The Shamrock Shake shows up at McDonalds every year in late February and gets all revved up for St Patrick's Day. It's a true harbinger (that's haaaaah-bing-aaah!) of spring!
It's been around for years and years as evidenced by this old McDonalds commercial.
Even though it's not widely available yet, our sources say you can get one as of now at the Boston Post Rd location in Springfield and at the Shrewsbury St location in Worcester.