March 30 (UPI) -- The last blue moon until 2020 will peak in the sky at 8:37 a.m. EDT Saturday.
For the second time this year, a blue moon will appear. The first was in January.
Linda Lam, a Weather.com meteorologist, said people living in the South, Southwest and West Coast of the United States have the best chance of seeing the blue moon, but a cold front may block the view along much of the East Coast.
The full moon is called a blue moon when it shows up for the second time in the same month. Contrary to the phrase, they are not infrequent -- they occur every 2.7 years.
The last time two blue moons appeared within three months was in 1999.
"The term 'blue moon' actually has nothing to do with the color of the moon," Accuweather astronomy blogger Dave Samuhel said. "Blue moons are usually the same gray and white color of a regular [full] moon."
The moon cycles from one full moon to the next at an average of 29.53 days and is called a "synodic" month. Because February is the only calendar month that is shorter than a synodic month, it did not have a full moon this year -- so March ended up with an extra full moon.
The fourth full moon of the year is also known as worm full moon because it comes when earthworms emerge from their winter slumber, according to the Old Farmer's Almanac.
The January blue moon was considered "rare" because it also passed directly through Earth's shadow, producing a total lunar eclipse. The last time that occurred over North America was in 1866.
The March blue moon also will be a "Paschal" moon, the first full moon of spring, which began on March 20.
In addition, the first Sunday after the Paschal moon is usually designated as Easter Sunday. The last time a blue Paschal moon fell on March 31 and Easter Sunday on April 1 was in 1714.
Passover also starts on Friday night. The Jewish holiday starts at sundown on the 14th day of the Hebrew month Nisan -- falling in late March or early April on the Gregorian calendar -- and generally coincides with a full moon.