The weekend forecast is more complex than usual, thanks to something called a dirty ridge moving in, says KPLU weather expert Cliff Mass.
Sunny Friday Before Dirty Ridge Moves In
Friday will be a "very, very nice day" with sun and temperatures reaching the lower 70s, thanks to a ridge of high pressure in the skies above.
“A perfect fall day – well above normal," Mass said.
But he says on Saturday, something called a dirty ridge is expected to move in, bringing dueling weather regimes with it. A dirty ridge is an area of high pressure that’s not strong enough to push out all the clouds and rain. As a result, it will allow two weather regimes to settle in over the region.