It will be the first spring equinox supermoon in 19 years, and won't happen again until 2030.
My heavens, what a splendid occurrence of celestial events we will be treated to this week. Not only do we finally get to usher in spring by means of the vernal equinox on March 20, but we get to do it by the light of a bonus supermoon.
The March 20 - 21st full moon will be the first full moon of spring in the Northern Hemisphere (and the first full moon of autumn for the Southern Hemisphere). The moon will also be at an exceptionally close distance in its orbit to Earth, meaning that it will appear 14 percent larger and 12 percent brighter than usual – thus, a supermoon.The equinox will occur on Wednesday, March 20 at 5:58 p.m. Eastern Time; the supermoon will be hot on its heels, officially reaching its full phase around four hours at 9:43 p.m.
A full moon and the spring equinox haven't occurred this closely since 2000, and won't sync up again until March of 2030. If there were ever a time to frolic in the woods, I'd say this is it.
Read more about the equinox here: 7 quirky facts about the vernal equinox.