The phrase "bipolar weather" refers to a situation where the weather constantly changes, ranging from warm or hot to cold, and back again. Full definition
You may think I'm talking crazy since it's May now, but if you're in Colorado, you'd understand how bipolar the weather could be. (withlovelilyrose.com)
And spring's bipolar weather drives me nuts... We had a pretty good winter, but then it snowed on the second day of spring, and it's currently sprinkling us with a light dusting of it now too. (runningwithattitude.com)