
In an attempt to make debris from these instruments less mysterious, NOAA now labels its balloons with the words "Harmless Weather Instrument."
With their smooth lens shape and stationary movement, lenticular clouds are frequently likened to UFOs.
A member of the altocumulus family of clouds, a lenticular forms at high altitudes when moist air flows over a mountain peak or range resulting in an atmospheric wave. As air is forced upward along the mountain slope, it cools, condenses, and forms a cloud at the wave's crest. As the air descends the mountain's opposite side, it evaporates and the cloud dissipates at the wave's trough. The result is a saucer-like cloud which can "hover" over the same location for as long as this airflow setup exists--up to days at a time!
The first lenticular to be photographed was seen over Mt. Rainier in Washington state.
Less than 10% of the U.S. population has reportedly witnessed ball lightning--a free-floating red, orange, or yellow sphere of light. According to eye witness accounts, ball lightning can either descend out of the sky or form several meters above ground. Reports differ when describing its behavior; some mention it acts as a fireball, burning through objects, while others refer to it as a light that simply passes through and/or bounces off of objects. Seconds after forming, it is said to either silently or violently extinguish, leaving the smell of sulfur behind.
While it is known that ball lightning is related to thunderstorm activity and usually forms simultaneously with a cloud-to-ground lightning strike, little else is known as to the reason for its occurrence. It remains rare and largely undocumented.
St. Elmo's Fire
Another atmospheric event with other-worldly characteristics is what's referred to as St. Elmo's fire. Described as a fluorescent bluish-white orb of light that "sits" at the end of a conducting structure (such as a lightning rod, spire, mast, or airplane wing), this phenomena has an eerie, almost ghost-like appearance.
In reality, St. Elmo's fire is actually a coronal discharge caused by an extreme imbalance in electrical charge generated during electrical storms (thunderstorms, volcanic ash clouds, etc.).
The occurrence takes its name from Saint Erasmus (the patron saint of sailors) because it was often seen on the mastheads of seafaring ships.